Sligo Harbour - Department of Housing, Planning, Community and

Transcription

The Proposed Dredging of the Navigation
Channel at Sligo Harbour
Vol. 1: Environmental Appraisal Report
rpsgroup.com
Sligo Harbour Dredging
Environmental Appraisal Report
Contents
CONTENTS
VOLUME 1 – ENVIRONMENTAL APPRAISAL REPORT
1.0
INTRODUCTION .................................................................................................... 1-1
1.1
PROJECT SUMMARY ................................................................................ 1-1
1.2
EXISTING PORT FACILITIES ..................................................................... 1-2
1.3
STRATEGIC POLICY DRIVERS ................................................................. 1-4
1.3.1 National Policy ..................................................................................1-4
1.3.2 Regional/Local Policy........................................................................1-9
1.3.3 Other Relevant Policies ..................................................................1-15
1.4
PROJECT JUSTIFICATION ...................................................................... 1-17
1.4.1 Background ....................................................................................1-17
1.4.2 Sligo Port ........................................................................................1-19
1.4.3 Customers ......................................................................................1-22
1.4.4 Economic Impact ............................................................................1-24
1.4.5 The Economic Impact arising from Construction .............................1-27
1.4.6 The Positive Impact of Development...............................................1-28
1.4.7 Conclusion ......................................................................................1-29
1.5
CONSIDERATION OF ALTERNATIVES ................................................... 1-31
1.5.1 Alternative Locations.......................................................................1-31
1.5.2 Alternative Designs .........................................................................1-32
1.5.3 Alternative Processes .....................................................................1-34
1.6
THE CONSENTING PROCESS ................................................................ 1-44
1.6.1 Required Permissions .....................................................................1-44
2.0
3.0
CONSULTATIONS .................................................................................................. 2-1
2.1
STATUTORY CONSULTATIONS ............................................................... 2-1
2.2
DUMPING AT SEA CONSULTATIONS....................................................... 2-2
2.3
PUBLIC CONSULTATION .......................................................................... 2-5
2.4
ADDITIONAL OFFSHORE FISHERIES CONSULTATION .......................... 2-7
2.5
LOCAL AQUACULTURE............................................................................. 2-8
2.6
RESPONSE TO ISSUES RAISED DURING CONSULTATION ................... 2-8
2.7
CONCLUSIONS .......................................................................................... 2-8
SITE DESCRIPTION ............................................................................................... 3-1
3.1
INTRODUCTION ......................................................................................... 3-1
IBE00440/EAR/September ‘12
1
3.2
Contents
SITE CONTEXT AND EXISTING LAND USE.............................................. 3-3
3.2.1 Sligo Harbour Development ..............................................................3-3
3.3
NATURE CONSERVATION DESIGNATIONS ............................................ 3-4
3.3.1 Natura 2000 ......................................................................................3-4
3.3.2 Other Designations ...........................................................................3-9
4.0
PROJECT DESCRIPTION....................................................................................... 4-1
4.1
EXISTING CONDITIONS ............................................................................ 4-1
4.2
WATER INJECTION MAINTENANCE DREDGING AT JETTIES TO
-2.0M CD ..................................................................................................... 4-2
4.3
DESIGN OF PROPOSED CAPITAL & MAINTENANCE DREDGING WORKS
TO -3.0MCD ................................................................................................ 4-2
4.3.1 Channel Depth ................................................................................. 4-2
4.3.2 Channel Width ................................................................................. 4-5
4.3.3 Channel Side Slopes ....................................................................... 4-5
4.3.4 Channel Alignment .......................................................................... 4-5
4.3.5 Dredging Quantities ......................................................................... 4-5
4.4
PROPOSED DISPOSAL METHOD ............................................................. 4-6
4.5
DREDGING METHODOLOGY .................................................................... 4-6
4.5.1 Equipment ....................................................................................... 4-6
4.5.2 Dredging Programme....................................................................... 4-7
4.5.3 Personnel ........................................................................................ 4-8
4.5.4 Navigation........................................................................................ 4-8
4.5.5 Waste .............................................................................................. 4-8
5.0
BIRDS .................................................................................................................... 5-1
5.1
BACKGROUND........................................................................................... 5-1
5.1.1 Description of Proposed Works.........................................................5-1
5.1.2 Previous Information .........................................................................5-1
5.2
ASSESSMENT METHODOLOGY ............................................................... 5-2
5.2.1 Legislation and guidance ..................................................................5-2
5.2.2 Consultations ....................................................................................5-2
5.2.3 Desktop review .................................................................................5-3
5.3
FIELD SURVEYS ........................................................................................ 5-3
5.4
ECOLOGICAL EVALUATION AND IMPACT SIGNIFICANCE ..................... 5-4
5.5
BASELINE ENVIRONMENT........................................................................ 5-5
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Contents
5.5.1 Designated Areas for Nature Conservation .......................................5-5
5.5.2 Cummeen Strand SPA (Site Code 004035). .....................................5-6
5.5.3 Cummeen Strand/Drumcliff Bay candidate SAC (site code 0627) .....5-7
5.6
DESCRIPTION OF EXISTING BIRD POPULATIONS AND USAGE OF THE
AREA .......................................................................................................... 5-8
5.6.1 General description of the study area ...............................................5-8
5.6.2 Bird populations of the entire area of Sligo Harbour ..........................5-8
5.6.3 Bird usage of the area within 1km of the shipping channel..............5-10
5.6.4 Bird usage of the shipping channel and immediate banks only .......5-11
5.7
PREDICTED IMPACTS OF THE PROPOSED DREDGING ...................... 5-14
5.7.1 Potential impacts on birds ...............................................................5-14
5.7.2 Likely direct impacts on birds ..........................................................5-14
5.7.3 Impacts on the Tidal Regime of Sligo Harbour ................................5-16
5.8
LIKELY INDIRECT IMPACTS ON BIRDS.................................................. 5-17
5.9
MITIGATION MEASURES ........................................................................ 5-22
5.9.1 Mitigation by Reduction/Remedy ....................................................5-22
5.10
6.0
RESIDUAL IMPACTS ............................................................................... 5-22
INTERTIDAL AND SUBTIDAL FLORA AND FAUNA, MARINE MAMMALS ......... 6-1
6.1
INTRODUCTION ......................................................................................... 6-3
6.2
INTERTIDAL AND SUBTIDAL FLORA & FAUNA – DREDGING AREA ...... 6-4
6.2.1 Introduction ...................................................................................... 6-4
6.2.2 Desktop Study ................................................................................. 6-4
6.2.3 Field Survey – Aquafact 2010 ........................................................ 6-13
6.2.4 Sligo Harbour Intertidal and Subtidal Flora and Fauna - Predicted
Impacts ......................................................................................... 6-40
6.3
SUBTIDAL FLORA AND FAUNA – OFFSHORE DUMP SITE ................... 6-51
6.3.1 Introduction .................................................................................... 6-51
6.3.2 Results .......................................................................................... 6-58
6.3.3 Proposed Dumpsite Baseline Conditions - Conclusions ................. 6-69
6.3.4 Predicted Impacts at the Proposed Offshore Dump Site ................ 6-71
6.3.5 Mitigation of the Potential Impacts at the Dump Site and Residual
Impacts ......................................................................................... 6-74
6.4
MARINE MAMMALS ................................................................................. 6-75
6.4.1 Legislation pertaining to Marine Mammals in Irish waters .............. 6-75
6.4.2 Desktop Study of Marine Mammals in the Area ............................. 6-75
6.4.3 Site visit ......................................................................................... 6-80
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Contents
6.4.4 Potential Impacts of Dredging on Marine Mammals and Identification of
Sensitive Receptors. ..................................................................... 6-82
6.4.5 Direct, Indirect and Cumulative Impacts of Proposed Dredging and
Dumping of Dredged Material on Pinnipeds. ................................. 6-84
6.4.6 Direct, Indirect and Cumulative Impacts of Proposed Dredging and
Dumping of Dredged material on Cetaceans ................................. 6-86
6.4.7 Assessment of impact magnitude and significance ........................ 6-86
6.4.8 Marine Mammals - Mitigation Measures......................................... 6-87
6.4.9 Marine Mammals - Residual Impacts ............................................. 6-87
7.0
FISHERIES AND AQUACULTURE ......................................................................... 7-3
7.1
INTRODUCTION ......................................................................................... 7-3
7.2
COMMERCIAL FISHERIES ........................................................................ 7-3
7.2.1 Irish Brown Crab Fishery ................................................................. 7-3
7.2.2 The North West Crab Fishery .......................................................... 7-5
7.2.3 Other Inshore Fisheries ................................................................... 7-9
7.3
AQUACULTURE ....................................................................................... 7-12
7.3.1 Introduction .................................................................................... 7-12
7.3.2 Shellfish Production ....................................................................... 7-13
7.3.3 Annual Production ......................................................................... 7-15
7.4
Shellfish Waters Directive.......................................................................... 7-15
7.4.1 Classification of Shellfish Production Waters ................................. 7-16
7.5
SALMONID MIGRATIONS ........................................................................ 7-17
7.5.1 Life Cycle ....................................................................................... 7-17
7.5.2 Salmon Conservation..................................................................... 7-17
7.5.3 Local salmon/sea trout rivers ......................................................... 7-18
7.5.4 RECREATIONAL SEA ANGLING .................................................. 7-19
7.5.5 Shore Angling ................................................................................ 7-19
7.5.6 Boat Angling .................................................................................. 7-20
7.6
EEL & LAMPREY MIGRATIONS ............................................................... 7-20
7.6.1 Eel (Anguilla anguilla) .................................................................... 7-20
7.6.2 Lamprey......................................................................................... 7-20
7.7
IMPACT ASSESSMENT ........................................................................... 7-22
7.7.1 Potential Effects of Dredging and Disposal of Dredged Materials at
Sea ............................................................................................... 7-22
7.7.2 Socio-Economic and Conservation Aspects................................... 7-22
4
Contents
7.7.3 Impact Hypotheses ........................................................................ 7-24
7.7.4 Potential Impacts of the Scheme ................................................... 7-25
7.8
MITIGATION MEASURES ........................................................................ 7-28
7.8.1 Dredging Area................................................................................ 7-28
7.8.2 Dredge Disposal Site ..................................................................... 7-28
8.0
AIR AND CLIMATE ................................................................................................. 8-1
8.1
8.2
9.0
CLIMATE .................................................................................................... 8-1
8.1.1
Wind .................................................................................................8-1
8.1.2
Temperature .....................................................................................8-2
8.1.3
Precipitation ......................................................................................8-2
8.1.4
Potential Impacts on Climate ............................................................8-4
8.1.5
Potential Impacts on Air Quality ........................................................8-4
NOISE ......................................................................................................... 8-4
8.2.1
Existing Environment ........................................................................8-4
8.2.2
Evaluation Criteria ............................................................................8-4
8.2.3
Assessment of Temporary Construction Noise Impact ......................8-5
8.2.4
Comment on Noise Associated with Dredging ..................................8-6
8.2.5
Mitigating Measures for Temporary Construction Works ...................8-8
8.2.6
Conclusions ......................................................................................8-8
MATERIAL ASSETS ............................................................................................... 9-1
9.1
INFRASTRUCTURE ................................................................................... 9-1
9.1.1 Water Supply ....................................................................................9-1
9.1.2 Sewerage Infrastructure....................................................................9-2
9.1.3 Surface Water...................................................................................9-3
9.1.4 Mechanical and Electrical Services ...................................................9-5
9.2
TRAFFIC ..................................................................................................... 9-6
9.2.1 Background ......................................................................................9-6
9.2.2 Existing Baseline Conditions .............................................................9-6
9.2.3 Existing Flows taken from Model ......................................................9-8
9.2.4 Predicted Impacts During Dredging ..................................................9-9
9.2.5 Mitigation Measures..........................................................................9-9
9.2.6 Conclusions ....................................................................................9-10
9.2.7 Percentage Increase .......................................................................9-11
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Contents
10.0 GEOLOGY AND SOILS ........................................................................................ 10-1
10.1
SOLID GEOLOGY..................................................................................... 10-1
10.1.1 Regional Geology ...........................................................................10-2
10.2
HYDROGEOLOGY ................................................................................... 10-3
10.2.1 Potential Impacts to Groundwater ...................................................10-4
10.2.2 Predicted Impacts to Groundwater. .................................................10-5
10.3
GROUND CONDITIONS ........................................................................... 10-5
10.3.1 Dredging Area Sediment Physical Properties .................................10-5
10.4
OFFSHORE DISPOSAL SITE ................................................................... 10-8
10.4.1 INFOMAR Survey ...........................................................................10-8
10.4.2 Field Surveys ................................................................................10-11
10.4.3 Dumpsite Sediments Properties Conclusions ...............................10-14
11.0 HYDRODYNAMIC MODELLING ........................................................................... 11-1
11.1
COMPUTATIONAL MODEL OF WATER INJECTION DREDGING
OPERATIONS (5,500M³) .......................................................................... 11-1
11.1.1 Modelling Software ........................................................................ 11-1
11.1.2 Hydrodynamic Flow Model............................................................. 11-1
11.1.3 Bathymetry .................................................................................... 11-2
11.1.4 Model Calibration ........................................................................... 11-3
11.1.5 Model Simulations ......................................................................... 11-3
11.1.6 Dredging Plume Simulation Modelling ........................................... 11-5
11.1.7 Results of the Dredging Simulations .............................................. 11-9
11.1.8 Suspended Sediments, pH and Dissolved Oxygen ...................... 11-13
11.1.9 Sensitive Areas ............................................................................ 11-16
11.1.10Conclusion .................................................................................. 11-20
11.2
COMPUTATIONAL MODEL OF CONVENTIONAL DREDGING
OPERATIONS (250,000M³) .................................................................... 11-22
11.2.1 Introduction .................................................................................. 11-22
11.2.2 Computational Models ................................................................. 11-22
11.2.3 Model simulations ........................................................................ 11-23
11.2.4 Impacts of Dredging on Sensitive Habitats................................... 11-34
11.3
DUMPSITE PLUME MODELLING ........................................................... 11-43
11.3.1 Disposal Site Dispersion .............................................................. 11-43
11.3.2 Modelling System ........................................................................ 11-44
11.3.3 Ambient Tidal and flow Conditions ............................................... 11-46
11.3.4 Modelling Results ........................................................................ 11-48
6
Contents
11.3.5 Wave induced Sediment Transport .............................................. 11-56
11.3.6 Dumping at Sea Impacts Summary & Conclusions ...................... 11-57
12.0 CULTURAL HERITAGE ........................................................................................ 12-1
12.1
INTRODUCTION ....................................................................................... 12-1
12.2
ASSESSMENT METHODOLOGY ............................................................. 12-1
12.2.1 Limitations ......................................................................................12-2
12.2.2 Classification of Impacts/Effects .....................................................12-2
12.3
THE RECEIVING ENVIRONMENT ........................................................... 12-3
12.3.1 Overview.........................................................................................12-3
12.3.2 Placenames ....................................................................................12-5
12.3.3 Topographic files, National Museum of Ireland ...............................12-6
12.3.4 Record of Monuments and Places ..................................................12-6
12.3.5 Intertidal Survey ..............................................................................12-8
12.3.6 National Inventory of Architectural Heritage ....................................12-8
12.3.7 Cartographic Sources .....................................................................12-9
12.3.8 Shipwreck Inventory .......................................................................12-9
12.3.9 Licensed archaeological work .......................................................12-11
12.3.10 Conclusion...................................................................................12-11
12.4
ARCHITECTURAL SITE ASSESSMENT ................................................ 12-12
12.5
MARINE GEOPHYSICAL SURVEY ........................................................ 12-12
12.5.1 Nature of record ............................................................................12-13
12.5.2 Harbour ........................................................................................12-13
12.5.3 Marine Disposal Area....................................................................12-15
12.5.4 Conclusion ....................................................................................12-16
12.6
PREDICTED IMPACTS ........................................................................... 12-17
12.7
RECOMMENDATIONS ........................................................................... 12-17
12.7.1 Pre-construction Measures ...........................................................12-17
12.7.2 Construction Phase Measures ......................................................12-17
12.7.3 Archaeological/Cultural Heritage Management .............................12-17
12.8
13.0
FIGURES ................................................................................................ 12-19
HUMAN BEINGS................................................................................................... 13-1
13.1
INTRODUCTION ....................................................................................... 13-1
13.2
SOCIO-ECONOMIC PROFILE .................................................................. 13-1
13.3
ECONOMIC PROFILE .............................................................................. 13-2
7
Contents
13.3.1 Labour Force ..................................................................................13-2
13.3.2 Fisheries and Aquaculture ..............................................................13-4
13.3.3 Sligo Port ........................................................................................13-4
13.4
TOURISM.................................................................................................. 13-5
13.4.1 Bathing Waters ...............................................................................13-8
13.4.2 Sailing.............................................................................................13-8
13.5
CONCLUSIONS ........................................................................................ 13-9
13.5.1 Predicted Impacts ...........................................................................13-9
13.5.2 Mitigation Measures........................................................................13-9
13.5.3 Residual Impacts ............................................................................13-9
8
14.0
Contents
WATER QUALITY AND SEDIMENT .................................................................... 14-1
14.1
OVERVIEW OF EXISTING LEGISLATION ............................................... 14-1
14.1.1 Bathing Waters ...............................................................................14-1
14.1.2 Shellfish Waters ..............................................................................14-2
14.1.3 The Water Framework Directive .....................................................14-3
14.2
EXISTING WATER QUALITY.................................................................... 14-5
14.2.1 Bathing Waters ...............................................................................14-5
14.2.2 Shellfish waters...............................................................................14-6
14.2.3 The Water Framework Directive .....................................................14-7
14.3
SEDIMENT QUALITY ............................................................................. 14-10
14.3.1 Dredging Area – Sediment Chemical Properties ...........................14-10
14.3.2 Dredged Sediments Properties Conclusions .................................14-14
14.4
POTENTIAL IMPACTS DURING DREDGING ......................................... 14-14
14.4.1 Short term increase in Suspended Sediment and Turbidity...........14-14
14.4.2 Potential for the Spread of Contaminated Dredged Material .........14-16
14.4.3 Potential for impacts to Dissolved Oxygen and Nutrients ..............14-16
14.4.4 Potential for impact on Water Quality in the wider Sligo Bay Area.14-16
14.4.5 Accidental Spillages during Dredging Operations .........................14-17
15.0
SUMMARY OF IMPACTS AND MITIGATION MEASURES ................................. 15-1
15.1
INTRODUCTION ....................................................................................... 15-1
15.2
TECHNICAL DIFFICULTIES ..................................................................... 15-1
15.3
INTERACTIONS AND CONCLUSIONS .................................................. 15-18
9
Contents
LIST OF FIGURES
CHAPTER 1 - INTRODUCTION
Figure 1.1: Border Region Relationships in terms of the NSS............................................ 1-7
Figure 1.2: Irish Port Traffic ............................................................................................. 1-19
Figure 1.3: Sligo Port Traffic ............................................................................................. 1-21
Figure 1.4:Former Finisklin Landfill .................................................................................. 1-38
Figure 1.5: Suggested Reclamation Area ......................................................................... 1-40
CHAPTER 2 – CONSULTATIONS
Figure 2.1 Dumpsite Consulted Sites ............................................................................. 2-3
Figure 2.2 Pot Fishing area as indicated in Public Consultations.................................... 2-7
CHAPTER 3 – SITE DESCRIPTION
Figure 3.1
Figure 3.2
Figure 3.3 Figure 3.4
Figure 3.5
Site Location (Regional Context) ................................................................... 3-1
SAC Designated Areas ................................................................................. 3-7
SPA Designated Areas.................................................................................. 3-9
pNHA and Ramsar Designated areas ......................................................... 3-10
EU Shellfish Waters .................................................................................... 3-11
CHAPTER 4 – PROJECT DESCRIPTION
Figure 4.1 : Dredging Area ................................................................................................ 4-3
Figure 4.2 : Dumpsite ........................................................................................................ 4-4
Figure 4.3: Example of a Trailing Suction Dredger ............................................................ 4-6
Figure 4.4:Example of a Backhoe Dredger ....................................................................... 4-7
CHAPTER 5 - BIRDS
Figure 5.1: Area of the shipping channel surveyed as part of the bird surveys over the period
December 2009 – November 2010 ..................................................................................... 5-4
Figure 5.2: Cummeen Strand SPA boundary (updated February 2012) ............................. 5-5
CHAPTER 6 – INTERTIDAL AND SUBTIDAL FLORA & FAUNA, MARINE
MAMMALS
Figure 6.1: Map showing the location of the 30 intertidal stations surveyed by ASU in 2007
. .......................................................................................................................................... 6-8
Figure 6.2: Figure showing location of transects surveyed by ASU in Sligo Bay, 2007. ...... 6-9
Figure 6.3: Location map for the sites surveyed by BIOMAR and OPW teams in Sligo Bay
1996 ............................................................................................................... 6-12
Figure 6.4: Map showing recent intertidal survey effort, Sligo Harbour. ............................ 6-15
Figure 6.5: Location of observations made during the walkover survey, October 2010. .... 6-15
Figure 6.6: Trestles, clam farm site, Sligo Harbour, 07th October 2010. ............................ 6-16
Figure 6.7: Commercial clam park. South west Sligo Harbour, 07th October 2010. ........... 6-17
Figure 6.8: Mussel bed, Sligo beach, 07th October 2010................................................... 6-17
Figure 6.9: Mussel bed, close view. A mix of blue mussel and clams. .............................. 6-18
10
Contents
Figure 6.10: Algae (primarily fucoids) on mussel bank, Sligo Harbour, October 2010. ...... 6-18
Figure 6.11: Lugworm feeding casts, near mussel bank, Sligo harbour, October 2010. .... 6-19
Figure 6.12: Seagrass and lugworm feeding casts, Sligo Harbour, October 2010. ........... 6-19
Figure 6.13: Vaucheria sp. mat over intertidal muddy fine sand flat, Sligo Harbour, 07th
October 2010. ..............................................................................................6-20
Figure 6.14: Gooses feeding on the intertidal sand flat, 07th October 2010. ...................... 6-21
Figure 6.15: Fyke net on pole, Sligo Harbour, 07th October 2010 ..................................... 6-21
Figure 6.16: Mussel bank, Sligo Harbour, 07th October 2010............................................ 6-22
Figure 6.17: Mussel bank Sligo Harbour, 07th October 2010............................................. 6-22
Figure 6.18: Commercial clam park (Noel Carter’s). ......................................................... 6-23
Figure 6.19: Clam cultivation hardware, Sligo Harbour, 07th October 2010. ...................... 6-23
Figure 6.20: Rippled fine sand surrounding clam cultivation site, 07 th October 2010......... 6-24
Figure 6.21: Intertidal area with filamentous algal growth, Sligo Harbour, October 2010 .. 6-24
Figure 6.22: Points of interest near the navigation channel walkover area 7 th October
2010............................................................................................................. 6-25
Figure 6.23: Rippled fine sand with some algae, 08th October 2010. ................................ 6-26
Figure 6.24: Channel marker, Sligo harbour, 08th October 2010. ...................................... 6-26
Figure 6.25: Base of channel marker & training wall, Sligo harbour, 08 th October 2010. ... 6-27
Figure 6.26: Intertidal sand flat, Sligo Harbour, 08th October 2010.................................... 6-27
Figure 6.27: View towards Sligo along navigation channel, 08th October 2010. ................ 6-28
Figure 6.28: Encrusting flora and fauna on the northern Sligo harbour navigation channel
training wall, Sligo Harbour, 08th October 2010................................................................. 6-29
Figure 6.29: Muddy sand flat adjacent to training wall, Sligo harbour approach channel, 08th
October 2010. ..............................................................................................6-29
Figure 6.30: Map showing subtidal sampling locations ..................................................... 6-31
Figure 6.31: Dendrogram showing the natural grouping of each station sampled in Sligo
Harbour.......................................................................................................6-37
Figure 6.32: MDS ordination showing the natural grouping of each station sampled in Sligo
Harbour........................................................................................................6-37
Figure 6.33: Sediment grain size data .............................................................................. 6-40
Figure 6.34: Sediment type according to Folk (1954)........................................................ 6-40
Figure 6.35: Location of Proposed Offshore 1km² Dump Site .......................................... 6-52
Figure 6.36: Sampled stations at proposed dump site, Donegal Bay, Jan/Feb 2011........ 6-54
Figure 6.37: Locations of Faunal Stations, Donegal Bay, Jan/Feb 2011 .......................... 6-56
Figure 6.38: Video transect locations in the vicinity of the proposed dumpsite, Donegal Bay,
January 2011. ..............................................................................................6-59
Figure 6.39 Current and tide measurements, Donegal Bay, Jan & Feb 2011................... 6-60
Figure 6.40 Ebb drogue tracks, Donegal Bay, 27.1.2011 ................................................. 6-61
Figure 6.41: Flood drogue tracks, Donegal Bay, 27.1.2011 .............................................. 6-62
Figure 6.42 Flood drogue tracks, Donegal Bay, 17.2.2011 ............................................... 6-63
Figure 6.43 Ebb drogue tracks, Donegal Bay, 17.2.2011 ................................................. 6-63
Figure 6.44 Dendrogram showing the natural grouping of each station sampled in Donegal
Bay. ............................................................................................................ 6-66
Figure 6.45: MDS plot of all stations sampled in Donegal Bay. ........................................ 6-67
Figure 6.47: Survey Area ................................................................................................. 6-82
Figure 6.48: Vantage point for marine mammal survey on south shore of Sligo Harbour . 6-83
11
Contents
Figure 6.49: North shore of Sligo Harbour at low tide, scanned for hauled-out pinnipeds.6-83
Figure 6.50: Proposed dredging area showing main environmental designations ............ 6-86
CHAPTER 7 – FISHERIES AND AQUACULTURE
Figure 7.1: National landings of brown crab between 1952 and 2004 (from Tully et al, 2006;
reproduced by permission of BIM) ...................................................................................... 7-3
Figure 7.2:Probable distribution of the northwest crab stock (from Tully et al, 2006;
reproduced by permission of BIM) ...................................................................................... 7-5
Figure 7.3: Annual landings of crab into Donegal and Mayo, 1990-2004 (from Tully et al,
2006; reproduced by permission of BIM) ............................................................................ 7-5
Figure 7.4: Landings of crab by statistical rectangle by the Mayo and Donegal <12m fleets in
2004 (from Tully et al, 2006; reproduced by permission of BIM) ......................................... 7-6
Figure 7.5: Size composition of male and female crab in the inshore landings 1996/97 (from
Tully et al, 2006; reproduced by permission of BIM) ........................................................... 7-7
Figure 7.6:Distribution of fishing in the <12m and vivier crab fisheries in 1997 (from Tully et
al, 2006; reproduced by permission of BIM) ....................................................................... 7-9
Figure 7.7: Distribution of fishing in the <12m and vivier crab fisheries in 2004-2005 (from
Tully et al, 2006; reproduced by permission of BIM) ......................................................... 7-10
Figure 7.8: Sites licensed for shellfish production in the Sligo area.................................. 7-12
Figure 7.9: Map of region showing principal salmonid rivers draining to Sligo Bay........... 7-17
Figure 7.10: Annual salmon catch from principal local rivers, 2001-10 (Source: IFI) ........ 7-18
Figure 7.11: The potential environmental impacts of marine dredging - a conceptual model 722
Figure 7.12: The potential environmental impacts of marine dredged material disposal - a
conceptual model ............................................................................................................. 7-22
CHAPTER 8 – AIR AND CLIMATE
Figure 8.1: Windrose for Belmullet Meteorological station 1957-2010 ............................... 8-1
Figure 8.2: 30 year monthly average temperatures (Belmullet) and sea temperatures (Malin)
........................................................................................................................................... 8-2
Figure 8.3: Met Éireann 1961-1990 mean annual average rainfall ..................................... 8-3
Figure 8.4: Met Éireann Average Monthly Rainfall for 5km² containing Sligo Harbour ....... 8-3
Figure 8.5: Location of Dredging Area ............................................................................... 8-5
CHAPTER 9 - MATERIAL ASSETS
Figure 9.1: Sligo WWTP at Finisklin .................................................................................. 9-2
Figure 9.2: Junctions in Vicinity of Port .............................................................................. 9-7
CHAPTER 10 – GEOLOGY AND HYDROGEOLOGY
Figure 10.1:
Figure 10.2:
Figure 10.3:
Figure 10.4:
Figure 10.5:
Figure 10.6:
Figure 10.7
Site Location ................................................................................................ 10-1
Local Geology, from GSI 100k mapping ...................................................... 10-2
Bedrock Aquifers ......................................................................................... 10-3
Groundwater Status (2010).......................................................................... 10-4
Vibrocore sample stations............................................................................ 10-5
Vibrocorer .................................................................................................... 10-7
GSI/Marine Institute INFOMAR Moraine Shaded Relief Image ................ 10-9
12
Figure 10.8 Figure 10.9 Contents
GSI Backscatter Image of Dumpsite ...................................................... 10-10
Grab Sample Stations January/February 2011 ...................................... 10-11
CHAPTER 11 - COASTAL PROCESSES - HYDRODYNAMIC MODELLING
Figure 11.1: Extent of 30 and 10 metre grid nested flow model ....................................... 11-2
Figure 11.2: Extent of LiDAR Bathymetry and 2011 Bathymetric Survey .......................... 11-3
Figure 11.3: Tidal curve for 1 month simulation period. .................................................... 11-4
Figure 11.4: Typical flow patterns in Sligo harbour - flood tide .......................................... 11-4
Figure 11.5: Typical flow patterns in Sligo harbour - ebb tide........................................... 11-5
Figure 11.6: Target areas (A-E) for maintenance dredging by Water Injection Dredging . 11-7
Figure 11.7: Peak sediment deposition depths in Sligo Harbour during water injection
dredging operations........................................................................................................ 11-11
Figure 11.8: Final sediment deposition depths on completion of water injection dredging
operations ...................................................................................................................... 11-12
Figure 11.9: Mean suspended sediment concentrations during water injection dredging
operations (for bottom 0.5m of water column)................................................................. 11-15
Figure 11.10: Location of Identified Sensitive Areas and Timeseries Locations ............. 11-16
Figure 11.11: Time series showing peak Suspended Sediment Concentration in bottom 0.5m
and Sedimentation for Carton Marsh Area during dredging campaign (Point Mon-1)...... 11-17
Figure 11.12: Time series showing peak Suspended Sediment Concentration in bottom
0.5m and Sedimentation for Southern part of Cummeen Strand during dredging campaign
(Point Mon-2) ................................................................................................................. 11-18
0.5m and Sedimentation near commercial shellfish farm during dredging campaign (Point
Mon-3) ............................................................................................................................ 11-19
Figure 11.14: Time Series showing peak Suspended Sediment Concentration in bottom
0.5m and Sedimentation for commercial clam farm during dredging campaign (Point Mon-4)
....................................................................................................................................... 11-20
Figure 11.15: Extent of 30 and 10 metre grid nested flow model ................................... 11-22
Figure 11.16 ................................................................................................................... 11-23
Figure 11.16: Comparison of existing and dredged channel tidal curves at Sligo (neap tide)
....................................................................................................................................... 11-24
Figure 11.17: Comparison of existing and dredged channel tidal curves at Sligo (overall
average) ......................................................................................................................... 11-25
Figure 11.18: Comparison of existing and dredged channel tidal curves at Sligo (extreme
spring tide) ..................................................................................................................... 11-25
Figure 11.19 ................................................................................................................... 11-26
Figure 11.19: Difference in mean spring flood tide velocity - proposed minus existing ... 11-26
Figure 11.20: Difference in mean spring ebb tide velocity - proposed minus existing..... 11-27
Figure 11.21 ................................................................................................................... 11-27
Figure 11.21: Difference in peak spring flood tide velocity - proposed minus existing .... 11-27
Figure 11.22: Difference in peak spring ebb tide velocity - proposed minus existing ...... 11-28
Figure 11.23: Tidal curve for hydrodynamic regime used in the dredging simulations.... 11-29
Figure 11.24 ................................................................................................................... 11-31
Figure 11.24 Peak sediment deposition depths during dredging of lower channel ...... 11-32
Figure 11.25 Peak sediment deposition depths during dredging of upper channel...... 11-32
13
Contents
Figure 11.26 Sediment deposition depths on completion of all dredging operations ... 11-33
Figure 11.27: Location of potentially vulnerable areas ................................................... 11-34
Figure 11.28: Lower channel dredging - mean suspended sediment concentration in Area 1
– Cartron/Standalone Point ............................................................................................ 11-35
Figure 11.29: Lower channel mean suspended sediment concentration in Area 2 – seagrass
habitat in southern part of Cummeen Strand .................................................................. 11-35
Figure 11.30: Lower channel mean suspended sediment concentration in Area 3 –
commercial shellfish farm ............................................................................................... 11-36
Figure 11.31: Mean suspended sediment concentration in lower 0.5m of water column
during dredging of the upper section of the channel ....................................................... 11-36
Figure 11.32: Upper channel dredging - mean suspended sediment concentration in Area 1
–Cartron Marsh/Standalone Point................................................................................... 11-37
Figure 11.33: Upper channel dredging - mean suspended sediment concentration in Area 2
– Seagrass habitat in southern part of Cummeen Strand ............................................... 11-37
Figure 11.34: Upper channel mean suspended sediment concentration in Area 3 –
commercial and natural shellfish beds ............................................................................ 11-38
Figure 11.35: Mean suspended sediment concentration in bottom 0.5m at location of 4
points in potential vulnerable areas ................................................................................ 11-40
Figure 11.36: Time series showing Suspended Sediment Concentration in Cartron Marsh
Area during dredging (Point 1)........................................................................................ 11-40
Figure 11.37: Time series showing Suspended Sediment Concentration in Southern part of
Cummeen Strand during dredging (Point 2) ................................................................... 11-41
Figure 11.38: Time series showing Suspended Sediment Concentration near commercial
shellfish farm during dredging (Point 3) .......................................................................... 11-41
Figure 11.39: Time Series showing Suspended Sediment Concentration near commercial
clam farm during dredging (Point 4)................................................................................ 11-41
Figure 11.40: Extents of sediment dumping hydrodynamic model (blue square) and
proposed dump site location (red square)....................................................................... 11-43
Figure 11.41: Flexible mesh model base model............................................................. 11-45
Figure 11.42: Flexible mesh model – zoomed extents ................................................... 11-46
Figure 11.43: Extent of 45m grid with deposition area marked by yellow square ........... 11-46
Figure 11.44: Tidal elevations at the dump site over simulation period .......................... 11-47
Figure 11.45: Tidal flow around deposition site - Mid flood spring tide ........................... 11-47
Figure 11.46: Tidal flow around deposition site - Mid ebb spring tide ............................. 11-48
Figure 11.47: Measured and modelled current speed – site of drogue release 1 spring Tide
....................................................................................................................................... 11-49
Figure 11.48: Measured and modelled current direction – site of drogue release 2 spring tide
....................................................................................................................................... 11-49
Figure 11.49: Measured and modelled current speed – site of drogue release 1 neap tide 1150
Figure 11.50: Measured and modelled current speed – site of drogue release 2 neap tide 1150
Figure 11.51: Drogue track at neap tide in mid layer (drop at high water) and particle track
from the model ............................................................................................................... 11-51
Figure 11.52: Drogue track at Spring tide - mid layer (drop at low water) and particle track
from the model ............................................................................................................... 11-51
14
Contents
Figure 11.53: Drogue track at mid layer (mid flood drogue drop) and particle track from the
model ............................................................................................................................. 11-52
Figure 11.54: Drogue track at mid layer (mid ebb drogue drop) and particle track from the
model ............................................................................................................................. 11-52
Table 11.11.5: Grain diameter occurrence used in modelling ......................................... 11-53
Figure 11.55: Track of suspended sediment over a month of tides ................................ 11-54
Figure 11.56: Maximum suspended sediment concentration in the water column .......... 11-55
Figure 11.57: Mean suspended sediment concentration in the water column ................ 11-55
Figure 11.58: Final Deposition of sediment at the end of dredging operations ............... 11-56
Figure 11.59: Significant wave height Donegal Bay ....................................................... 11-57
Figure 11.60: Mean wave period Donegal Bay .............................................................. 11-57
CHAPTER 12 – CULTURAL AND ARCHITECTURAL HERITAGE
Figure 12.1: Admiralty Chart showing Harbour area and proposed dredging works ... 12-19
Figure 12.2: Admiralty Chart showing proposed marine disposal site. ........................... 12-19
Figure 12.3: Distribution of RMP sites in Harbour area. ................................................ 12-20
Figure 12.4: Distribution of NIAH sites in Harbour area. ................................................ 12-20
Figure 12.5: Extract from 1859 sea chart showing the location of the Fancy. ................ 12-21
Figure 12.6: Extracts from OS First Edition 1838 Sheet 14 and Third Edition ................ 12-22
Figure 12.7: Map of known wrecksites in the vicinity of the marine disposal site............ 12-23
Figure 12.8: The Hans Broge, before she wrecked, c. 1907. ......................................... 12-23
Figure 12.9: Marine geophysical survey tracklines within the Harbour area. .................. 12-24
Figure 12.10: Seabed images from the sonar data, Harbour area. ................................ 12-24
Figure 12.11: Sonar trace showing the terminal perch, ss5. .......................................... 12-25
Figure 12.12: Sonar trace showing anomaly ss25 within its local context. ...................... 12-26
Figure 12.13: Distribution of marine geophysical anomalies observed within the Harbour
area. ............................................................................................................................... 12-27
area, East side. .............................................................................................................. 12-27
area, central zone........................................................................................................... 12-28
area, West side. ............................................................................................................. 12-28
Figure 12.17: Marine geophysical survey tracklines at the marine disposal site............. 12-29
Figure 12.18: Sonar trace showing nature of seabed imaged at the marine disposal site. . 1230
Figure 12.19: Distribution of marine geophysical anomalies observed at the marine disposal
site. ................................................................................................................................ 12-31
CHAPTER 13 – HUMAN BEINGS
Figure 13.1 Population pyramids (2011 census) for State and Sligo County ............... 13-2
Figure 13.2 Composition of Working Labour Force in Co. Sligo and State (2006) ............ 13-3
Figure 13.4 North West Region Overseas Visitor Numbers 1999-2009 ...................... 13-6
CHAPTER 14 – SEDIMENT AND WATER QUALITY
15
Figure 14.1:
Figure 14.2:
Figure 14.3:
Figure 14.4:
Figure 14.5:
Contents
Designated Bathing Water ........................................................................... 14-1
Sligo Bay and Drumcliff Bay EC Designated Shellfish Waters ..................... 14-2
Water Framework Directive Water Body Boundaries and Overall Status ..... 14-4
Bathing Water Quality Status ....................................................................... 14-6
Sligo Sediment Chemical Sampling Stations ............................................. 14-11
CHAPTER 15 – SUMMARY OF IMPACTS AND MITIGATION MEASURES
(no figures)
16
Contents
LIST OF TABLES
CHAPTER 1 – INTRODUCTION
Table 1.1: Irish Port Traffic .............................................................................................. 1-21
Table 1.2: Sligo Port Traffic ............................................................................................. 1-22
Table 1.3: Sligo Port 2008 - 2011 Traffic Details.............................................................. 1-22
Table 1.4: Sligo Port 2010 and 2011 Traffic Details ......................................................... 1-23
Table 1.5: Employment associated with Harbour Activity................................................. 1-26
Table 1.6: Comparison of Navigable Period with Dredged Depth ..................................... 1-34
CHAPTER 2 – CONSULTATIONS
Table 2.1 Organisations/Agencies consulted as part of the Appraisal Process ................... 2-1
CHAPTER 3 – SITE DESCRIPTION
Table 3.1
Table 3.2 Cummeen Strand/Drumcliff Bay SAC Summary ............................................ 3-6
Sligo Harbour and Drumcliff Bay SPA Summary ........................................... 3-8
CHAPTER 4 – PROJECT DESCRIPTION
(no tables)
CHAPTER 5 – BIRDS
Table 5.1:Irish Wetlands Bird Survey (IWeBS) peak counts in Sligo Harbour (entire estuary).
........................................................................................................................................... 5-8
Table 5.2: Summary of peak and mean numbers of water birds within 1km of the shipping
channel in Sligo Harbour over ten months, December 2009-November 2010................... 5-11
Table 5.3: Summary of peak and mean numbers of water birds on the shipping channel and
its immediate banks in Sligo Harbour over ten months, December 2009-November 2010.5-12
Table 5.4: Tolerance thresholds of Zostera spp. to turbidity levels................................... 5-20
Table 5.5: Tolerance thresholds for Zostera spp. to sedimentation. ................................. 5-20
CHAPTER 6 – INTERTIDAL AND SUBTIDAL FLORA & FAUNA, MARINE
MAMMALS
Table 6.1: Subtidal station co-ordinates............................................................................ 6-31
Table 6.2: The classification of sediment particle size ranges into size classes ................ 6-32
Table 6.3: Diversity indices for the 15 stations sampled in Sligo Harbour. ........................ 6-35
Table 6.4: SIMPER Results .............................................................................................. 6-38
Table 6.5: Granulometry results for the 14 stations sampled in Sligo Harbour (as percentage
weight of the total sample)................................................................................................ 6-39
Table 6.6: Sediment organic carbon results for the fourteen stations surveyed off Sligo, 6th
October, 2010. ............................................................................................... 6-41
Table 6.7: Summary of critical thresholds for mussel (Mytilus edulis) beds....................... 6-49
Table 6.8: Tolerance thresholds of Zostera spp. to turbidity levels.................................... 6-50
Table 6.9: Tolerance thresholds for Zostera spp. to sedimentation. .................................. 6-50
Table 6.10: Locations of the sediment sampling stations in Donegal Bay. ....................... 6-54
Table 6.11 Diversity indices for the 4 stations sampled in Donegal Bay............................ 6-65
Table 6.12 Descriptions of the video transects, Donegal Bay, January 2011. .................. 6-68
17
Contents
Table 7.1: Total landings of brown crab into Irish ports, 2001-10 (Source: SFPA) .............. 7-3
Table 7.2: Clam and oyster production in the Sligo Bay area, 2006-11 (Source: BIM) ..... 7-14
Table 7.3: Classification of designated bivalve mollusc production areas, 2012 .............. 7-15
Table 7.4: Summary of migrations/presence of eel and lamprey in local estuaries at different
times of year..................................................................................................................... 7-20
CHAPTER 8 – AIR AND CLIMATE
Table 8.1: Example Threshold of significant impact at dwellings
8-6
CHAPTER 9 - MATERIAL ASSETS
Table 9.1: Docking Pattern at Sligo Harbour...................................................................... 9-6
Table 9.2: Existing Traffic Flows along Primary Route ....................................................... 9-8
Table 9.3: Percentage increase during dredging operations ............................................ 9-11
CHAPTER 10 – GEOLOGY AND HYDROGEOLOGY
Table 10.1: Summary of Sediment Conditions ................................................................. 10-7
Table 10.2 Results of the granulometric analysis on the dump site sediments ........ 10-12
Table 10.3 Physical properties of the dump site sediments ..................................... 10-12
Table 10.4 Proposed Dumpsite Baseline Sediment Testing Results............................... 10-13
CHAPTER 11 - COASTAL PROCESSES - HYDRODYNAMIC MODELLING
Table 11.1: Dredging Area Sediment Samples – Descriptions......................................... 11-7
Table 11.2: Dredging Area Sediment Samples – Granulometry Results ........................... 11-8
Table 11.3: Measured suspended sediment in Sligo Harbour ........................................ 11-13
Table 11.4: Water Quality Measurements in Sligo Harbour ........................................... 11-39
CHAPTER 12 – CULTURAL AND ARCHITECTURAL HERITAGE
Table 12.1 Townlands and placenames identified within the Sligo study area............... 12-5
Table 12.2 Side-scan sonar anomalies identified within the harbour area* ..................... 12-14
Table 12.3 Magnetometer anomalies identified within the harbour area* ................. 12-15
Table 12.4 Side-scan sonar anomalies identified on marine disposal area survey* . 12-16
CHAPTER 13 – HUMAN BEINGS
(no tables)
CHAPTER 14 – SEDIMENT AND WATER QUALITY
Table 14.1: Site Area Transitional and Coastal Waterbody Status ................................... 14-8
Table 14.2: Site Area River water body status ................................................................. 14-8
Table 14.3: Dredging Area Sediment Samples - Descriptions ....................................... 14-11
CHAPTER 15 – SUMMARY OF IMPACTS AND MITIGATION MEASURES
Table 15.1 Summary of Potential Impacts and Proposed Mitigation Measures................. 15-2
Table 15.2 Interactions ................................................................................................... 15-15
18
Contents
VOLUME 2 - LIST OF APPENDICES
APPENDIX 1 - INTRODUCTION
Appendix IA: Harbour Office Submission In Relation To The Docklands Local Area Plan
APPENDIX 2 – CONSULTATIONS
Appendix 2A: Summary of Consultee Responses
Appendix 2B: Public Consultation Display Information
Appendix 2C: Copy of Written Consultee Responses
APPENDIX 3 – BIRDS
Appendix 3A: Bird Field Survey Counts
Appendix 3B: Screening For Appropriate Assessment
APPENDIX 4 – INTERTIDAL AND SUBTIDAL FLORA & FAUNA,
MARINE MAMMALS
Appendix 4A: Biomar Survey Data – Sligo Bay
Appendix 4B: SAC Site Synopses
Appendix 4C: Benthic Fauna Species List
Appendix 4D: Ecological Site Evaluation Criteria
Appendix 4E: Dump Site Current Metering and Drogue Tracking Results
Appendix 4F: Dump Site Area Infaunal Sampling Species List
Appendix 4G: Dumpsite ROV Video 163
Appendix 4H: Dumpsite Benthos Simper Similarity Percentages
APPENDIX 5 – FISHERIES
APPENDIX 5 - ICES Areas and Atlas Of Commercial Fisheries
APPENDIX 6 – GEOLOGY AND HYDROGEOLOGY
APPENDIX 6A: Vibrocore Report
Appendix 6B: Dump Site Granulometric Testing Results
APPENDIX 7 – CULTURAL HERITAGE
APPENDIX 7A: Known Archaeological And Architectural Heritage Records for the Sligo
Harbour and Marine Disposal Areas
APPENDIX 7B: Observation Of Marine Geophysical Survey Anomalies.
APPENDIX 7C: Architectural Heritage Assessment
APPENDIX 7D: Marine Geophysical Survey
APPENDIX 8 - SEDIMENT AND WATER QUALITY
APPENDIX 8A: Report on Dredging Sediment Testing
APPENDIX 8B: Dumpsite Grab Sample Chemical Testing Results [Data DVD-ROM]
20
Contents
VOLUME 3 – NATURA IMPACT STATEMENT
1. INTRODUCTION ...................................................................................................... 1
1.1.
The requirement for an assessment under Article 6 ................................. 1
1.2.
The aim of this report ............................................................................... 2
1.3.
Background – an overview of the Sligo Harbour Dredging project ............ 2
1.4.
Consultation ............................................................................................. 3
1.4.1. Government Departments.................................................................... 3
1.4.2. Other Bodies........................................................................................ 3
1.5.
Constraints ............................................................................................... 4
2. THE APPROPRIATE ASSESSMENT PROCESS .................................................... 4
2.1.
Introduction .............................................................................................. 4
2.2.
Stages ...................................................................................................... 6
2.3.
Alternatives .............................................................................................. 7
2.3.1. Introduction .......................................................................................... 7
2.3.2. Alternative dredging methods .............................................................. 7
2.3.3. Alternative timing of works ................................................................... 8
2.3.4. Alternative dredge spoil disposal methods ........................................... 8
2.3.5. Alternative sea disposal sites ............................................................... 8
3. THE ECOLOGICAL IMPACT ASSESSMENT .......................................................... 9
3.1.
Introduction .............................................................................................. 9
3.1.1. Description of the project ................................................................... 10
4. NATURA 2000 SITES ............................................................................................ 11
4.1.
Areas and Species of Scientific Interest – Sligo Harbour ........................ 12
4.1.1. Areas of Scientific Interest (ASI) ........................................................ 13
4.1.2. Special Areas of Conservation (SAC) ................................................ 15
4.1.3. Special Protection Area (SPA) ........................................................... 16
4.1.4. Natural Heritage Area (NHA) ............................................................. 16
4.1.5. Designations under the Wildlife Act, 1976 .......................................... 17
4.1.6. Proposed Nature Reserve in private ownership ................................. 17
4.1.7. County Geological Sites..................................................................... 17
4.1.8. International Reserves/Conventions .................................................. 17
4.2.
Designated sites in the vicinity of the project .......................................... 18
4.2.1. Sligo Harbour..................................................................................... 19
4.3.
Characteristics of the designated sites ................................................... 20
4.3.1. Cummeen Strand/Drumcliff Bay SAC (Site code: 000627) ................. 20
4.3.2. Cummeen Strand SPA (Site code: 004035) ....................................... 24
22
Contents
4.3.3. Lough Gill SAC (Site code: 001976) .................................................. 27
4.4.
Desk Study ............................................................................................. 31
4.4.1. Intertidal habitats ............................................................................... 31
4.5.
Field Survey – AQUAFACT 2010 ........................................................... 52
4.5.1. Intertidal survey 2010......................................................................... 52
5. ASSESSMENT OF LIKELY EFFECTS .................................................................. 85
5.1.
Consideration of significance .................................................................. 85
5.2.
Potential impacts on Natura 2000 sites – impacts prediction .................. 87
5.2.1. Potential impacts on Cummeen Strand/Drumcliff Bay SAC ................ 87
5.2.2. Potential impacts on Cummeen Strand SPA ...................................... 93
5.2.3. Indirect Impacts on Natura sites in the wider locality, including Lough
Gill SAC ............................................................................................ 98
5.2.4. Cumulative Impacts ........................................................................... 98
6. MITIGATION MEASURES ................................................................................... 103
6.1.
Habitats in Cummeen Strand/Drumcliff Bay SAC ................................. 103
6.1.1. The removal of estuarine sediments ................................................ 103
6.1.2. Deposition of sediments on mudflats and sandflats ......................... 103
6.2.
Species in the Cummeen Strand/Drumcliff Bay SAC ............................ 104
6.2.1. Marine mammal species listed for the SAC – Annex II species (EU
Habitats Directive) ........................................................................... 104
6.2.2. Fish species (Annex II) .................................................................... 104
6.2.3. Otter (Lutra lutra) (Annex II and IV) .................................................. 104
6.2.4. Marine mammals (Annex II and Annex IV) ....................................... 104
6.2.5. Other fish species ............................................................................ 105
6.3.
Mitigation for Cummeen Strand SPA .................................................... 105
6.3.1. Macrobenthos - food source for SPA bird species ........................... 105
6.3.2. Indirect Impacts on Natura sites in the wider locality, including Lough
Gill SAC .......................................................................................... 107
6.4.
Qualifying Species and Listed Species of Importance for the SPA ....... 107
7. CONCLUSIONS ................................................................................................... 108
7.1.
Cummeen Strand/Drumcliff Bay SAC (Site code: 000627) ................... 108
7.2.
Cummeen Strand SPA (Site code: 004035) ......................................... 108
7.3.
Lough Gill SAC (Site code: 001976) ..................................................... 109
8. ACKNOWLEDGEMENTS .................................................................................... 112
9. REFERENCES ..................................................................................................... 113
23
Contents
24
1.0
INTRODUCTION
1.1
PROJECT SUMMARY
Introduction
Sligo Harbour is the only working port, apart from Killybegs Fishery Harbour, between
Galway and Derry. It located in the estuary of the Garavogue River (sometimes written as
Garvogue or Garvoge) in Sligo Bay on the north west coast of Ireland.
At present, the harbour can accommodate ships with a maximum draft of 5.2 metres and
length of 100 metres, however the larger vessels that use the port can only pass through the
harbour to the quays at high spring tides, due to the shallow bathymetry of the navigation
channel and the harbour berths. At low spring tide, laden cargo vessels sit on the seabed
even at Deepwater Quay.
A training wall, the upstream 1,500m of which was recently refurbished 2007, reduces the
movement of sediment into the channel. Despite this, the shipping channel and jetty areas
have to be regularly maintenance dredged to remove siltation.
Within the Irish National Spatial Strategy 2002-2020, Sligo has been selected as a gateway
town because of its strategic location, physical capacity, infrastructure and its amenities
including water services. Sligo County Council is now proposing to dredge the harbour and
its channel with the aim of:
x Meeting the present and future demands of the tourism and transport industry.
x Promoting and improving facilities for marine leisure sector.
x Allowing the port to take account of business opportunities and increase marina
berthage.
x Enhancing the viability and environmental well-being of the area.
Sligo County Council is proposing to undertake a combination of maintenance dredging and
capital dredging within the harbour and its approach channel. Maintenance dredging from
Barytes Jetty to the Red Light is required to preserve the minimum required depth for current
vessels using Sligo Harbour. Capital dredging along the channel is also proposed to
generate new business, thereby securing the future viability of the harbour. A feasibility
study prepared by RPS Consulting Engineers in 2009 found that a depth of 3m below Chart
Datum was necessary to give a vessel of 4,500 dwt and a draft of 5.9m a 3 hour window of
opportunity for a 1 hour passage time to navigate the channel per tide, thereby securing
Sligo Harbour’s viability as a working port. In order to achieve this minimum requirement,
dredging a quantity of approximately 250,000m3 of material along the channel is considered
to be necessary.
This report documents the Environmental Impact Assessment (EIA) of the harbour dredging
scheme. The EIA has been carried out to ensure that the dredging is properly integrated with
the overall development of Sligo Harbour and that safeguards are put in place to protect and
maintain the natural environment.
1-1
1.2
Introduction
EXISTING PORT FACILITIES
The Port of Sligo extends from the Timber Jetty at Hyde Road Bridge for a distance of 1.3km
and formerly comprised a number of quays and jetties, namely:
x
x
x
x
x
x
Sligo Jetty,
Liverpool Jetty,
Barytes Jetty,
Deepwater Jetty,
Lynn’s Dock; and
Ballast Quay.
Only the Timber Jetty, the Barytes Jetty and the Deepwater Jetty have remained in service to
the present day. The main docking jetty is Deepwater Jetty, at the most westerly end of the
port. It and the Barytes jetty handle cargoes of coal, timber, fish meal and scrap metal and at
present around 25 ships per year dock in the harbour.
1.2.1.1 Improvement Works
Sligo County Council took over responsibility for Sligo Harbour from Sligo Harbour
Commissioners in June 2006. Since then Sligo County Council has embarked on a series of
improvement works which have included the refurbishment of the Deepwater Jetty in the
form of fendering and installation of safety items and the reinstatement of the Barytes Jetty,
which has been effectively rebuilt and which now functions as a much needed second
commercial facility. Improvements have also been made to the shipping channel training
wall.
The Deepwater Jetty is 77m long, the Barytes Jetty is 55m long and the harbour can
currently accommodate vessels of up to 3,500 DWT. The maximum draught for vessels is
currently 5.2m and the maximum length that can be accommodated is 100m.
The largest vessels that use the port can only pass through the harbour to the quays at high
spring tides due to the shallow water depths in the channel. At low spring tide, laden cargo
vessels sit on the seabed, even at Deepwater Quay.
Consequently, the shipping channel and jetty areas have to be regularly dredged to prevent
siltation. A training wall was constructed in order to hold back and reduce the movement of
sediment into the channel.
In the 1970s, problems regarding the storage of the silt led to the construction of a large
holding pond/bunded area (circa 6 hectares), westward of the Deepwater Jetty.
This area was filled with sediment in a major dredging operation (in 1985) and subsequent
maintenance dredging. The area is now completely filled and was developed in the late
2000s into the site for Sligo’s main wastewater treatment plant. As all of the remaining
intertidal area of Sligo Harbour has been designated as both a Special Area of Conservation
1-2
Introduction
and a Special Protection Area, bunding a further area of the foreshore for the containment of
dredged sediments is not considered to be a feasible option in the present day.
Maintenance dredging adjacent to the jetties is ideally required every year, and the disposal
of the dredged material will soon become a problem, as the former disposal area is no longer
available. Major capital dredging of the channel is urgently required.
In 2008 the Council also refurbished the Timber Jetty and installed pontoons for mooring
leisure craft. The new berthing pontoon installation at the Timber jetty is attracting small
fishing vessels and visiting yachts as their shallower draft allows them to navigate the
harbour entrance channel with fewer tidal restrictions.
The navigation channel upstream of Barytes Jetty is no longer used for commercial shipping
and so maintaining its depth is less critical. This section of the channel is therefore not
included in the current proposed dredging plans. However, the recently installed pontoon
berthing facility at the Timber Jetty is attracting visiting yachts and an acceptable minimum
depth will continue to be required in the future.
In the longer term, further improvement works are envisaged. These include:
x further extensions of the Timber Jetty pontoons;
x repairs to the bulk of the harbour wall from Deepwater Jetty to Silver Swan
development (city centre), to be done in sections;
x probable removal of Liverpool Jetty, which is broken;
x maintenance of the shipping channel and training wall;
x maintenance dredging of the shipping channel, as necessary.
A full description of the proposed dredging extents and depths is provided in Chapter 4
“Project Description”.
1-3
1.3
Introduction
STRATEGIC POLICY DRIVERS
Ireland has a planning policy framework that operates at European, National, Regional and
Local level. Planning authorities must recognise the key elements of the parent documents
in all decision making. The proposed dredging at Sligo is entirely consistent with the
strategic objectives at national, regional, county and local level as outlined in the review of
the following strategic policy drivers below:
1.3.1
National Policy
1.3.1.1 National Ports Policy Statement
The Government published the National Ports Policy Statement; the framework within which
the State’s commercial ports are expected to operate, in 2005. The core objective of the
National Ports Policy is to ensure investment in ports meets port capacity requirements and
to facilitate the availability of commercial port services which are effective, competitive and
cost efficient. The Harbours (Amendment) Act 2009 enacted many of the legislative changes
proposed by the Policy Statement. A review of the policy framework is currently being
undertaken, with a consultation document launched in September 2010.
The National Ports Policy Statement recognised that ports are essential pieces of national
infrastructure and as such have a strategic role in facilitating both national and regional
economic development.
When the 2005 report was published, there were 10 ports operating as commercial State
port companies and a further 13 harbour authorities (including Sligo) operating under the
Harbours Act 1946. The National Ports Policy Statement acknowledged that these smaller
harbours range from those with some commercial traffic to those that have experienced
gradual decline in terms of commercial and seaborne trade and exist only to service the local
economies that depend on them for seafishing and marine leisure. The Harbours Act 1946
was considered to be no longer appropriate governing legislation for these regional harbours
and a policy was put forward to transfer them to local control, where maximum utilisation and
benefit for the local regions can be realised. This is likely to be achieved by fully developing
the amenity value of these maritime facilities. To this end, the responsibility for Sligo
Harbour transferred from Sligo Harbour Commissioners to Sligo County Council in 2006 (S.I.
No. 316/2006 — Harbours Act, 1996 (Transfer of Sligo Harbour to Sligo County Council)
Order 2006). A number of improvements in the harbour have been carried out by the
Council since then to enhance its commercial and amenity value.
From 2005, Ireland’s ports as a whole have experienced both record traffic volumes, peaking
in 2007 and, more recently, sharp declines. The Ports Policy Statement focuses most of its
attention on the larger ports in Ireland and the challenges they face in light of a worldwide
shift towards containerised transport with larger ships requiring deep-water ports and the
reduced availability of smaller ships to serve local ports. There has also been a movement
from multi-cargo common user ports to specialist terminal-based ports such as Lift On-Lift Off
and Liquefied National Gas terminals. Whilst Sligo Port will never be able to receive large
1-4
Introduction
container vessels, there are a number of markets such as sea tourism charters and support
for the expanding energy industries such as wind energy, tidal current energy and gas
exploration and supply on the west coast which it may be able to expand.
The 2010 review provides insight into the role that smaller ports can play in transporting
goods. With increasing European trends towards charging for road use (e.g. tolls,
congestion charges) and increasing pressure on governments to implement policies to
reduce the amount of road freight transportation, the development and use of short sea
shipping routes is becoming increasingly important. Compared to road and air transport, rail
and sea transport are both regarded as being more sustainable modes. Sligo Harbour has
retained its rail link to the quays and as such has a significant advantage over several other
ports who have, over the years, removed their railway links. This makes the port ideally
placed to capitalise on EU investment programmes such as the Trans-European Transport
Network (TENs) and Marco Polo which provide funding for projects which shift freight
transport from the road to sea, rail and inland waterways.
1.3.1.2 National Development Plan 2007-2013
The National Development Plan Transforming Ireland – A Better Quality of Life for All
(hereafter NDP) was published in 2007. This document supersedes the National
Development Plan of 2000 to 2006 and notes that the Irish economy and society will undergo
a transformation almost as radical as the changes experienced in the past decade of growth
and development. This will be driven largely by the continuing increase in the population
which is projected to reach over five million by 2021.
One of the main aims of the NDP is developing the Gateways (see National Spatial
Strategy below). The key objective is to build on current trends and maintain strong and
sustainable growth in each of the Gateways over the period of the Plan with particular
emphasis on those with lower populations. Each Gateway therefore needs a clear vision of:
x Its future development strategy;
x The mechanisms to implement the strategy;
x Effective prioritisation of investment, both locally and centrally; and
x Accelerated delivery of critical elements of such investments.
The Plan provides for some €32.9 billion investment in transport generally. National and
international access will be central to the competitiveness of the Gateways. Key priorities will
be completion of the major interurban routes, the upgrade and enhancement of the public
transport network, improved port and airport access and investment in key secondary and
non-national roads between and within the Gateway regions.
By the end of the Plan, all the inter-urban routes between Dublin and the Gateways will have
been completed and many of the key inter-urban routes between Gateways, such as the
Atlantic Corridor, will also have been significantly upgraded. Investment in strategic nonnational roads within and between Gateways and their immediate hinterlands will also play a
key role in improving connectivity, circulation and facilitating the development of strategically
placed landbanks.
1-5
Introduction
Under the transport programme, some €481 million has been set aside for the ports subprogamme.
Of this, €450 will be spent on the major commercial ports; however €31 million has been
included in the Plan for investment in Regional Harbours. Following the establishment of the
commercial port companies, under the Harbours Act 1996, there remained thirteen regional
harbour authorities operating under the Harbours Act 1946. The Ports Policy Statement
stipulates that these regional harbours would best achieve their potential through transfer to
local authority or port company control and indeed by 2010 seven harbours had transferred
to relavant local control and one further harbour, Dingle, has been designated as a fishery
harbour centre. The Department continues to pursue the policy to transfer the five remaining
harbours to relevant local authority or port company control. These proposed transfers are at
various stages.
Sligo Harbour was transferred by Ministerial Order to Sligo County Council in June 2006. In
order to enhance the harbours during their transfer phase, a programme of remedial works
will continue to be funded, as appropriate, under this NDP. Exchequer funding has been
allocated for these remedial works over the period 2006-2009. These will be prioritised on
the basis of the protection of the fabric of the harbours. This expenditure is designed to
ensure that any undue financial burden is not placed on local authorities or ports companies
arising from the transfer of harbours. As part of the NDP and ports policy mid-term review in
2010 (Department of Transport, 2010) the issue of further funding for these harbours over
the remainder of the Plan was being considered. As of the time of writing, the Department of
Transport are still reviewing the submissions during made during the consultation period –
the revised policy statement will have to have regard to the changed economic and business
climate within which Irish ports currently operate.
1.3.1.3 The National Spatial Strategy 2002-2020
The Government’s ‘National Spatial Strategy’ (NSS) is intended to set a national context for
spatial planning which will inform Regional Planning Guidelines and strategies, as well as
County and City Development Plans and strategies. It is a twenty year planning framework
designed to achieve a better balance of social, economic, physical development and
population growth between regions. It aims to ensure high quality urban environments as
well as vibrant rural communities by strategically informing future investment to enable each
part of Ireland to achieve its potential.
It is a key infrastructural principal of the NSS that achievement of a spatial balance by
developing the potential of areas will depend on enhancing capacity for the movement of
people, goods, energy and information between different places.
In addition to initiating the process of preparing the National Spatial Strategy, the National
Development Plan (NDP) 2000-2006 identified the five main cities, Dublin, Cork, Limerick,
Galway and Waterford, as ‘Gateways’, or engines of regional and national growth. The NDP
1-6
Introduction
set the NSS the task of further developing the Government’s approach to achieving more
balanced regional development, including the identification of a limited number of additional
gateways. The National Spatial Strategy identified a further four national level gateways to
support the original five gateways; namely Dundalk, Sligo, and the "linked" gateways of
Letterkenny/Derry, and Athlone/Tullamore/Mullingar (Figure 1.1).
Figure 1.1: Border Region Relationships in terms of the NSS
The NSS states that critical mass in the West and North West “can be strengthened by
developing Sligo as a gateway to capitalise on its strategic location and energise its
associated hinterland. Building up the national role and scale of Sligo will require, as a first
step, the development of a planning, land use and transportation framework. This will provide
a focus around which local authorities, business and community interests can reach
consensus on the future development of Sligo and utilise its substantial physical capacity for
development, while safeguarding its outstanding natural setting.”
The NSS continues: the critical factor [for revitalising the West] is “underpinning the
sustainable development of strategically placed medium-sized towns to reinforce dynamic
rural economies. These economies will be based on the sustainable use of natural resources
such as scenic landscapes for tourism, the sea for fisheries and marine–based aquaculture,
the land for agriculture, forestry, inland aquaculture (in rivers and lakes) and renewable
energy. Appropriate investment in enterprise and local services will also be required to
sustain these economies.”
1-7
Introduction
The Strategy recognises an overdependence on Dublin Port inconsistent with the NSS policy
to promote balanced regional development. In accordance with this general policy, the NSS
identifies the ‘suggested solution [of] promoting alternative locations for some current and
future Dublin port activities, such as transit and storage of petrochemicals, bulk goods and
cars. More port business to and from various parts of the country through other nationally
strategic ports could be encouraged. This may require substantial investment in facilities at
alternative ports’ (p. 63).
Balanced regional development across the entire nation is central to the objectives of the
NSS. This means supporting the economic and social development of all regions in their
efforts to achieve their full potential by integrating strategic development frameworks for
regional development, rural communities, all-island co-operation, and for protection of the
environment with common economic and social goals.
Section 2 states that ‘marine and natural resources, including inland fisheries, sea fisheries,
aquaculture, forestry and mining, have an important role to play in providing sustainable
alternative sources of employment in rural areas’ (p. 19). It is considered that the strengths
of all rural areas must be identified and supported by an appropriate level of infrastructure
provision whilst ensuring a balanced approach to their potential for economic activity. The
Strategy considers that developments in marine and natural resources sectors offer
significant advantages for stable, long term economic activity in rural areas and coastal
communities, providing work for which many of the skills required are available locally.
The proposed dredging at Sligo harbour will safeguard the port’s future in terms of
commercial trade for further ten years or more. Sligo can capitalise on its existing strengths
as an employment centre for other towns in the surrounding area by building on the existing
facilities. Enhancement of the port’s navigability will therefore support the concept of
balanced regional development which is central to national policy objectives. The scheme
may enhance the employment opportunities in Sligo by providing better transport links for the
movement of goods and materials. This could have wider repercussions for the surrounding
rural hinterland thus improving the performance of the economy in Co. Sligo and the
northwest region as a whole.
1.3.1.4 Sustainable Development – A Strategy for Ireland (1997)
The National Sustainable Development Strategy, published in 1997, includes a number of
measures and actions relating to the conservation of the natural environment and the
protection of air and water quality. It aims to provide a comprehensive analysis and
framework which will allow sustainable development in Ireland. Although this document is
over ten years old, it remains relevant. A five-year review of the National Sustainable
Development Strategy entitled “Making Ireland's Development Sustainable”, was produced
by the Department of the Environment, Heritage and Local Government in 2002. A further
“Statement of Strategy 2008-2010” was published by the Department of Environment,
Heritage and Local Government in 2008.
Whilst cautioning that marine natural resource exploitation should be operated in a manner
which respects the environment, the Strategy notes that industry in Ireland has grown
1-8
Introduction
substantially since the 1960s. It is strongly export oriented with some 68% of manufacturing
jobs dependent upon exports at the time of the Strategy’s publication. The Strategy also
notes that at the time of publication it was estimated that ‘some 80% of all goods produced in
the world are transported by sea’ (p. 66). While the Strategy highlights that all modes of
‘transport have an extensive impact on the environment… there is no real alternative to road
transport for the vast bulk of goods movement’ (p. 106).
Additionally, it states that ‘sustainable industrial development must allow industry to pursue
its primary functions of generating wealth and employment while minimising impacts on the
environment’ (p. 87). While our natural assets are recognised as highly important especially
in terms of competing on an international scale, there is also recognition that industrial
development in a sustainable manner is needed in order to ensure continued economic
growth in areas.
Measures to mitigate any potential impact on the environment as a result of the proposed
development are outlined in the relevant sections of this Report.
1.3.2
Regional/Local Policy
1.3.2.1 Regional Planning Guidelines for the Border Region
The Border Regional Authority covers the counties of Cavan, Donegal, Leitrim, Louth,
Monaghan and Sligo, situated along the southern side of the border with Northern Ireland. It
is one of eight Regional Authorities established in 1994 to provide a regional tier of
government level in Ireland. The aim of the Authority is to achieve sustainable, balanced
regional growth and development whilst ensuring that quality of life, the environment and the
unique culture and heritage of the area are protected and enhanced. The function of the
Authority is to promote the co-ordination of the provision of public services at regional level.
The 2nd Regional Planning Guidelines 2010-2022 were adopted on the 29th September,
2010. The Guidelines form a long term strategic planning document which aims to direct the
future growth of the Border Region and seeks to implement the planning framework set out in
the National Spatial Strategy (NSS) published in 2002.
The new Guidelines also provide a more integrated model for the growth and development of
the Region, as spatial planning has been closely aligned with the economy and proposed
infrastructure within all relevant sectoral areas. This new approach has been complimented
by more detailed consideration given to areas such as climate change, environmental
management and flood risk management, all of which pose significant challenges for policy
makers.
The Guidelines state: “all ports within the Region are a significant asset and provide for the
efficient movement of goods for import and export.... the Border Regional Authority considers
it necessary that a ports strategy is developed for all ports on the island of Ireland, and in
particular, for the entire eastern seaboard of the island. The development and promotion of
1-9
Introduction
port activities will contribute to a modal shift from cars and decrease reliance on imported
fossil fuel.”
The guidelines further recognise that “Sligo Port has significant potential along the western
seaboard, but all options and proposed land uses should be considered with respect to its
future existence”.
The aims of Policy INFP14 are to “Support the provision of adequate port facilities for
commercial, fishing and amenity purposes within the Region, subject to compliance with the
Habitats Directive”
1.3.2.2 Sligo and Environs Development Plan 2010 - 2016
On 2nd November 2009, Sligo Borough Council and Sligo County Council adopted the Sligo
and Environs Development Plan 2010–2016. The Plan covers the Borough of Sligo together
with its urban and rural environs located outside the Borough, under the jurisdiction of Sligo
County Council. The SEDP 2010–2016 became operational on 30 November 2009 and will
remain in force for six years.
The Sligo and Environs Development Plan 2010 - 2016 includes a range of policies and
objectives that take into account the operations of and activities at Sligo Port.
As part of its Spatial Strategy, the Plan indicates that the Zoning Objective PF – Port
Facilities and Related Uses is to “Retain the port as a viable infrastructural and commercial
entity, supported by port-related industries and/or business activities”.
The Sligo and Environs Development Plan 2004-2010 also includes a range of policies and
objectives relating to an area obviously larger than the lands transferred from the Harbour
Commissioners. This area was referred to as “the Docklands”, “the Port” or “the Harbour”.
In 2006-2007 it became evident that piecemeal development was not a good option.
Instead, a comprehensive redevelopment framework should be prepared for a clearly defined
area, which would encompass the Port/Docklands/Harbour as well as other lands that are
underutilised, derelict, possibly contaminated, or are critical for the future provision of
essential infrastructure and various other facilities.
The Sligo and Environs Development Plan 2010-2016 (SEDP) identifies five areas suitable
for planned urban extensions, one of which is the Docklands and surrounding area located
between the Inner Relief Road, Strandhill Road and the sea shore.
The Spatial Strategy (Chapter 5 of the SEDP) makes provision for the preparation of a local
area plan for the Docklands, while the detailed policy sections include a variety of policies
and objectives directly or indirectly applicable to the Docklands area. The main specific
proposals included in the SEDP are:
x
retention of the Port as a valuable piece of commercial/industrial infrastructure;
x
reduction in the area reserved for port-related activities;
1-10
Introduction
x
remediation of the former landfill and other potentially contaminated lands;
x
revised street/road layout and improved connectivity with the city centre via
pedestrian-friendly crossings of the Inner Relief Road;
x
extended mixed-use zoning, including both retail and non-retail uses;
x
more land reserved for housing and a relocated neighbourhood centre;
x
enhanced provision of open space in the form of linear parks and cycle/pedestrian
routes;
x
support for the regeneration of the Sligo Docklands through the provision of a cultural
landmark building and the innovative reuse of former industrial buildings located in
the area as workspace for creative enterprises and new community uses.
x
In relation to Effective Transport and Movement, the Development Plan notes that,
while the significance of the Port in national terms is relatively low, it remains
important in the local and regional economy, supporting local industry and providing a
sustainable transport mode for imports and exports.
The Docklands “proper” area, i.e. lands immediately adjoining the waterfront, is currently a
run-down, visually unattractive enclave in one of the most visible locations of Sligo City. It is
considered that the redevelopment of the former docks should be undertaken in conjunction
with that of adjoining areas
It is the aim of the local authorities to encourage a significant shift from travelling by car to
other modes of transport and, in this respect, sets out their public transport policies that
include: Encourage the maximization of freight transport by rail and through the port (P-PT6).
1.3.2.3 Proposed Docklands Local Area Plan (LAP)
In February 2008, the DoEHLG recommended that the Sligo local authorities “harness all the
powers” of the new SEDP to secure the redevelopment of key areas such as the Docklands.
Having recognised the strategic nature of the Harbour and surrounding lands in their Sligo
and Environs Development Plan 2010-2016, Sligo Local Authorities indicated that they
wished to plan the redevelopment of this key area of the Gateway on the basis of a detailed
Local Area Plan (LAP). The formal LAP preparation has now commenced, with a pre-draft
consultation document having been released in 2011.
This paper has set out the broad scope of what could be achieved at Sligo and gives
examples of other coastal cities which have undergone significant regeneration of their
docklands. The purpose of the paper is to provide the public and other stakeholders with
sufficient information and suggestions to stimulate a debate on the future of the area. The
paper offers background information relating to the docklands and outlines the main
challenges that the LAP must address, such as meeting the requirements of the Habitats
Directive, in order to help transform the area into a vibrant urban quarter. The consultation
period ended in April 2011 and Sligo Council are now considering the submissions for
inclusion into the plan.
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Introduction
The pre-draft consultation notes that the proximity to the city centre, the waterfront along the
Garavogue Estuary, the unparalleled views of Benbulben, Knocknarea and the sea, the
variety of greenfield and brownfield lands with development potential all confer a special
character to the wider Docklands area.
It also argues that the Docklands LAP needs a clear vision of what it hopes to achieve, and
how this will bring benefits in the long term, if it is to be effective in regenerating the area.
A key issue raised within the draft consultation paper is the future vision of the port in the
context of its location at the centre of the city. The consultation paper asks whether the
commercial port operations need to be retained and enhanced or are best moved away from
their traditional location to an area where cargo handling would be more efficient. These
issues will be discussed further later in this Chapter and it is clear that retaining and
enhancing the port’s trade is of utmost importance to the economy of the area and that there
are no viable alternative locations for these activities.
Almost 40 submissions were received in response to the consultation paper, including one
from the Harbour Office which is reproduced in Appendix 1A.
The key port-related points raised in the submissions included:
x
The container railhead is a major landholding and strategic land bank. Its future
development is important for the overall area (IDA)
x
There should be provision for cargo transhipment zone within the docklands. Need to
think of a ship/rail/road freight hub as well as a train/bus hub. A tidal lock gate, like at
Kilrush, should be constructed for a marina (Des McConville)
x
Seek the protection and promotion of Sligo’s maritime heritage (Auriel Robinson)
x
Marine leisure should not be the only use for the port. Dredging of the port channel can
increase capacity at a cost of €5m. Silt-bed pollution test results support dredging
(Johnny Gogan)
x
More traffic could be generated if port dredging and widening took place. Either way,
commercial traffic would not constrain other uses and should be retained. Mooring rings
should be provided and rocks on the sea bed removed to eliminate possible damage as
boats fall with the tide. Expansion of the pontoon facility and the provision of services
should be a main feature of any redevelopment (Bryan Armstrong)
x
Commercial port activity must be retained and enhanced, as stated in the SEDP. There is
a complete lack of appreciation of the historical importance of Sligo Port. There appears
to be an agenda by Sligo County Council now the port has been taken over to cease to
fully recognise the importance of the port as a facility and generator of trade. SPBA fully
supports the proposed capital and maintenance dredging of sections of the navigation
channel as being essential for the port’s ongoing viability (Sligo Port Business Alliance)
x
A total of 150 plus persons are directly employed in the port area. It is estimated that
between 150 and 300 additional jobs rely on these businesses. There is clearly an
identifiable business community here, as demonstrated by the level of trade at Margarets’
Café on Finisklin Road. Any LAP must acknowledge this community. Sligo Port has also
evolved into a hub for the people of Sligo and includes activities such as refuelling
1-12
Introduction
vehicles, purchasing bulk fuels, bringing scrap metal and shopping for homeware. This
trade must be enhanced. Greenstar and Erin Recyclers Ltd. take exception to the manner
in which their businesses have been presented in the consultation paper. The brief
statement on ‘waste management’ is the only mention of the huge contribution that these
two companies make to Sligo Port in terms of services, trade and employment. Any
policies or objectives must take into account these existing land uses and protect these
businesses. Incompatible developments must not be allowed to locate adjacent to these
facilities (i.e. housing or office). (Existing Business Community)
x
Sligo Fuels Ltd. business plan envisages an increase in importation and distribution of oil
in bulk together with diversification into the importation, offloading, packaging and
distribution of solid fuels. Medium to long term strategy envisages an increased
proportion of these materials will be imported by sea. The company’s present road
delivery set up is expensive, disruptive and unsustainable. This will result in port usage
and also a larger storage depot. It is considered that the maintenance of the port and its
activity is a fundamental requirement of the proposed LAP. (Sligo Fuels Ltd)
x
The Chamber encourages a feasibility study for commercial rail linkage between the
railway station and the port prior to this link being severed. A rail corridor should be
preserved within the plan as there are too many examples where rail facilities were
removed only to be later regretted. Consideration should be afforded to the provision of a
marina within the plan. These have proven to be very popular in other locations and are
typically self-financing. They add to the ambience of an area and provide commercial
activity. (Sligo Chamber of Commerce)
As can be seen, the residents of communities connected or close to the Docklands, the
business people operating in the area and their customers, the potential users of future
amenities, the wider community, the artists and students of Sligo - all had the unique
opportunity to make a valuable input into the shaping of the Docklands’ future. Infrastructure
and service providers, state/semi-state bodies and funding agencies were also called to
contribute to the creation of a shared vision.
The extent of the LAP boundary will be decided following pre-draft consultation with the
public and the main stakeholders
1.3.2.4 Sligo County Development Plan 2005-2011
The role of the County Development Plan is to regulate, control and effectively promote
sustainable development in County. The Plan states the County Council's policies for land
use and for development control in its area.
Section 8.1.6. of the plan acknowledges that while the significance of Sligo Port in national
terms is quite low, it remains important in the regional and local economy, supporting local
industry and providing a sustainable import and export transportation facility.
As such, it outlines a number of key ports and harbours objectives:
x Continue to support the development and operation of Sligo Port.
1-13
x
x
x
x
Introduction
Improve road and rail access to the Port, in order to boost its viability as an international
freight port.
Assist Rosses Point Yacht Club and the local community in the development and
management of a local yacht haven facility, as resources become available.
Carry out improvement works on Coney Island Pier and at Raghly Harbour and maintain
and improve other piers and harbours, as resources allow.
Support the role of harbours, piers and shipways in facilitating fishing, marine leisure,
recreation and other activities.
However, the ports and harbours objectives must be set into the wider context of the Plan’s
coastal zone management and environmental objectives.
The plan recognises that the coastline is a finite resource that provides environmental,
economic, recreational and aesthetic benefits and access to marine resources such as
fisheries and aquaculture. It also contains many sensitive ecosystems, ranging from sand
dune systems to salt marshes and estuaries rich in marine and bird life and is significant in
terms of cultural and archaeological heritage. The plan acknowledges that the coastal zone
is under increasing pressure from issues such as coastal erosion, pollution and conflicting
user groups (eg fishermen, shellfish farmers, conservationists and tourism developers).
The objectives for fishing (6.2.2.1) include:
x Support and facilitate the development of the existing fishing industry.
x Encourage the expansion of sport fishing.
The objectives for mariculture (6.2.2.2) include:
x Encourage and facilitate mariculture development associated with job creation, in a
manner that is compatible with other uses of the Sligo coast.
x Work with the mariculture industry to increase environmental sustainability.
The objectives for nature conservation in the coastal areas (6.2.6.1)
x Support the management of sites of conservation importance, including pNHAs, cSACs
and SPAs.
x Take into account the potential conservation of all sites of interest within the coastal zone
when assessing development proposals.
x Promote the natural interest of the Sligo Coast as a sustainable tourism, conservation
and educational asset.
These are in addition to the more specific “Objectives for designated nature conservation
sites” (7.2.2.4) of which Sligo Harbour is one.
x
Maintain, and where possible enhance, the conservation value of all pNHAs, cSACs and
SPAs, as identified by the Minister for the Environment, Heritage and Local Government,
as well as any other sites that may be proposed for designation during the lifetime of this
Plan.
1-14
x
Introduction
Discourage development that would destroy or damage any sites of international or
national importance, designated for their wildlife/habitat significance, including pNHAs,
cSACs and SPAs.
The dredging scheme has been designed to maintain the aims of the development plan by
supporting local industry and boost viability as an international freight port whilst
safeguarding the interests of the local fishermen, shellfish producers and tourism developers
whilst providing the minimum possible impacts on the local conservation and heritage
designations. These aspects are discussed in more detail in Part III of this Report.
1.3.3 Other Relevant Policies
The proposed development would also support the objectives of the following national and
EU policies.
1.3.3.1 Transport Emissions
The EU’s climate and energy package contains specific measures aimed at addressing
emissions from transport. This reflects the fact that transport is responsible for around a
quarter of all EU greenhouse gas emissions, making it the second biggest greenhouse gas
emitting sector after power generation. Road transport alone contributes about one-fifth of
the EU's total emissions of carbon dioxide (CO2), and while emissions from other sectors are
generally falling, those from transport have increased 36% since 1990.
In addition to the legally binding target of 10% for renewable transport fuels in each member
state contained in the climate and energy package, the EU has also put in place a range of
policy instruments that are aimed at reducing GHG emissions from the road transport sector
in recent years. This includes targets to improve the fuel efficiency of vehicles, targets to
reduce the GHG intensity of transport fuels and the CO2 labelling of cars.
1.3.3.2 Irish Government Policy Initiatives
Climate change has also become a primary driver of policy in Ireland. The National Climate
Change Strategy 2007-2012, for example, contains a target to reduce greenhouse gases by
3% per year in an effort to meet Ireland’s commitments under the Kyoto Protocol, and of
course, Ireland is now legally obliged to meet the more stringent targets contained in the
EU’s climate and renewable package.
Recent estimates from the EPA indicate that after several years of very significant growth,
Ireland’s emissions actually declined in the last two years. However, it is also evident that
the majority of this decline is due to the economic downturn and it is expected that once
economic activity picks-up again, emissions will once again start rising. For this reason, it is
clear that concerted action will continue to be needed to “de-carbonise” the economy if
Ireland is to meet its international commitments.
In March 2007, the Government’s Energy White Paper was published. It sets out the
energy policy directions and targets for Ireland to 2020. It sets a target to achieve 20%
savings in energy end use across the electricity, transport and heating sectors by 2020, in
1-15
Introduction
line with EU targets, and an indicative target of 30% by 2020 to surpass the EU ambition. It
also sets a target for the penetration of renewable energy in transport – to account for 5.75%
of road transport by 2010 and 10% by 2020.
1.3.3.3 The Transport Sector – Irish Policy Initiatives
The transport sector will be expected to make a significant contribution to meeting EU and
national emission reduction targets. In 2009, the sector was responsible for over 21% of
Ireland’s total emissions and until recently, had seen amongst the fastest increase in
emissions of all sectors.
The National Climate Change Strategy 2007-2012 committed to changing the basis for
assessing Vehicle Registration Tax (VRT) and Motor Tax from 2008 so that they would be
more closely aligned with CO2 emissions and send the right “signals” to drivers. As a result,
both taxes are now levied on the basis of the CO2 emission rating of the car rather than
engine size as was the case in the past.
In line with the general shift in policy to ensure that motor taxes take greater account of CO2
emissions, in Budget 2010 the Government also announced the introduction of a carbon levy
on fossil fuels to change the relative price of fuels based on CO2 emissions in order to
change consumption patterns, encourage fuel efficiency and lead to an improvement in
environment quality. It is anticipated that the levy, which was introduced in December 2009
at a rate of €15 per tonne of carbon, will steadily increase in the coming years.
Sligo’s commercial port provides a net positive impact in terms of CO2 by reducing the road
haulage of goods handled at the port due to their bulk transport by shipping to and from the
North West region.
The Government’s Smarter Travel policy document, Smarter Travel: A Sustainable Transport
Future, was published in February 2009, which covers the period 2009-2020, highlights a
number of key steps to ensure that people choose more sustainable transport modes, to
minimize the impact of transport on the environment and to improve Ireland’s security of
energy supply by reducing dependency on imported fossil fuels.
1-16
1.4
PROJECT JUSTIFICATION
1.4.1
Background
Introduction
With a population of 17,568 (expanding to c.35,500 living within 10km of the city centre) in
2011 (CSO, 2012), Sligo is the largest urban centre in the North-West.
During the 17th and 18th centuries, Sligo Port established itself as an important focus of trade,
with good quantities of cattle, hides, butter, barley, oats, and oatmeal being exported and
with the city’s linen exports well established. Imports included wood, iron, maize and coal.
The town prospered due to the trade with wealthy merchants setting up homes along the
fashionable Castle Street and Radcliffe Street (later renamed Grattan Street). This wealth is
demonstrated by the construction of the Cathedral of John the Baptist, which was completed
as early as 1730. It was designed by Richard Cassels, the architect of many important
buildings at the time, such as Leinster House in Dublin and Russborough House in County
Wicklow. The most notable ship companies who operated out of Sligo included Sligo Steam
Navigation Company who introduced the first steamer in 1857, Messrs Middleton &
Pollexfen, Harper Cambell Ltd and the former Sligo Harbour Commissioners who owned a
number of dredgers used for maintenance of the Channel (McTernan, 1992).
Sligo Harbour is the most northerly commercial port on the west coast of Ireland. There are
two working jetties, Deepwater and Barytes which handle cargoes of coal, timber, fish meal
and scrap metal. Sligo County Council took over responsibility for Sligo Harbour from Sligo
Harbour Commissioners in June 2006. Since then Sligo County Council has embarked on a
series of improvement works including refurbishment of the Deepwater Jetty, reinstatement
of Barytes Jetty and improvements to the shipping channel training wall. The Deepwater
Jetty is 77m long and the Barytes Jetty is 55m long, allowing the harbour to accommodate
vessels of 3,500 DWT. The maximum draught for vessels is currently 5.2m and the
maximum length that can be accommodated is 100m. Most recently, the Council refurbished
the old Timber Jetty and installed pontoons for mooring leisure craft. The facility became
operational in November 2008.
Sligo County Council, in the interest of ensuring continued use of the existing facilities and to
improve operational opportunities in the port, now wishes to undertake the following works
within the harbour and its approaches:
x
Maintenance Dredging of the berths and navigation channel from the Barytes Jetty to
the Red Light is required in order to maintain the minimum required depth for current
vessels using Sligo Harbour. The siltation of the channel has begun to pose a
significant threat to navigational safety.
x
Capital dredging along lengths of the channel in order to generate new business and
thereby secure the future viability of Sligo Harbour as a destination for commercial
vessels.
In the operation phase, the dredging will permit vessels with a draft of up to 5.9m to access
the Barytes and Deepwater Jetties and improve the window for access. Additionally with the
1-17
Introduction
refurbishment of the Barytes jetty in 2008 the Port has increased the capacity of the facility
by being able to unload two vessels simultaneously which will contribute to an increase in
trade. The primary purpose of the dredging is to safeguard the existing trade at the port,
allow for its future expansion and to comply with health and safety requirements.
Sligo Harbour holds a number of important environmental designations including Special
Area of Conservation and Special Protection Area and therefore the EIA studies must include
an Appropriate Assessment which will fulfil the requirements of the Habitats Directive.
1.4.1.1 Works to Date
Following the Review of Regional Harbours and Ports carried out by KPMG Management
Consultants in 1999, which recommended the transfer of ownership of certain harbours to
local authorities, Sligo Port was transferred to Sligo County Council under Ministerial Order in
2006. There were approximately 90 acres of land under the control of the Harbour
Commissioners, most of which had been reclaimed from the sea since the 19th Century. In
2006 it was estimated that approximately 75 acres (36 properties) were leased for both portrelated and non-port-related purposes.
Funding was made available by the Department of Marine and Natural Resources
specifically for the takeover and was directed at Safety and Remedial issues. A total grant of
€1.85M was provided to carry out essential works. The works included the design and
construction of replacement commercial berthage at Barytes Jetty, new access and safety
facilities at Timber Jetty and substantial improvements to the training wall which helps
maintain the shipping channel to the port. In addition, the new pontoon facility at the Timber
Jetty gives opportunities to strengthen the recreational fishing and sea tourism activities in
Sligo, such as the establishment of a sea bus between Sligo and Rosses Point.
Maintenance dredging of the channel took place in 1998, while maintenance dredging of the
berths took place in May 2010.
A 60 metre pontoon was recently provided that can handle up to 10 vessels alongside if
some are tied up in parallel with each other.
1.4.1.2 Approach
The approach adopted for the business case study commissioned for this Report was as
follows:
x
A site visit was made and discussions with were held with the Harbour Master and
other officials in relation to commercial, marine tourism and other business related
activities, employment, ship movements and trends at Sligo Port
x
Telephone discussions were held with the Port’s principal commercial customers
x
All relevant traffic, financial and commercial data including port charges and operating
and maintenance costs were collected and analysed
1-18
x
Introduction
A report was prepared demonstrating the socio-economic importance of Sligo Port to
the city and region, excerpts of which have been incorporated into this Chapter.
1.4.2 Sligo Port
In this section, we examine the current activities in Sligo Port and present brief profiles of the
Port’s customers.
1.4.2.1 Port Volumes
Table 1.1 provides details of traffic volumes (‘000 Tonnes) for the major Irish ports including
Sligo Port for selected years between 1990 and 2010.
Figure 1.2 provides a graphic representation of national traffic volumes (‘000 Tonnes) for the
major Irish ports including Sligo Port for selected years between 1990 and 2010.
Figure 1.2: Irish Port Traffic
80
Sligo (000 Tonnes)
70
50,000
60
40,000
50
40
30,000
30
20,000
20
10,000
10
0
0
1987
1994
1997
2000
Sligo
2003
Republic
1-19
2006
2009
Republic (000 Tonnes)
60,000
Introduction
Table 1.1: Irish Port Traffic
‘000 Tonnes
1990
1995
2000
2005
2006
2007
2008
2009
2010
Belfast
7,757
10,144
12,484
13,500
13,514
13,416
13,040
12,050
12,827
Larne
4,001
4,673
4,508
5,496
5,488
5,464
5,166
4,297
4,609
Warrenpoint
1,413
1,683
1,676
2,436
2,307
1,999
2,118
1,841
2,327
Londonderry
730
1,044
1,189
1,150
1,689
1,934
1,840
1,619
1,757
Other NI
2,485
2,491
1,634
1,471
1,487
1,055
1,334
979
1,387
N IRELAND
16,386
20,035
21,491
24,053
24,485
23,868
23,498
20,786
22,907
Dublin
6,384
8,899
15,892
19,227
20,795
21,801
21,127
18,606
19,548
Shannon Foynes
5,933
8,061
10,282
11,355
11,393
11,072
10,819
7,577
9,134
Foynes
1,084
1,362
Cork
5,857
7,104
9,732
9,919
9,709
10,098
9,633
7,968
8,466
Waterford
1,328
1,776
1,943
2,257
2,376
2,253
2,082
1,631
1,451
New Ross
1,021
1,056
1,121
966
831
729
694
515
Rosslare
807
1,130
1,913
3,118
2,744
2,926
2,722
2,328
Drogheda
1,004
673
1,015
1,402
1,279
1,035
664
555
499
Greenore
491
300
444
649
869
790
700
390
503
Arklow
275
270
88
0
0
0
0
0
0
Dun Laoghaire
261
n/a
225
156
82
61
49
14
2
Dundalk
321
232
285
337
436
371
217
222
140
Wicklow
205
154
151
282
297
221
85
73
89
Galway
429
456
727
1,019
946
945
838
723
671
Sligo
32
32
37
35
43
46
41
53
54
1,198
1,142
1,191
1,402
1,009
933
1,224
344
Bantry
444
2,502
Other R of I
641
875
220
282
327
389
401
292
REPUBLIC
26,073
32,380
45,273
52,146
53,318
54,139
51,081
41,880
45,071
ISLAND
42,459
52,415
66,764
76,199
77,803
78,007
74,579
62,666
67,978
Source: CSO
1.4.2.2 Tonnage and Vessel Numbers
Table 1.2 and Figure 1.3 present details of vessel numbers and tonnage per vessel between
2000 and 2011. It can be seen that tonnage per vessel has been growing steadily such that it
1-20
Introduction
was 2,344 tonnes per vessel in 2011. Table 1.3 provides a more detailed breakdown for the
period 2008 – 2011 based on the harbour’s own records.
Table 1.2: Sligo Port Traffic
2000
2002
2004
2005
2006
2007
2008
2009
2010
2011
Tonnage
37,000
57,000
72,000
35,000
43,000
46,000
41,000
53,000
52,000
49,000
Vessel Numbers
28
37
35
21
22
24
22
25
24
21
Tonnes/Vessel
1,321
1,541
2,057
1,667
1,955
1,917
1,864
2,120
2,183
2,344
Sources: CSO and Sligo Port (2011)
Figure 1.3: Sligo Port Traffic
2,500
70
2,000
60
50
1,500
40
1,000
30
20
Tonnes per Vessel
Tonnage ('000) & Vessel Numbers
80
500
10
0
0
2000
2001
2002
2003
2004
Tonnage
2005
2006
2007
Vessel Numbers
2008
2009
2010
2011
Tonnes/Vessel
Table 1.3: Sligo Port 2008 - 2011 Traffic Details
Company
Product
Import/Export
2008
2009
2010
2011
Hunter
Coal
Import
12,724
20,700
15,361
14,150
Arigna Fuels
Coal Products
Import
4,814
9,117
15,301
14,281
Erin Recyclers
Scrap
Export
21,203
13,752
19,021
20,796
Fish Industries
Fish Meal
Import
5,119
7,204
2,697
0
Brooks
Timber
Import
4,098
0
0
0
Emerald Salvage
Scrap
Export
4,475
2,673
0
0
Coillte
Logs
Export
0
1,793
0
0
52,433
55,239
52,380
49,227
TOTAL
Source: Sligo Harbour
It can be seen that timber was last imported in October 2008 and that there were no fishmeal
imports in 2011.
1.4.2.3 Freight Traffic Analysis - 2010
Table 1.4 provides more detail on the Port’s traffic in 2010 and 2011 respectively.
1-21
Introduction
Table 1.4: Sligo Port 2010 and 2011 Traffic Details
2010
Freight Type
Customer
No of Ships
Tonnage
Tonnage per Vessel
12
30,662
2,555
10
19,021
1,902
2
2,697
1,349
24
52,380
2,183
No of Ships
Tonnage
Tonnage per Vessel
11
28,431
2,584
10
20,796
2,080
21
49,227
2,344
Hunters, Arigna
Coal
Fuels
Scrap
Erin Recyclers
United
Fish
Fishmeal
Industries
Total
2011
Freight Type
Customer
Hunters, Arigna
Coal
Fuels
Scrap
Erin Recyclers
Total
Source: Sligo Harbour
1.4.2.4 Financial Performance - 2011
The Port charges €1,300 for Tonnage and €1 per tonne cargo dues for all good other that
scrap that is charged at €0.90 per tonne.
The estate is about 90 acres in size with much of the property leased out on long-term leases
with no rent reviews.
Total revenue in 2011 was of the order of €250,000 comprising €65,000 from shipping
tonnage and cargo dues, €185,000 from leases and the balance from earnings from the
pontoon.
Budgeted income in 2012 is estimated at €285,000.
Costs include an annual charge of €4,800 for the foreshore lease as well as the salaries of
the Harbour Master, part-time secretary and Council engineering staff allotted to port
activities.
1.4.3
Customers
1.4.3.1 Arigna Fuels
Arigna Fuels is located in Carrick-on-Shannon in the valley of Arigna on the border of the
counties Leitrim and Roscommon some 26 miles from Sligo. Arigna Fuels was established to
focus on the development of low smoke and smokeless fuels (coals), with the aim of
protecting the environment in Ireland.
1-22
Introduction
Slack is imported from Swansea and is processed into smokeless fuels.
While not employing any staff at Sligo, the company employs 50 in bagging and there would
be 20 hauliers engaged in collecting the slack and in transporting the end product to
customers. Some of the product is exported to Scotland and elsewhere in Britain.
Total imports in 2010 were some 70,000 tonnes of which about 20,000 tonnes came through
Sligo. The reduction in water depth and weather concerns have resulted in the loss of a
number of cargoes, of the order of 9,000 tonnes, to Sligo because of the reduced window for
docking with diversions to Belfast and Derry. These diversions resulted in an extra cost to
Arigna of some €3 per tonne.
The company sees the importance of Sligo Port being able to take 3,500 tonne vessels
safely.
1.4.3.2 Hunters (Bord na Mona) Ltd
Hunters import coal from Poland, Rotterdam and Scotland, with nuggets from Germany
through Rotterdam. The product is distributed locally to wholesalers and co-ops.
The company acts as agent and stevedore, and employs about nine in total including a crane
operator and with five staff in the yard. There would also be a number of hauliers that would
transport the coal to customers.
Should Sligo Harbour close, then the local facility would also close.
1.4.3.3 Erin Recyclers Ltd
Erin Recyclers Ltd. is one of Ireland's leading independent Scrap Metal Recycler providing
collection, sorting, processing and crushing services on a nationwide all-Ireland basis for all
types of scrap metal waste including ferrous and non-ferrous metal, End of Life Vehicles
(ELVs), Car Shells, Lead Acid Batteries, Electrical Cables and WEEE.
The company has two modern fully waste permitted scrap yard facilities strategically
positioned at Sligo Harbour and its sister company Foyle Recyclers located at Derry Port.
In 2010, almost 17,000 tonnes of scrap steel were exported through Sligo while an additional
12,000 tonnes of car bales were exported through Belfast at an extra transport cost of some
€300,000. It is expected that the car bales will be exported through Sligo Harbour in 2011
with a potential eight extra ship movements.
The company uses 2,500 tonne vessels.
The company employs 30 directly and 40 indirectly.
1.4.3.4 United Fish Industries Ltd
United Fish Industries Ltd. located at Killybegs, imported fishmeal into Sligo from Rotterdam
for Skretting in Westport. Unfortunately, this company closed in late 2010. In addition, with
1-23
Introduction
the reduction in fish quotas, including those for blue whiting, these events will now impact on
future imports through Sligo. In 2011, there were no loads imported through Sligo.
Employing some 20/25 on a seasonal basis at Killybegs, the company does not employ any
staff at Sligo but would send some of their workers down to Sligo when a ship unloads its
product there that would be stored at the Gallaghers site. Any other imports are imported
through Larne.
1.4.3.5 Sea Angling
There are three charter vessels operating primarily from Sligo Harbour and Rosses Point that
are available for hire for sightseeing, sea angling, eco-tourism, seal watching trips etc and
trips to Inishmurray Island, Coney island and elsewhere. Tourists come from all around
Ireland, the UK and mainland Europe. The charterers also provide any necessary tackle.
All-day trips as well as evening trips are offered during the summer at a cost of the order of
up to €40/€50 per head.
At least 5,000 visitors have used this service in recent years, although there has been a
reduction in visitor numbers due to the economic recession.
Two of the charterers are members of Irish Angling Charters/North West Charter Skippers
Association, http://www.irishanglingcharters.ie/ - this site gives additional details of the
services offered. One of the charter skippers is also the Harbour Pilot.
While the pontoon at Sligo Harbour is welcomed, it is suggested that there should be another
pontoon at Rosses Point as it would reduce the travel time off the sea journeys. It would also
address possible safety issues in accessing boats that are moored off other boats at the
Harbour pontoon.
1.4.3.6 Fishing Boats
No fishing boats operate from Sligo Port.
1.4.4 Economic Impact
In this section the economic impact of Sligo Harbour will be considered.
The overall impact of Sligo Harbour’s activities may be separated into three parts as follows:
x
The Direct Impacts give the total expenditure on the purchase of goods and services by
Sligo Harbour and other businesses at the Port
x
Indirect Impacts are those which occur when local suppliers in receipt of expenditure, in
turn purchase goods and services. This in turn results in further production and
employment in businesses located in the country.
x
Induced Impacts relate to the re-spending of household incomes derived from the
additional employment generated through the indirect impacts described above. This
expenditure in turn accrues to households, businesses and the government and some
leaks out as imports. Thus, the knock-on impacts throughout the economy arising from
1-24
Introduction
the direct expenditures result in a higher overall impact than is suggested by the initial
round of direct expenditures.
The overall impact is the sum of the direct, indirect and induced impacts. These impacts may
be quantified in terms of expenditure and employment. This overall impact can then be
measured as a multiple of the direct impact of business. Thus, expenditure and employment
"multipliers" encapsulate the impact of the business in the country, and is estimated to be of
the order of 1.8 for port-related business.
1.4.4.1 Employment associated with Harbour Activity
The total employment, full-time and part-time, associated with the Harbour’s activity is of the
order of 180 made up as follows (Table 1.5):
Table 1.5: Employment associated with Harbour Activity
Sligo Harbour
Sligo Harbour Company
4
Hunters
9
Arigna
0
Erin Recyclers
30
Fish Industries
0
Marine Tourism
3
TOTAL
46
Elsewhere
Indirect
50
20
40
25
75
60
According to the submission by the Existing Business Community in relation to the
Docklands LAP (refer to Section 1.3.2.3), a total of 150 plus persons are directly employed in
the port area and that between 150 and 300 additional jobs rely on these businesses. Many
of these jobs could be impacted by the closure of the Harbour.
1.4.4.2 Disposable Income
Applying the average industrial salary of €36,000 to the FTEs based in the Harbour (46) and
applying an Employment Multiplier of 1.8 to take account of indirect and induced employment
effects, the total gross salary income is of the order of €3 million.
The net disposable income, after tax, PRSI and Universal Social Charge deductions totalling
some 30 per cent, is €2.1 million.
This sum is likely to be under-estimated as it is probable that the average income is greater
that the average industrial wage and the numbers overall benefiting from harbour activity is
larger than that estimated.
1.4.4.3 Gross Value Added
Gross Value Added (GVA) is a measure of the value of the goods and services produced in a
region and, as such, it represents the overall contribution to the Gross Domestic Product
(GDP) of the Irish economy.
1-25
Introduction
Its determination can be used to estimate the value of the economic output linked to jobs
directly associated with Sligo Harbour.
The CSO publishes GVA values per employee and was of the order of €58,000 per worker
for the Border Region in 20081.
Using that value per worker, the GVA associated with Sligo Harbour is of the order of €4.8
million.
1.4.4.4 Value of Throughput
The value at cost of the freight through the port in 2011, nett of taxes and freight costs, is
estimated at some €8.5 million.
1.4.4.5 Maritime Tourism
There is general consensus that harbours and marinas have a tourism and economic benefit
for the towns where they are sited:
x
Maritime tourism is a major instrument of regional development. Many tourism
enterprises are situated in areas where other employment options are limited.
x
Local communities benefit from investment in facilities for tourists such as leisure and
sporting facilities and in associated infrastructure including access transport and roads.
x
A vibrant tourism industry contributes to the viability and sustainability of a wide range of
local enterprises.
x
Tourism promotes an enhanced awareness and positive appreciation of local traditions,
way of life and cultural heritage
Specifically, tourist expenditure creates both temporary employment and income from the
purchase of local goods and services. Service-type jobs are created in shops, gift
production, and restaurants and hotels. There is also a multiplier effect where the income or
wages generated from tourism is spent by residents on local services.
Research suggests that the average visitor to an Irish marina contributes about €140 to the
local economy. Whether the marina is occupied by a yacht owner, a visitor or a berth owner,
local businesses will benefit from the purchases of fuel, supplies and gifts. Chandler
purchases and any repairs carried out will also contribute to the local economy. Most users
of a marina will spend money in a town on visitor attractions, golf, meals, drink and other
day-to-day requirements, and all of this spend will boost the local economy which will have a
significant impact on employment and local disposable income.
The British Marine Federation estimates that visiting boats to UK marinas contribute on
average £150 each per night to the local economy. The BMF has also reported that for
every £ spend on boating, there is an associated spend of £6 onshore.
1
County Incomes and Regional GDP, CSO, 17 February 2011
1-26
Introduction
In the Republic of Ireland, it is estimated that for every Euro spent by an out-of-state tourist,
26 cent eventually ends up with the government through VAT, excise duty, PAYE etc. For
every €1 million of foreign and domestic tourism revenue, there is generated an overall GNP
impact of almost €680,000. Over 80 cent in every Euro of tourism spend remains in Ireland.
A survey of businesses in Dún Laoghaire and Malahide carried out by an Irish Sea Interreg
project found that marinas in both towns had a positive impact on 37 per cent of
respondents. At Kilmore Quay, some 67 per cent of businesses surveyed believed that their
local marina contributed to their success.
Whether the marina is occupied by a yacht owner, a visitor or a berth owner, local
businesses benefit from the purchases of fuel, supplies and gifts. Chandler purchases and
any repairs carried out will also contribute to the local economy. Most users of the marina
will spend money in the town on visitor attractions, golf, meals, drink and other day-to-day
requirements, and all of this spend will boost the local economy which will have a significant
impact on employment and local disposable income.
1.4.5 The Economic Impact arising from Construction
Construction is one of the most labour-intensive forms of economic activity in the Irish
economy. In 2006, it was estimated by Government that one quarter of all small and medium
sized enterprises (SMEs) in Ireland were in the construction industry.
There are many economic benefits that will arise from the construction of the new harbour
development. The benefits can be considered under three separate impacts:
x
the direct addition to economic output generated by the output of the industry; this can
be measured by the earnings of those employed in construction, i.e. payroll plus profits
earned. This comprises the employment generated by all jobs created by construction
firms that work directly on projects
x
the indirect employment generated by the firms that provide the inputs to the project in
question plus the employment generated by those firms who supply the firms providing
the inputs and so on. These are sometimes called ‘second generation’ suppliers and
include, for example, persons employed in concrete manufacturing, joinery workshops
and steel fabrication. Estimates of indirect employment in construction are typically
estimated at 40 per cent of direct employment, implying that for every ten persons directly
employed on a construction project there are a further four ‘indirectly’ employed in
supporting industries
x
the induced employment impacts which include all of the jobs created by those directly
and indirectly employed in construction spending their wages and profits throughout the
wider economy. These would include the additional jobs (and income) in retail and other
sectors that are created as a result of the various consumer purchases made by those
households employed at the direct and indirect stages. Our estimate for the induced
multiplier is 1.4
1-27
Introduction
In a submission2 to Government prepared by DKM for the Construction Industry Council, the
authors found that of the order of nine direct and indirect jobs were created for each €1
million of construction spend in 2007. With reduced tender prices now prevailing, DKM
suggests that the number of construction jobs per €1 million is of the order of eleven
excluding the induced multiplier effect. The actual labour intensity of construction projects, of
course, varies depending on the type of constructed being carried out.
According to the CIF, every €10 million invested in construction projects returns over €3
million to the Exchequer in VAT and Income Tax, excluding any Corporation Tax receipts.
1.4.6 The Positive Impact of Development
The proposed dredging will avoid a number of consequences. Some of those are listed
below.
1.4.6.1 Retention of Local Employment
The closure of the Port would result in a reduction in the number of people employed in portrelated activities and probably the closure of a number of local companies.
Based on our estimates above, if all of the directly related employment were to cease, at
least €2 million of disposable income would be lost to Sligo Town and its environs that would
have a major impact on local retailers, restaurants and the like. Further, given the current
levels of unemployment, it is likely that not all of those made redundant would find alternative
employment.
Those who could not find employment would be entitled to social assistance that would be a
cost to the Exchequer which, ultimately, will be funding the dredging.
1.4.6.2 Maintenance of Port Revenues and Lease Income
Closure of the Port would mean that the Council would no longer generate harbour income
for tonnage and cargo dues. In addition, a likely result would be a number of tenants leaving
the harbour site, which would impact on the Council’s lease income.
1.4.6.3 Avoidance of Extra Transport Costs
The diversion of freight to alternative ports, e.g., Galway, Derry and Killybegs, would result in
extra freight traffic on our roads in bringing the goods to Sligo. The extra transport costs are
estimated at almost €2 per mile,
1.4.6.4 Reduction in Carbon Footprint
The additional road traffic would add to the carbon footprint from the additional transport
emissions, would lead to increased health risks and the incidence of accidents and fatalities,
and generate greater traffic congestion and extra travel times. Already, over 30 per cent of
transport greenhouse gas emissions are from the freight sector. Statistics from the UK
2
Submission To The Government by the Construction Industry Council: Jobs and Infrastructure – A Plan For National
Recovery, DKM Economic Consultants and Goodbody Corporate Finance, March 2009
1-28
Introduction
Department of Energy and Climate Change indicate that every extra kilometre of travel by a
Heavy Goods Vehicle generates 0.9 kilograms of Greenhouse Gas in terms of CO2, CH4 and
NO2. The consequences of the additional road traffic run contrary to Government objectives
laid down in its document “Smarter Travel – A Sustainable Future; A New Transport Policy
for Ireland 2009 – 2020”.
1.4.6.5 Growth in Marine Tourism
A failure to maintain the harbour and provide a working environment would affect its
attractiveness for marine tourism.
1.4.6.6 An Improved Image
A working harbour can be a major attraction. A closed harbour can be an eyesore. It is
probable that a failure to maintain the port area would result in it becoming a derelict site with
all of the consequent problems that such a site can become.
1.4.7 Conclusion
The city of Sligo has been designated as one of four National Level Gateways under the
National Spatial Strategy and, as such, plays an important role in the economic life of the
region and country. As a Gateway, it is important that it offers and provides transport links for
all modes of transport.
The Regional Planning Guidelines for the Border Region note that Sligo Port has significant
potential along the western seaboard. This support is echoed in the Sligo and Environs
Development Plan 2010 - 2016 that points out that, while the significance of the Port in
national terms is relatively low, it remains important in the local and regional economy,
supporting local industry and providing a sustainable transport mode for imports and exports.
The Development Plan has as a Zoning Objective ‘Retain the port as a viable infrastructural
and commercial entity, supported by port-related industries and/or business activities’.
Sligo Harbour enables the movement of bulk cargo by sea direct to and from Sligo and the
loss of such a facility would be a loss to the city, county and region given that Sligo Port is
the only commercial working harbour between Galway and Killybegs and Derry.
We argue that the proposed maintenance and capital dredging should proceed. Not only will
it facilitate the retention of existing business and be the basis for potential new harbour
business such as off-shore energy servicing, it will also protect local employment and retain
port revenue. In addition, it will also avoid:
x
the loss of employment that would arise, possibly up to 80 jobs
x
reduction in consequent spend in the city and environs – up to € 2 million annually
x
loss of tax income to the State and payment of social welfare to those who cannot find
alternative employment
x
loss of economic benefits arising from the construction phase in terms of employment
and local spend
x
loss of port revenues and certain lease income currently €250,000 in total per annum
1-29
Introduction
x
extra transport costs and journey times for those industries remaining
x
increased carbon emissions
x
higher incidence of accidents and fatalities
x
additional travel that would not be in accordance with the Government’s Policies on
Sustainable Transport and Climate Change
x
reduction in maritime tourism activity and spend
x
negative impact on image and profile of the city
The proposed development supports the Council’s own Public Transport Policy that states
‘Encourage the maximisation of freight transport by rail and through the port’.
Further, many of the submissions in relation to the Docklands Local Area Plan support the
development of the Port.
Our analysis suggests that the cost of the proposed dredging, some €5 million, would be
recouped by the State in a short number of years.
It is vitally important that maintenance dredging is carried out in the short term which
would have a cost estimate of €80,000 for 2012.
At a broader level, we therefore conclude that there is a business case for proceeding with
the proactive dredging of the channel.
1-30
1.5
Introduction
CONSIDERATION OF ALTERNATIVES
The consideration of alternatives in an important requirement of the Environmental Impact
Assessment (EIA) process. For the purposes of the EIA Regulations, alternatives may be
described at three levels:
x
Alternative Locations;
x
Alternative Designs;
x
Alternative Processes.
1.5.1
Alternative Locations
The port at Sligo Harbour is well established and has a long history of being a hub of activity
within the city. Indeed, Sligo began its development as a port of consequence for agricultural
goods to Britain and the Europe in the 13th century. Official records in the fifteenth century
mention ‘Fish Quay’ under Henry VI reign. Customs duties under the Harbour
Commissioners can be traced back to George II, in 1689. At that time and for two hundred
years thereafter, Sligo was the most important Port in the Northwest (Sligo County Council,
2008). During the time of the Great Famine, around 1847-1850, it is estimated that more
than 30,000 people emigrated through Sligo Port, mainly to Canada and the United States.
Sligo Harbour is sheltered from the storms of Donegal Bay and the Atlantic by the headlands
at Strandhill and Rosses Point and by Coney Island and Oyster Island. As a consequence,
the sand flats within the harbour have become important areas for bird life and the entire
harbour holds the European-level designations of Special Protection Area and Special Area
of Conservation. There is no feasible means of relocating the port elsewhere within the
harbour and although the container gantries at the port were removed in 2006, the port is still
capable of receiving bulk materials and general cargo and provides a valuable service to its
hinterland area.
The nearest harbour to Sligo capable of accepting commercial port traffic is Killybegs, Co.
Donegal, some 100km northwest by road. Killybegs is primarily a fishing port, although its
recent upgrade and redevelopment in 2006 have allowed it to expand its trade into the import
and export of dry bulk, break bulk, fuels and general cargo including containers. Most of the
trade through Killybegs is directly related to the fishing industry, e.g. fishmeal. Killybegs is
constrained in the amount of goods it can distribute to its hinterland by its poor road
connections. Most of the industry at Killybegs is centred around processing of raw materials
landed on site and re-exporting the goods by sea. Up to two thirds of the fishmeal produced
at Killybegs is exported by sea.
Sligo County Council have stated that it is their intention to continue with the programme of
developing and enhancing the commercial and amenity value of the port which began when
1-31
Introduction
they took over responsibility for the port from Sligo Harbour Commissioners. In this respect
there are no suitable alternative locations where this development may take place.
1.5.2
Alternative Designs
The alignment and width of the proposed dredging have largely been determined by the
existing channel depths, the characteristics of the vessels which will use the port and current
guidelines on navigational safety.
The tide levels for Sligo Harbour (Oyster Island) are as follows:
Highest Astronomical Tide
Mean High Water Spring Tide
Mean High Water Neap Tide
Mean Low Water Neap Tide
Mean Low Water Spring Tide
Lowest Astronomical Tide
HAT
MHWS
MHWN
MLWN
MLWS
LAT
4.6m CD
4.1m CD
3.0m CD
1.5m CD
0.5m CD
-0.2m CD
Tide levels are established in relation to the Standard Port, Galway.
1.5.2.1 Channel Alignment
The alignment of the navigation channel is largely determined by existing physical
constraints. These include the training walls extending from Ballyweelin Point to the Barytes
Jetty, Oyster Island and various rock outcrops between Ballyweelin Point and Sligo Bay.
Field surveys undertaken during summer 2010 and winter 2010-11 have observed that the
training walls are important roosting areas for the bird life within Sligo Harbour SPA and
disturbance of the training walls might adversely impact the species which use them.
Realigning the navigation channel would also create increased dredging quantities and might
potentially cause changes to the tidal currents within the harbour, therefore alteration of the
route of the navigation channel is not being considered for this scheme.
The alignment of the proposed dredging of the channel will therefore follow the alignment of
the existing channel.
1.5.2.2 Vessel Characteristics
Through consultation with the Harbour Master from Sligo County Council the vessel
characteristics for the current and anticipated users of the port have been reviewed and the
following criteria will apply:
Vessel Characteristic
Length overall
Beam
Draft
Dead Weight Tonnage
Design Criteria
100m
17m
5.9m
4,500 tonne
1-32
Introduction
1.5.2.3 Channel Width
The design criteria for the channel cross section were based on the requirements of Sligo
County Council and the design guide produced by PIANC (The World Association for
Waterborne Transport Infrastructure).
The bottom width of the channel has been determined from the sum of the basic
manoeuvring lane plus the additional width to account for vessel speed, cross winds, cross
currents, longitudinal currents, wave height, aids to navigation, bottom surface, depth of
waterway plus an allowance for bank clearance. Having regard to the foregoing, a bottom
channel width of 50m is recommended.
The bed material is predominantly a fine silty sand with a relatively uniform grading. This
material is typically stable at side slopes of approximately 1 in 5 in still water conditions and
approximately 1 in 11 in active water conditions.
A stability analysis of the channel side slopes undertaken as part of RPS’ 2010 Feasibility
Study concluded that a slope of 1 in 7 should be provided which maintains a compromise of
pragmatic gradient whilst not over-stretching the dredging footprint.
1.5.2.4 Channel Depth
The following table (Table 1.6) illustrates the navigable period which will be available for a
range of dredged depths. Given the length of channel and the anticipated vessel speed, a 3
hour window of opportunity for a 1 hour passage time is considered to be adequate. The
costs of dredging to the various depths were also examined.
The bed level which has been chosen to accommodate the required size of vessel in the
port, allowing it sufficient navigation time whilst retaining cost effectiveness, is 3 metres
below Chart Datum.
Table 1.6 Comparison of Navigable Period with Dredged Depth
Dredged
Quantity
Depth
(approx)
Vessel Draft
3.0 m
4.0 m
5.0 m
6.0 m
Allow +10% for squat,
draught
&
sounding
uncertainties
and
initial
siltation
3.3 m
4.4 m
5.5 m
6.6 m
3
m CD
m
-0.5 m CD
0
2.8 hrs
N/A
N/A
N/A
-1.0 m CD
0
5.7 hrs
N/A
N/A
N/A
-1.5 m CD
25,000
7.3 hrs
2.0 hrs
N/A
N/A
-2.0 m CD
50,000
Navigable period in
8.6 hrs
5.1 hrs
N/A
N/A
-2.5 m CD
125,000
hours per tide (of 12.4
10.2 hrs
7.1 hrs
0.7 hrs
N/A
-3.0 m CD
250,000
hours)
12.4 hrs
8.3 hrs
4.6 hrs
N/A
-3.5 m CD
400,000
12.4 hrs
9.9 hrs
6.9 hrs
N/A
-4.0 m CD
550,000
12.4 hrs
12.4 hrs
8.1 hrs
4.0 hrs
-4.5 m CD
700,000
12.4 hrs
12.4 hrs
9.5 hrs
6.7 hrs
1-33
Introduction
1.5.2.5 Dredging Methodology
The material to be dredged is predominantly a silty sand which is expected to be suitable for
removal by a trailer suction dredger. Trailer suction dredging produces large quantities of
water with the dredged material. This excess water is either allowed to overflow the vessel
and return to the main body of water or it can be taken out to the disposal site together with
the dredged material. It is costly to take an excessive quantity of water to sea but this may
be necessary if dispersal of overspill creates undesirable levels of turbidity.
Dredging with hydraulic excavators is a slower process but reduces the amount of excess
water which is extracted. The slower rate of dredging with this system provides greater time
for the dispersal of supernatant water and reduces the level adverse affect there may be on
adjacent areas of seabed.
The dispersal of sediment plumes from the potential range of dredging activities is discussed
in Chapter 11 “Coastal Processes”.
1.5.3
Alternative Processes
As the port is located on an estuary, siltation of the berths and navigation channel is a
constant process, although construction of the training walls and their subsequent
refurbishment in 2007 has helped to reduce the annual rate of sedimentation. In the past,
large-scale maintenance dredging of the channel has taken place approximately once every
ten years with the most recent dredging taking place in 1998.
In the 1970s, problems regarding the disposal of the dredged material from maintenance
dredges led to the construction of a large holding pond/bunded area (circa 6 hectares),
westward of the Deepwater Jetty. This area was filled with sediment in a major dredging
operation (in 1985) and was used again during maintenance dredging in 1998. Now full, this
area was subsequently developed as the site for Sligo’s main wastewater treatment plant,
which was commissioned in 2009.
Small-scale dredging of the harbour berths takes place every two to four years, mainly by
plough dredging which redistributes the sediment rather than removing it, thus avoiding the
requirement to find an off-site disposal area. However, plough dredging is only a temporary
solution in between the larger scale maintenance dredging as it does not remove the excess
sediment from the area.
A Feasibility Study, prepared by RPS Consulting Engineers in 2010 (RPS, 2010), examined
the various options for disposing of or reusing the dredged material from this scheme.
In total, five disposal options of the dredged material were considered, in addition to the “do
nothing” scenario:
1-34
i)
ii)
iii)
iv)
v)
Introduction
Beneficial Re-use
Disposal on Land
Incineration
Reclamation within Sligo Harbour
Disposal at Sea
1.5.3.1 The “Do Nothing” Scenario
In the “do nothing” scenario, the natural process of siltation will continue within the navigation
channel. At present, commercial trade vessels can only enter the harbour on a spring tide
and when berthed the vessels rest on the bed for much of the tide. With continued siltation,
the harbour will become inaccessible even at spring tides and will no longer be able to be
served by commercial vessels. This trade will be lost to other ports and the businesses
which rely on the imports and exports into and out of the harbour will be forced to find
alternative means of transporting their goods. For this reason, the “do nothing” scenario is
not considered to be a viable option at Sligo Harbour.
1.5.3.2 Beneficial Re-use
The options for beneficial uses of fine materials are fairly limited. Historically, the main uses
for marine sediments from capital and maintenance dredging are:
x
x
x
x
land raising as part of port development;
land raising for other projects, for example housing;
land reclamation/capping;
flood and coast protection (above the level of mean high water springs).
Other potential uses such as brick manufacture and the addition of dredged materials as
aggregate filler in concrete or a raw material in cement manufacture have been investigated.
However, these uses are not currently considered to be viable markets for large volumes of
marine sediments from dredging, such as would be required at Sligo.
In order for the dredged sediment to fully meet the category for “beneficial reuse” (as
opposed to finding an alternative use for a waste product), a clear need for the sediment
must be demonstrated in advance of the project being progressed.
In the case of reuse for engineering projects or aggregate purposes, the sediment needs to
exhibit the correct geotechnical properties such as grain size, permeability and strength. At
Sligo, the proposed material to be dredged generally comprises a fine silty sand. Whilst this
material is chemically “clean”, the significant silt fraction makes the material physically
unsuitable for use on land as an engineering fill material, e.g. for raising land for housing or
for flood protection. The viability of using the sediments in other uses such as land
reclamation or capping is discussed in more detail in the sections below.
1-35
Introduction
In terms of coastal protection, in some areas dredged sediments can be used for beach
nourishment. Beach nourishment has occurred at a few locations within Ireland, but it
remains a relatively new concept. However, as with beneficial reuse on land, the physical
properties of the sediment are the key consideration in the sediment’s ability to be reused as
a resource. In general, it is a requirement for the grain size of the dredged sediments to
match the grain size on the beach to be renourished (CIRIA, 2010). Occasionally, slightly
coarser sediments are used, as these may stabilise the beach for longer periods of time.
At Sligo, the material to be dredged is too fine to be of any practical use as beach
nourishment. Fine material can sometimes be used for habitat creation purposes, such as
mudflat recharge or salt marsh restoration. However, these types of projects typically require
small quantities of sediment (e.g. 1,000m³-5,000m³) (UKMSAC, 2001) and there are no
areas near to the site which could accommodate anything approaching the volume of
sediment required to be removed at Sligo Harbour. Due to the diversity and abundance of
species which they support, mudflats and salt marsh areas are very often awarded
European-level environmental designations such as Special Protection Areas and Special
Areas of Conservation which creates additional levels of restriction on what sort of works can
take place in these areas. For these reasons there are no viable alternative beneficial uses
of the dredged sediment at Sligo Harbour.
1.5.3.3 Disposal on Land
General Landfill Option
This disposal option would require the dredger to bring the dredge spoil ashore, either by
barge or by pumping. The material would then be temporarily stored in a designated
hardstanding or lagoon area to allow for dewatering/drying, material classification and
leachate testing before subsequent transfer by road to a landfill site.
Even following a period of settlement, the dredged sediment would be likely to be considered
a wet material for the purposes of land-filling. Landfill space is in very short supply and it is
often the case that landfill sites are only licensed to receive relatively small volumes of wet
waste (e.g. 500m³) per week. At these rates, even if three landfill sites were to accept the
dredged material, it would still take over three years to transport all the material to landfill.
With an approximate specific gravity of 1.41t/m³ for 25% saturated silty sand, there would be
about 352,500 tonnes of dredge material to dispose of.
In order to be transported to a landfill, the material would be loaded into tipper trucks
(capacity 15 tonnes) or articulated lorries (capacity 30 tonnes). Assuming 100% loading, this
would generate the following number of return HGV trips:
x 30 tonne capacity 11,750 trips
x 15 tonne capacity 23,500 trips
There are no currently operating landfills that would be potentially able to accept all of this
material and the nearest landfill that could accommodate any of the material is approximately
1-36
Introduction
52km from Sligo. The four next nearest landfills with the potential to accommodate the waste
range from 70 to 130km one way distance from Sligo Harbour.
In addition to the transport costs, the waste material will be subject to Landfill Tax. In May
2011 the Minister for Environment announced that Landfill Tax will rise from €30 to €50 per
tonne from September 2011, increasing to €65 per tonne from July 2012 and €75 per tonne
from July 2013.
The material would also require a waste licence to permit disposal, which can take upwards
of a year to acquire, therefore it is realistic to assume that the 2013 tax rate will apply. In this
event, the tax alone to dispose of the material at landfill would be in excess of €26,000,000.
The gate fees and transportation costs would likely equal the tax costs to dispose of the
material at landfill, creating a total disposal cost in excess of €50million, an entirely
prohibitive cost.
For these reasons, disposal of the dredged sediments in landfill is not considered to be a
viable option.
Finisklin Option
A variation to the landfill option which has also been examined was the feasibility of placing
the material on the site of the former landfill at Finisklin, adjacent to the port. This option
seems attractive as the lands are immediately adjacent to the dredging area and the dredged
sediment could be pumped directly into a bunded lagoon on to the site where the
supernatant water would be able to drain back into the sea.
The landfill at Finisklin was in operation from 1958 to 1994. Following its closure, it was
covered and the site has largely remained disused since then. The precise boundary of the
landfill and the area filled as part of previous reclamation works is not fully known, however
the site is conservatively estimated as covering approximately 13 hectares (Malone
O’Regan, 2011). The access road to the new Sligo waste water treatment works crosses the
former landfill (Figure 1.4).
Following the closure of the landfill, the site was capped using imported fill, which varies in
thickness from a few centimetres to 2 metres. No specific capping design was undertaken
for the landfill at the time. It is estimated that approximately 625,000 tonnes of municipal
waste was placed in the landfill and a further 250,000 tonnes of capping material was
accepted.
At the time the landfill was initiated, none of the infrastructure that would be a compulsory
requirement under today’s legislation was installed, e.g. no landfill liner, leachate collection
system or gas collection, flaring or venting systems. The land reclamation process was
completed by depositing waste material directly on top of the existing mudflats and
progressively filling the estuary parallel to the shore.
In order to create a containment area for the dredged spoil, bunds would need to be
constructed around the edges of the two areas of the landfill shown in Figure 1.4. To
1-37
Introduction
successfully contain the wet material whilst still allowing the water to drain out, these bunds
would require to be in the order of 15 metres wide and 4 metres high.
Figure 1.4
Former Finisklin Landfill
Aerial photograph ESRI/Bing Maps © Microsoft Corporation 2012
Due to its central location in Sligo, the former landfill has the potential to be a valuable
commercial site. However, there are potential risks from landfill gas and escape of leachate
due to the lack of a formal engineering design at the time the landfill was commenced.
These issues must be addressed prior to any development being allowed to take place.
Sligo County Council recently commissioned consultants Malone O’Regan to undertake an
Environmental Assessment of the landfill which includes a risk assessment of the landfill.
The report makes a series of recommendations to reduce the risk to acceptable levels.
As part of the option evaluation, RPS met with engineers from Sligo County Council’s
Environmental Services Section and discussed the feasibility for the dredged material to be
placed on top of the landfill as additional capping with engineers from Malone O’Regan.
The Environmental Assessment Project (Malone O’Regan, 2011) has identified that the
greatest risk posed by the landfill is migration of landfill gas, which is currently unable to
escape in a controlled manner from the landfill. The report makes recommendations for the
construction of venting wells and trenches.
As already discussed, the landfill does not have a liner and the waste has been placed
directly on the original foreshore. A large (30m width crest) porous rock bund was
constructed to function as the outermost boundary of the former landfill (into Sligo Harbour).
The bund was designed to allow the free flow of the tide to and from the landfill at the time to
dilute and disperse the leachate. Leachate continues to visibly drain from the landfill into
1-38
Introduction
Sligo Harbour, however monitoring results from the Environmental Assessment Project
(Malone O’Regan, 2011) and Sligo County Council indicate that the leachate contents do not
currently exceed published leachate discharge guidelines and that the available assimilative
capacity within the receiving water is such that the leachate is not currently impacting the
water quality. However, the threat of contamination remains a high risk.
The placement of c.250,000m³ of dredged material from Sligo Harbour onto the former
landfill site at Finisklin is therefore considered to be unfeasible for the following reasons:
x
The lack of an engineered cap means that the landfill gas is currently venting through the
capping layer in a diffuse manner, thus reducing its potential to migrate to the
surrounding commercial and residential premises. Placement of c. 250,000m³ of material
on top of the former landfill will pose a barrier to the gas, thus preventing it from venting
and greatly increasing the risk of dangerous levels of gas migrating laterally to the areas
surrounding the landfill. This would pose an unacceptable safety risk and it is unlikely the
risk would be able to be mitigated without significant additional gas venting works.
x
Placing the dredged sediment, which will be wet material, on top of the landfill will both
compress the material within the landfill and increase the amount of water passing
through the landfill contents. This poses a risk of leaching contaminants from previously
undisturbed portions of the landfill which could drain onto the foreshore or into the
underlying water table and cause an adverse impact on the neighbouring SAC and SPA
designated foreshore.
x
There is no current requirement for any additional capping material on the former landfill,
and if there were, the dredged material does not possess the necessary physical
properties of normal landfill capping material. Therefore, if the dredged material were to
be placed on the site, it would have to be placed there as a “waste material”. Disposing
of “waste” requires a waste licence from the EPA which would necessitate a separate EIA
and planning permission. In order for this scenario to be facilitated, the former landfill
would effectively have to be re-licensed as a landfill. Such permission is very unlikely to
be acquired due to the environmental and safety risks outlined above. In addition, as
described above in the general landfill option, the disposal of waste on land will attract
landfill tax which renders this option highly uneconomical.
x
The site of the former landfill, once it becomes available for development, will be a
valuable commercial site, particularly since it has excellent infrastructural connections
arising from electricity network, fresh water, drainage and high speed
telecommunications upgrades constructed in support of the new waste water treatment
works in the adjacent site. The dredged material would not have the structural properties
to provide a stable foundation for any future development and would require piling and
the significant increase in ground level would also pose a significant negative impact on
the site’s potential for development.
1-39
Introduction
Whilst the use of the former Finisklin landfill site initially appeared to be an option for the
disposal of the dredged sediments, this option is unable to be progressed due to the
environmental and safety reasons outlined above.
1.5.3.4 Incineration
There are no suitable incineration facilities in Ireland capable of accepting the proposed type
or quantity of dredge spoil. The dredge spoil would therefore need to be transported to
mainland Europe.
This option can therefore be ruled out due to prohibitive cost.
1.5.3.5 Reclamation within Sligo Harbour
Reclamation of the foreshore has been the traditional method for disposal of dredged spoil
arising from maintenance dredging in Sligo Harbour. The area of foreshore reclaimed from
this activity has been recently used to construct Sligo city’s new Waste Water Treatment
Plant (WWTP) and consequently there is no further space available within this area to
dispose of further material.
The examined option would be to reclaim a further part of Sligo Bay (3.17 hectares), within
an area known as Cummeen Strand. A suitably sized semi-enclosed location lies
immediately west of the previously reclaimed site of the new WWTP (Figure 1.5).
Figure 1.5
Suggested Reclamation Area
Aerial photograph ESRI/Bing Maps © Microsoft Corporation 2012
1-40
Introduction
Cummeen Strand holds a number of nature conservation designations including SAC, SPA,
Ramsar and pNHA. It is therefore an important site of high conservation value and includes
a number of habitats and species listed on Annex I and II of the EU Habitats Directive.
The option of reclamation does not present an adequate long term solution for the disposal of
dredged sediments from Sligo Harbour. Although the amount of sediment to be removed
would keep the channel operational for several years, maintenance dredging would still be
required and the reclamation area would be entirely filled by the 250,000m³, thus requiring a
new means of disposal to be identified for any future works.
Under the Habitats Directive, a plan or project may not proceed unless it is demonstrated to
have no significant impact on the integrity of a Natura 2000 site. Reclaiming 3.17ha of
intertidal sandflats and mudflats from the SAC/SPA area would pose a significant and
permanent negative impact to the footprint, altering it from its status as an Annex I habitat.
Under these circumstances, the project would not be given consent to proceed unless no
alternative was found to be available and imperative reasons of overriding public interest
could be demonstrated. In addition, an equivalent area of compensatory habitat would also
have to be designated in its place. Since virtually all of Sligo Harbour and the surrounding
coastline has already been designated as a SAC or SPA, the opportunities are very limited in
providing compensatory habitat for a direct loss of habitat at the proposed reclamation site in
Cummeen.
As there are alternatives which exist which do not require the loss of SAC and SPA habitat,
this option must therefore be ruled out on conservation grounds.
1.5.3.6 Water Injection/Plough Dredging
Water injection is relatively new method of dredging which operates by injecting water into
certain fine-grained sea bed materials, reducing their density to the point where they act as a
fluid and flow over the bed through the action of gravity to lower levels. Although the
sediments are not raised from the surface of the water, this technique still requires a
dumping at sea licence under the Dumping at Sea Act:
“dumping” means—
(a) any deliberate disposal in the maritime area (including side-cast dredging,
plough dredging, water injection dredging and other such dredging techniques) of
a substance or material from or in conjunction with a vessel or aircraft or offshore
installation.
This type of dredging can create significant amounts of turbidity at the bottom of the water
column which would have the potential to cause adverse impacts including smothering of the
intertidal and benthic species within the SAC and consequently the SPA species which would
feed on these.
1-41
Introduction
Water injection dredging is mainly used to remove small amounts of sediment quantities
(less than 5,000m³) although in certain areas it has been used for quantities up to 25,000m³
(Sullivan, 2000). Typically it tends to be used most often to move sediments in difficult to
access areas (such as beneath marina finger berths) into the path of a conventional dredger.
The major limitation of water injection dredging techniques is a loss in effectiveness with
increasing quantities of material removed. It would be unfeasible to attempt to relocate
250,000m³ of sediments from the navigation channel at Sligo Harbour using this method as
the amount of turbidity generated would be unacceptable. Furthermore, as the harbour is an
enclosed area, the displaced sediments would merely resettle elsewhere in the harbour and
would most likely be returned to the navigation channel within a short time scale.
Plough dredging is a more basic method of this type of dredging, where sediments are
physically pushed aside from the area to be dredged. This type of dredging is suitable for
clearing small areas, however as the sediment is not actually removed from the system it is
often a very temporary measure, particularly where the grain size is fine, as the sediment can
rapidly migrate back to the dredge pocket. Plough dredging would not be a suitable means
of removing the 250,000m³ of sediment in Sligo Harbour, particularly as the training walls
would provide a physical barrier constraining the area in which the sediment could be
redistributed.
1.5.3.7 Dumping at Sea
The dumping at sea option would require transporting the dredged material directly from the
dredging area to an agreed offshore location where it would be discharged from the vessel
(e.g. by bottom-opening hopper) for disposal.
The OSPAR Convention 1992 (The Convention for the Protection of the Marine Environment
of the North-East Atlantic) regulates international cooperation on environmental protection in
the North-East Atlantic. It updates the 1972 Oslo Convention on dumping waste at sea and
the 1974 Paris Convention on land-based sources of marine pollution.
In Ireland, dumping at sea is only permitted at an authorised dump site and a dumping at sea
licence must be sought by the applicant. There are currently no operational dump sites
within Donegal Bay (a dumpsite was formerly licensed for the disposal of dredged material
from the upgrading of Killybegs Fishery Harbour in 2003; however this dump site was
subsequently closed upon completion of the scheme).
Therefore, as part of this scheme, a suitable location for a new dump site must be identified.
The process of identifying a new dump site has been described in more detail in Section 2.2
of Chapter 2, “Consultations”.
The Foreshore and Dumping at Sea (Amendment) Act 2009 amends the Dumping at Sea
Acts 1996 to 2006. This has transferred responsibility for functions relating to dumping at
sea from the Minister for Agriculture, Fisheries and Food to the Environmental Protection
Agency (EPA).
1-42
Introduction
In accordance with Section 5 (2) of the Dumping at Sea Acts 1996-2009 (as amended) the
dumping of substances or material at sea is only acceptable when the Agency is satisfied
that there is no suitable alternative means of disposal of the material concerned. The
applicant must also demonstrate that all necessary steps have been taken to minimise the
quantity of material to be dumped or render the material less harmful for dumping at sea.
The feasibility of the other various means of disposal or reuse of the dredged sediments has
been examined in detail in the sections above. Owing to the environmental constraints within
Sligo Harbour and the physical composition of the sediments, dumping at sea is considered
to be the only viable disposal mechanism available for the disposal of the dredged material.
Sediment quality analysis has been undertaken on the sediments to be dredged, under the
supervision of the Marine Institute. The results of the analysis are described in more detail in
Chapter 10 “Geology and Soils”. The results demonstrate that the sediments are clean in
terms of the guidance valies set by the Marine Institute (Cronin et al, 2006), and do not pose
any known environmental threat, should they be disposed of at sea.
The predicted impacts of the dumping the dredged sediments at sea in terms of marine
ecology, fisheries and archaeology are described in more detail in Chapter 6, Chapter 7 and
Chapter 12 respectively. These impacts are considered to be insignificant and the disposal
of the dredged material at an offshore dump site, subject to licensing, is considered to be the
most appropriate means of disposing of the dredged material from the capital and
maintenance dredging of Sligo Harbour.
1-43
1.6
Introduction
THE CONSENTING PROCESS
The proposed dredging is beneath the thresholds for EIS as set out in Schedule 5 of the
Planning and Development Regulations 2001-2011. However, where a sub-threshold
development is proposed within a conservation area such as a European site (e.g Special
Protection Area or Special Area of Conservation), a local authority may request the Board to
determine the question of whether a development would be likely to have significant effects
on the environment, in which case an EIS must be prepared.
A request for a direction from An Bord Pleanàla as to whether an environmental impact
statement is required for the proposed dredging scheme was issued by RPS on behalf of
Sligo County Council on 2nd August 2011. On 30 May 2012 the Board issued their decision
that an EIS would not be required.
As the project has been evaluated as not requiring an EIS, it does not fall under the remit of
any of the Planning categories in Part XV of the Planning and Development Act (2000) (as
amended).
Instead, however, the scheme will require consent through the Foreshore Licensing process.
In addition, as there are no currently licensed dump sites in operation in Donegal Bay,
permission must be sought for the creation and use of a new dumping at sea disposal area.
1.6.1
Required Permissions
1.6.1.1 Foreshore Licensing
The key legislation relating to offshore marine developments are the Foreshore Acts 1933 –
2009. This relates to a collective series of Acts, comprising the following:
x The Foreshore Act 1933
x The Foreshore (Environmental Impact Assessment) Regulations, 1990
x The Foreshore (Amendment Act) 1992
x Section 5 of the Fisheries and Foreshore (Amendment) Act 1998
x Fisheries (Amendment) Act 2003 (Part 5)
x Maritime Safety Act 2005 No. 11 (Part 6)
x Foreshore and Dumping at Sea (Amendment) Act 2009
Before the commencement of any works or activity on State-owned foreshore, a lease or
license must be obtained from the relevant Minister. This relates to the carrying out of works
or placing of structures or materials on, or for the occupation of or removal of material from
State-owned foreshore which represents the greater part of the foreshore. Developments on
privately owned foreshore also require the prior permission of the Minister under the
Foreshore Acts. All the foreshore of Ireland is presumed state-owned unless valid alternative
title is provided.
1-44
Introduction
The foreshore is the seabed and shore below the line of high water of ordinary or medium
tides and extends outwards to the limit of 12 nautical miles (or 22.224 km).
Applications for foreshore licences or leases are separate from terrestrial planning
applications; are granted subject to the payment of fees; and the relevant Minister has
absolute discretion to accept or reject a proposal to use state-owned foreshore.
x
A Foreshore Lease is generally required for the long term construction and operation
of an intended project that requires exclusive occupation of the foreshore (e.g., piers,
marinas, bridges, roads, and offshore wind farms). Such structures would generally
preclude the use of that part of the foreshore for other purposes;
x
A Foreshore License is generally required to investigate the suitability of a site for an
intended project or for other works (e.g., laying of submarine pipelines and cables)
and purposes (e.g., aquaculture) i.e., for development that does not require exclusive
occupation of the foreshore. Such activities/development would not generally
preclude the use of that part of the foreshore for other purposes.
A foreshore licence application will therefore be made to the Department of Environment,
Community and Local Government (formerly known as the Department of Environment,
Heritage and Local Government prior to May 2011)
1.6.1.2 Dumping at Sea Licensing
Prior to 15th February 2010, dumping at sea was regulated under the Dumping at Sea Acts,
1996 and 2006. The Coastal Zone Management Division (CZMD) of the Department of
Agriculture, Fisheries and Food was charged with implementing the provisions of these Acts
i.e., permitting of dumping at sea operations. The Dumping at Sea (Amendment) Act, 2009,
transferred the responsibilities for controlling dumping at sea from the CZMD to the
Environmental Protection Agency (EPA). All permit applications are now processed by the
Environmental Licensing Programme of the Agency.
The purpose of a Dumping at Sea permit is to regulate the dumping of material at sea. The
Dumping at Sea Acts, 1996 to 2009, provide for the implementation of the requirements of
international Conventions regulating the disposal of dredged materials at sea: the London
Convention of 1972 (including the 1996 Protocol) and the OSPAR Convention for the
Protection of the Marine Environment of the North-East Atlantic), adopted in 1992. The
aforementioned Acts prohibit the dumping at sea of a substance or material unless permitted
by the Agency.
Disposing of a substance or material at sea without a permit, or contravening the conditions
of a Dumping at Sea permit, are offences under the Dumping at Sea Acts, 1996 to 2009.
Offenders are liable upon conviction to a fine or imprisonment or both.
1-45
Introduction
Dumping at Sea Permits are only granted for the disposal of dredge material from ports,
harbours and marinas in the absence of suitable alternative reuse and disposal methods.
A Dumping at Sea Licence application for a new dump site will therefore be made to the
Environmental Protection Agency
1-46
2.0
Consultations
CONSULTATIONS
The consultation phase of the project timeline is of key importance, as it enables all
concerned and interested parties to voice their opinions on the development during the initial
stages of the project. This enables changes to be made during the design phase of the
development, incorporating comments and ideas from the consultation process.
Consultation meetings were held with the principal consultees such as the Department of
Agriculture, Fisheries and Food, the Department of Environment, Community and Local
Government (formerly the Department of Environment, Heritage and Local Government) and
the Environmental Protection Agency at the outset of the project. This consultation with
statutory bodies continued throughout the Environmental Appraisal and particularly when
potential issues were arising during the impact assessment phase. In addition, meetings
were also held with key non-statutory consultees including the Killybegs Fishermen’s
Organisation and the Sea Fisheries Protection Authority.
In November 2009, the Department of Agriculture, Fisheries and Food, then the authority
responsible for Foreshore Licensing, advised that a full Environmental Impact Assessment
was required for the proposed dredging and an Environmental Impact Statement (EIS) would
be necessary, therefore consultations and impact studies were undertaken on this basis.
This direction to prepare an EIS was subsequently over-ruled by An Board Pleanàla, who
overtook responsibility for Local Authority development on the Foreshore in 2010 and who
issued a determination that the project would not require an EIS to be prepared in May 2012.
Letters were sent out to all relevant stakeholders and consultees, informing them of the
extent of the dredging, the proposed dumpsite location and inviting their comments on the
scheme. The consultees who were contacted about the proposed development are listed
below in Table 2.1. A summary of the written responses received from those consultees is
provided in Appendix 2A. Copies of the written responses are included in Appendix 2C.
Table 2.1 Organisations/Agencies consulted as part of the Appraisal Process
Office of Climate, Licensing and Resource Use
Fáilte Ireland North West
Development Applications Unit
Federation of Irish Fishermen
Department of Communications, Energy and Natural
Resources
Foreshore Unit, Department of the Environment,
Heritage and Local Government
Department of Transport
Geological Survey of Ireland
Sligo County Council
Health and Safety Authority
An Taisce The National Trust for Ireland
Heritage Ireland
Aquaculture and Foreshore Management Division,
Department of Agriculture, Fisheries and Food
Iarnrod Eireann
Birdwatch Ireland
Irish Coast Guard
Blue Flag Beaches
Irish Federation of Sea Anglers (Connaught)
Bord Gais Eireann
Irish Whale and Dolphin Group
Bord Iascaigh Mhara
Marine Institute
Central Fisheries Board
Maritime Safety and Environment, Department of
2-1
Consultations
Transport
Coastwatch
National Monuments Section, Department of the
Environment, Heritage and Local Government
Coillte
National Parks and Wildlife Service
Commissioners of Irish Lights
National Roads Authority
Department of Education and Science
North Western Regional Fisheries Board
Department of Enterprise, Trade and Innovation
Northern Regional Fisheries Board
Department of Finance
Office of Environmental Assessment
Department of Health and Children
Office of Public Works
Donegal Bay Sea Angling Club
RNLI
Eircom
Sligo Harbour Commissioners
Tourism Development Policy Division, Department of
Tourism, Culture and Sport
Underwater Archaeology Unit, Department of the
Environment, Heritage and Local Government
Electricity Supply Board
Engineering Division, Department of Agriculture,
Fisheries and Food
Inland Fisheries Ireland
2.1
DUMPING AT SEA CONSULTATIONS
A feasibility study undertaken for the dredging scheme by RPS in 2010 (see also
“Consideration of Alternatives” (Chapter 1.5) of this Environmental Appraisal) concluded that
the only viable means of disposing of the waste material arising from the dredging project
was by dumping at sea at an offshore dump site.
An offshore dumpsite previously existed within Donegal Bay which was used for the disposal
of sediments arising from the upgrading of Killybegs Harbour in 2002. However, this
dumpsite is closed to new applications and it was necessary to choose a location for a new
dump site.
Consultation on a suitable dump site location was subsequently held with the Environmental
Protection Agency, the Sea Fisheries Protection Authority, the regional Fisheries Board, Bord
Iascaigh Mhara, the Department of Agriculture, Fisheries and Food and the Marine Institute.
Opinions were also sought from the Killybegs Fishermen’s Organisation (KFO) and the Irish
Fish Producer’s Organisation (IFPO).
Three potential dump site locations within Donegal Bay were presented to these consultees
(Figure 2.1).
The initial site proposed during initial scoping was located approximately 15 nautical miles
from the port, due west of Ballyconnell Point in approximately 50 metres water depth. This
site was advised as being unsuitable by BIM and the Sea Fisheries Protection Agency as
there are known spawning areas nearby and the site is also within the migration route for
salmon species.
2-2
Consultations
At a meeting with the Department of Agriculture, Fisheries and Food and representatives of
the KFO in February 2010, the KFO strongly objected to any dumping at sea activities taking
place within the confines of Donegal Bay and stated that any potential dump site should be
located west of a theoretical line marking the entrance to Donegal Bay, stretching between
Malin More Head and the Broadhaven Stags (Figure 2.1).
Figure 2.1
Dumpsite Consulted Sites
Extract from Admiralty Chart 2725 © Crown copyright UKHO. Not for Navigation Use
The second site proposed was located approximately 25 nautical miles from the port, due
north of Rathlee Head in approximately 60 metres water depth. This site was also
considered to be unsuitable by BIM and the KFO as it is within a highly productive fishing
area and the local tidal currents would potentially sweep the sediment east in to Donegal
Bay. The KFO expressed their support for the dredging project, however they reiterated their
objections to any dumping taking place inside the Malin More Head – Stags line and added
that the site should also be in excess of 100 metres water depth.
RPS subsequently undertook some preliminary tidal current modelling to locate a potential
dump site where residual tidal currents would not sweep any of the dumped sediments east.
The site finally chosen as the proposed dump site is west of the Malin More Head – Stags
line and is in water depths of 92-93 metres. Examination of the tidal current modelling of the
site shows that the residual tidal currents travel in a northerly direction and so would not
transport the dumped sediment back into Donegal Bay. The site is approximately 34 nautical
miles from the berths at Sligo Harbour. Published Admiralty charts have poor coverage of
this area of seabed, showing the area as “unsurveyed” and there is an inferred 100m contour
2-3
Consultations
5nm west of the proposed dump site. Accurate bathymetry information was therefore instead
obtained from the GSI/Marine Institute InfoMar project. At the proposed dump site location,
the seabed is relatively flat and the true 100m depth contour is some 30km west of the 90m
contour. This is beyond the viable range of a small dredger.
It should also be noted that the area around the 100 metre contour is shown in the Atlas of
Commercial Fisheries Around Ireland (Marine Institute, 2009) as being a much more heavily
fished area in terms of hours effort per square nautical mile, based on data recorded in the
VMS (Vessel Monitoring System) database.
Details of this revised dump site were issued to Bord Iascaigh Mhara (BIM), the Marine
Institute, the Killybegs Fishermen’s Organisation, the Irish Fish Producer’s Organisation, the
Geological Survey of Ireland, the North West Regional Fisheries Board and the Sea
Fisheries Protection Agency in June 2010 as well as being included within the EIA
consultation package sent to the consultees outlined in Table 2.1.
BIM responded that the site appeared to avoid the main fishing areas. The Marine Institute
responded that they could see no issues with this site, especially given that the material is
clean. No immediate response was received from the Regional Fisheries Board or the Sea
Fisheries Protection Agency.
GSI reviewed information provided by the Infomar project and from the confirmed that the
proposed dumping site is located west of an important moraine, approximately running NESW, which, along with the identified tidal currents, would act as a natural barrier to the redeposition of any dredged material towards Donegal Bay and Sligo Bay. GSI also confirmed
that no particularly important forms of life (e.g. cold water corals and others) were identified
in that area on the seabed during the Infomar survey. Backscatter information from the
survey indicated that the substrate is likely to be coarse sand and gravel, although the bed is
a mosaic of substrate types in this area. The nearest areas of uniformly sandy substrate
west of the moraine are 10-12 kilometres further from the port and beyond the range of the
dredger. East of the moraine ridge is a large sandy area which would have potentially been
suitable, but this area is a heavily fished and would not be acceptable to fishermen as the
sediments would be confined inside Donegal Bay.
The KFO and IFPO stated their continued concerns regarding the choice of dumping at sea
as being the preferred disposal method. Although the site is west of the theoretical Malin
More Head – Stags line both groups expressed fears that the plume of dumped material will
spread widely into Donegal Bay and may affect juvenile and spawning grounds. Both groups
are opposed to any dumping at sea proposal and feel that alternative disposal methods on
land should have been examined in more detail. IFPO also indicated that there are pot
fishermen fishing within the proposed site and that the presence of any heavy metals in the
dredged spoil could contaminate the crabs or lobsters and subsequently result in the catch
being excluded from the market.
RPS have taken the responses from the various consultees on board during the site
selection process. A further assessment of alternative disposal sites on land or involving
2-4
Consultations
reclamation of the foreshore was undertaken (See Section 1.5 of Chapter !, Introduction) to
ensure that dumping at sea was being undertaken as a last resort. However, no more
suitable locations were able to be identified for the disposal of the material.
It will be clearly demonstrated within this Environmental Appraisal that the dredged spoil is
free of harmful contaminants (Chapter 14 Sediment and Water Quality) and that there will be
no significant impacts to marine flora and fauna arising from disposing of this material
offshore (Chapter 6 Marine Intertidal and Subtidal Flora and Fauna). Detailed modelling of
the dispersal plume is shown in Chapter 11, Coastal Processes.
2.2
PUBLIC CONSULTATION
Public consultation is an important part of the EIA process, as it allows stakeholders outside
the statutory and non-statutory consultee bodies to have an opportunity to become involved
in the EIA and offer their views on the proposed scheme.
A public consultation event was held on 9th February 2011. The event involved open
afternoon/evening sessions in the Sligo County Council offices at Market Yard in Sligo.
The proposal was exhibited in a display, showing the dredging and proposed dumpsite
locations as well as summarising the key issues being examined in the Environmental
Appraisal (Appendix 2B). Present to answer questions were Gary Salter of Sligo County
Council, Dr Alan Barr and Sophie Gilloway of RPS and Dr Paul Johnson, independent
fisheries consultant.
The public consultation sessions were advertised in the local newspaper and a notice was
placed on the Sligo County Council website. Additionally, local stakeholders who had been
identified as potentially having an interest in the scheme, such as shellfish cultivators, local
conservation groups, boat charter operators and fishermen, were also issued direct
invitations.
The afternoon session was held between 2pm and 4pm. This was well attended by in
excess of 25 visitors, including the main local shellfish cultivators, Inland Fisheries Ireland,
Co. Sligo based pot fishermen, Bord Iascaigh Mhara, local boat charter companies and other
harbour users.
Key issues raised during this session were:
x
Impact of suspension of sediments during dredging activities on salmonid species
travelling through Sligo Harbour to Lough Gill. Visitors seemed to be reasonably
satisfied that the methodology and mitigation measures would reduce this impact to
insignificant levels.
x
Impact of suspension of sediments during dredging activities on shellfish cultivation
areas. Cultivators seemed to be reasonably satisfied that the methodology and
mitigation measures would reduce this impact to insignificant levels.
2-5
x
Consultations
Impact of disposing of dredged sediments at offshore dumpsite on crab, lobster and
demersal fisheries. Fishermen are concerned that if crustaceans ingest or inhale
suspended sediments the value of their catch will be reduced as contamination with
sand or grit will lower the prices paid per crab. Crabs prefer the sandy substrate,
lobsters prefer rocky substrate and all these habitats are present at the dumpsite. The
fishermen were not satisfied that mitigation measures would prevent impacts.
It was recognised by the fishermen that the dumpsite had been moved outside the main
pelagic fishing and spawning areas in Donegal Bay, which has helped to reduce some
concerns about the impact of dumping at sea. However, some concern was raised that
although outside Donegal Bay, the proposed dumpsite area is regarded as a popular and
productive area for crab and lobster potting, as well as other species such as dogfish.
Further consultation was recommended with the fishermen who fish this area.
The evening session was held between 5:30pm and 7:30pm. This session was again well
attended with a large group of pot fishermen from Sligo, Mayo and Donegal present. Also
present was a local councillor.
The pot fishermen held very strong concerns about the dumping of the dredged spoil
offshore. Their key concerns were:
x
The dredged material may potentially contain substances harmful to crustaceans, as
until 2009 the city’s sewage was discharged without any treatment into the river channel.
Although the sediments have been tested under the supervision of the Marine Institute
and found to be clean, the fishermen continue to have concerns.
x
A large area in the outer reaches of Donegal Bay west of 9°W was highlighted by the
fishermen as being a very productive area for both crab and lobster fishing and probably
spawning (Figure 2.2). The fishermen estimate that over 40,000 pots are laid around
this area. The fishermen are concerned that the tidal and wave driven currents in the
area will disperse the dumped sediments over a very wide area, thus causing a
widespread impact footprint. Fishermen estimate current speeds of 2.5 knots (1.3 m/s)
at the dump site during spring tides.
x
The fishermen also hold concerns that if this area becomes a licensed dumpsite, other
ports will make applications to dispose of spoil here and the issues arising from dumping
at sea will continue on a longer term basis.
x
The fishermen concluded that they would oppose any dumping at sea application and
that the council should re-examine all alternative methods of disposing of the sediments
on land. The fishermen are not satisfied that environmental designations within the
harbour should mean that this area is protected from having the material disposed of
there, when in their opinion the dump site area is just as important to them.
At the time of the public consultation, no information on the fate of the dredged material
following its disposed was available as model studies had not been completed. It was
2-6
Consultations
agreed that once the dump site plume modelling and benthic impact hypothesis had been
completed (in the absence of an alternative land-based dump site being located), RPS would
re-engage with the fishermen to discuss the potential impacts to the pot fisheries.
Figure 2.2
Pot Fishing area as indicated in Public Consultations
2.3
ADDITIONAL OFFSHORE FISHERIES CONSULTATION
Following the public information day in February 2011, further consultation was held with
representatives of the crab fishing industry. These included the local BIM Fisheries Officer,
Declan Nee and a local crab fisherman who attended a meeting with the project fisheries
representative on 17th February 2011. Further consultation was undertaken by telephone
with the following:
x Oliver Tully – Marine Institute
x Owen Doyle - local BIM Fisheries Officer – Donegal/Sligo
x Grainne O’Brien – BIM Environmental Officer
x John Dennis – BIM
x Ben Dallaghan – BIM
x Aisling Donegan – IFI Ballina – Environmental Officer
x Lesley McCaffrey – SFPA Killybegs
x Anthony Keohane – SFPA Clonakilty
x Daryl Ewing – charter boat operator
x Kevin Barber – Sea Angling
2-7
Consultations
Ongoing consultation and liaison with the commercial pot fishermen within the region is
expected to continue throughout the duration of the proposed project.
2.4
LOCAL AQUACULTURE
The main local aquaculture producers met with the project’s fisheries representative on 17th
February 2011 to discuss the potential issues relating to their commercial interests. These
were:
x Noel Carter – Coney Island Shellfish Ltd
x Charles Kelly – Atlantic clams Ireland Ltd
x Paul Leydon – Armada Shellfish Co
2.5
RESPONSE TO ISSUES RAISED DURING CONSULTATION
Following the comments made during the public consultations, RPS undertook a thorough reexamination of the alternative disposal methods, including more detailed research into the
options at Finisklin landfill and the reclamation of an area of foreshore. These are described
in Chapter 1.3 “Consideration of Alternatives”.
RPS also re-engaged with the Marine Institute to verify the potential for the sediment to
contain elements harmful to crustaceans. The Marine Institute have confirmed that the
chemical testing of the sediments indicates that all concentrations of potential contaminants
are below the lower guidance level threshold. This threshold is set at a level below which no
ecological risk is associated. Full recognition has been taken of the history of the sediments
during the testing regime, i.e. that prior to 2009 untreated sewage was being discharged into
the main channel and that the site is working port.
Current metering and drogue tracking has taken place at the dump site during both spring
and neap tides. Video footage and grab samples have also been taken. This information
has been be used to model the dispersion footprint of the dumped sediments and quantify
how widespread the impacted area is likely to be and whether the impacts are likely to be
significant, discussed in detail in Chapter 6 “Intertidal and Subtidal Flora and Fauna”.
2.6
CONCLUSIONS
The issues raised during both the public consultation and the stakeholder consultation period
have been addressed and, where possible, mitigated for to reduce the environmental impact
of the development. It will be seen that the impact to the environment from the dredging , in
particular to the designated SAC and SPA areas at Cummeen Strand in addition to the EU.
Shellfish Water have been addressed in full in the Environmental Appraisal Report (Chapters
5, 6, 7 and 11) and Natura Impact Statement (Volume 3).
The decision to dispose of the dredged material at an offshore dump site has been taken
after careful and detailed consideration of all other potential options. Detailed studies have
taken place to quantify the risk of adverse ecological impacts occurring at the dump site and
2-8
Consultations
these studies have concluded that the disposal of c. 250,000m³ of dredged sediments will
pose no significant impacts to marine benthic and fish species, including crustaceans.
The various submissions and comments made in relation to the proposed dredging Sligo
Harbour have been fully considered by the consultants in the preparation of the
Environmental Appraisal and in the design of the scheme. Every effort has been made to
address all concerns raised and, where possible, mitigation measures have been proposed
to minimise the environmental impact of the proposed development.
2-9
Consultations
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2-10
Site Description
3.0
SITE DESCRIPTION
3.1
INTRODUCTION
Sligo Harbour is a large, shallow bay stretching from Sligo city westwards to Coney Island, in
County Sligo on the west coast of Ireland. It is one of three enclosed estuaries which make
up Sligo Bay, with Drumcliff Bay to its north and Ballysadare Bay to its south. The
Garavogue River (sometimes written as Garvoge, Garavoge or Garvogue) flows into the
harbour, forming a permanent channel. Sligo Bay is part of Donegal Bay which opens into
the Atlantic Ocean.
Sligo Harbour and Sligo city are surrounded by a mountainous skyline, with the ridges of
Slieve Daeane and Killery Mountain to the south-east, Cope’s and Keelogyboy Mountains to
the northeast, the highly-distinctive Knocknaree to the west and Benbulbin to the north.
© Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council
Figure 3.1
Site Location (Regional Context)
The northern boundary of Sligo Harbour is the peninsula of Rosses Point. Rosses Point,
approximately 6km in length, divides Sligo Bay from Drumcliff Bay. Rosses Point hosts the
popular County Sligo Golf Course and has two west-facing fine sandy beaches, stretching for
more than 1.5km. These beaches, popular because of their safety and proximity to the city
of Sligo, hold a Blue Flag award. The largest settlement on Rosses Point peninsula, Rosses
Point village, lies on its southern shore at the entrance to Sligo Harbour. At the last census
3-1
Site Description
(CSO, 2012a) the Rosses Point peninsula had a population of 1,517. Immediately south of
Deadman’s Point and south west of Rosses Point village, the “Metal Man” navigation beacon
marks the entrance to the navigation channel into Sligo harbour.
To the south of Sligo Harbour lies the Coolera peninsula (sometimes called Strandhill
peninsula) which separates Sligo Harbour from Ballysadare Bay. The main settlement on
the Coolera Peninsula is Strandhill (CSO 2012a population 1,210), which is the location of
Sligo’s regional airport and is a popular surfing beach. On the north western corner of the
Coolera peninsula is Killaspugbrone townland, which holds an ecclesiastical complex
comprising a church, enclosure, graveyard and shrine, parts of which date from the 11th –
12th century.
Sligo city has developed at the mouth of the Garavogue River, which is a short river (4.3 km
long) connecting Lough Gill with the sea. The Garavogue, despite its short length, is popular
with canoeists and is also reputed for its excellent fishing. Lough Gill, which is nearly six and
a half miles long and two and a half miles wide, is also a popular fishing and tourist area and
was the subject of several poems by W.B. Yeats such as “The Lake Isle of Innisfree”.
Sligo's Irish name Sligeach - meaning shelly place - allegedly originates in the abundance of
shellfish found in the river and its estuary, and from the extensive 'shell middens' or Stone
Age food preparation areas in the vicinity. Although Sligo is not an especially large city in the
national context, with a population of 19,452, it is the largest town in the province of
Connaught (CSO, 2012b), making it important in a regional context. Due to its status as a
regional growth centre and gateway to the North-West, its daily population expands to over
42,000 (Sligo Chamber of Commerce, 2011).
Sligo is an historic, cultural, commercial, industrial, retail and service centre of regional
importance. Served by a regional airport and established rail, port and road links, Sligo city
exerts significant influence on its immediate hinterland. This hinterland, comprising the
county of Sligo and beyond is essentially rural in character. The county is characterised by
relatively small towns and villages providing local commercial, retail and support services
with sparsely populated environs depending largely on agriculture and tourism related
business.
At the entrance to Sligo Harbour lies Coney Island. The island is accessed by a causeway
across the beach by car or foot when the tides are low. The island has few permanent
residents but is a popular tourist destination, especially in the summer months. The island’s
name derives from the large rabbit population it formerly hosted.
Extending west from Coney Island is a training wall which connects the island with Black
Rock and the Blackrock lighthouse. This training wall is named the Cluckhorn and was
constructed from rock armour between 1908 and 1912. The aim of the training wall was to
remedy the navigational difficulties in accessing Sligo Harbour, by enhancing the tidal flows
through the entrance channel and thus keeping the entrance clear of sediments.
3-2
Site Description
Whilst this training wall has been largely effective in maintaining navigable depths into Sligo
Harbour, passage through the Bungar Bank, which is highly mobile, can be difficult and
pilotage into Sligo Harbour is compulsory for commercial vessels.
3.2
SITE CONTEXT AND EXISTING LAND USE
3.2.1
Sligo Harbour Development
Under the 1996 Harbour Act, the government proposed the transfer of control of a number of
regional ports and harbours to local authorities, Sligo Port was one such harbour where a
transfer to Sligo County Council has taken place by Ministerial Order. A grant of €1.85m was
obtained from the Department of Transport - Marine Section to carry out essential works.
Approximately 90 acres of land under the control of the Harbour Commissioners, most of
which had been reclaimed from the sea since the 19th century, including the site of the former
landfill, were transferred to Sligo County Council (SBC/SCC, 2011).
Finisklin Landfil
Timber Jetty
Sligo WWTP
Barytes Jetty
Deepwater Jetty
Cartron Marsh
Plate 3.1 Sligo Docklands
Photo: Sligo County Council
Plate 3.1 shows the majority of the docklands area. The roughly square bunded area
formerly used for the disposal of dredged sediment and which now hosts the city’s new main
drainage waste water treatment works is visible on the lower right of the image. Adjacent to
this can be seen the Barytes and Deepwater jetties which were refurbished with part of the
3-3
Site Description
grant awarded by the Department of Transport. Also included within this programme of
works was the refurbishment of the training wall.
South west of the waste water treatment works is the site of a former landfill at Finisklin. The
formerly filled area comprises approximately 13ha (Malone O’Regan, 2011). The landfill was
closed in 1994, however it continues to produce methane gas as a byproduct of the
breakdown of organic products contained within it.
Further south east along the navigation channel, within the inner part of Sligo Docklands is
the new access and safety facilities at Lynn’s Place - the Timber Jetty. This new facility,
opened in 2008, allows leisure vessels to tie alongside the pontoons at any tide level and
visitors to access the quay top via the articulating ramp.
Plate 3.2 and 3.3.
Timber Jetty
North east of the Deepwater and Barytes Jetties is a lagoon area, enclosed between Cartron
Point and Standalone Point, known as Cartron Marsh. This site forms a highly important
area for birdlife in Sligo Harbour and is included within the SPA and SAC designations.
3.3
NATURE CONSERVATION DESIGNATIONS
Sligo Harbour supports a diversity of natural and semi-natural habitats and a wide range of
flora and fauna. There are four environmentally designated sites within the dredging area:
x
x
x
x
Cummeen Strand/Drumcliff Bay Special Area of Conservation (SAC) (Figure 3.2)
Cummeen Strand Special Protection Area (SPA) (Figure 3.3)
Cummeen Strand/Drumcliff Bay proposed Natural Heritage Area (pNHA) (Figure 3.4)
Cummeen Strand Ramsar wetland (Figure 3.4)
A brief summary of the designations surrounding the proposed dredging area is given below.
More detailed examination on how the proposed dredging will affect these designated areas
will be given in Chapter 5 “Birds” and Chapter 6 “Intertidal and Subtidal Flora and Fauna”
3.3.1 Natura 2000
Sites holding the SAC (Special Area of Conservation) and SPA (Special Protection Area)
designations are known as Natura 2000 sites. The Birds and Habitats Directives set out
3-4
Site Description
various procedures and obligations in relation to nature conservation management in
Member States in general, and of the Natura 2000 sites and their habitats and species in
particular. A key protection mechanism is the requirement to consider the possible nature
conservation implications of any plan or project on the Natura 2000 site network, before any
decision is made to allow that plan or project to proceed. Not only is every new plan or
project captured by this requirement but each plan or project, when being considered for
approval at any stage, must take into consideration the possible effects it may have in
combination with other plans and projects when going through the process known as
“Appropriate Assessment”.
The Habitats Directive states: “Any plan or project not directly connected with or necessary to
the management of the site but likely to have a significant effect thereon, either individually
or in combination with other plans or projects, shall be subject to appropriate assessment of
its implications for the site in view of the site’s conservation objectives. In the light of the
conclusions of the assessment of the implications for the site and subject to the provisions of
paragraph 4, the competent national authorities shall agree to the plan or project only after
having ascertained that it will not adversely affect the integrity of the site concerned and, if
appropriate, after having obtained the opinion of the general public.”
3.3.1.1 Special Areas of Conservation
Special Areas of Conservation (SAC) are among the most important areas of wildlife habitat
in Ireland and throughout the European Union. The legal basis on which SACs are selected
and designated is the EU Habitats Directive, transposed into Irish law in the European Union
(Natural Habitats) Regulations, 1997 as amended in 1998 and 2005. SACs are selected for
the conservation of Annex I habitats (including priority types, which are in danger of
disappearance) and Annex II species (other than birds). Protected Irish habitats include
raised bogs, blanket bogs, turloughs (seasonal lakes in limestone areas), sand dunes,
machair (flat sandy plains on the north and west coasts), heaths, lakes, rivers, woodlands,
estuaries and sea inlets.
The aim of the Habitats Directive is to ensure the protection of biodiversity through the
conservation of natural habitats of wild flora and fauna and consequently 26 Irish species (6
mammals, 8 fish, 7 invertebrates, and 5 plants) which must be afforded protection are also
named in Annex II.
Other species are listed for protection measures on Annex IV and V, and some species
(such as the otter) are included on more than one annex. The annexed habitats and species
for which each site is selected correspond to the qualifying interests of the sites; from these
the conservation objectives of the site are derived. The Directive is binding on the Member
States and its agencies and the National Parks and Wildlife Service of the Department of
Arts, Heritage and the Gaeltacht is the statutory agency responsible for the selection and
designation of SACs.
Dredging works may have impacts on the intertidal and subtidal habitats and species which
use them for breeding, food and shelter.
3-5
Site Description
A summary of the features of the Cummeen Strand/Drumcliff Bay SAC is given below in
Table 3.1
Table 3.1
Cummeen Strand/Drumcliff Bay SAC Summary
Name
Cummeen
Code
Strand/Drumcliff
SAC
Bay
000627
Summary Description
This large coastal site extends from Cullamore in the northwest to Killaspug in the south-west, and from Sligo town in
the south-east to Drumcliff village in the northeast.
It encompasses two large, shallow bays (Drumcliff Bay and
Sligo Harbour), Ardboline and Horse Islands, sand dunes
and sand hills at Rosses Point, Killaspug, Yellow Strand and
Coney Island, grassland at Ballintemple and Ballygilgan
(Lissadell) and a variety of other habitats (woodland, salt
marsh, sandy beaches, boulder beaches, shingle, fen,
freshwater marshes, rocky sea cliffs, lakes). The site is
largely underlain by Carboniferous limestone, but acidic
rocks are also found on the Rosses Point peninsula. The
dominant habitats on the site are estuaries and intertidal
sand and mud flats.
Qualifying Habitats
x
Estuaries
x
Mudflats and sandflats not covered by seawater at low
tide
x
Shifting dunes along the shoreline with Ammophila
arenaria (white dunes)
x
Fixed coastal dunes with herbaceous vegetation (grey
dunes)
x
Embryonic shifting dunes
x
Petrifying springs with tufa formation (Cratoneurion)
Juniperus communis formations on heaths or calcareous
grasslands
Qualifying Species
Phoca vitulina (harbour seal)
Vertigo angustior (narrow mouthed whorl snail
3-6
Site Description
© Ordnance Survey Ireland. All rights reserved.
Licence number 2010/20 CCMA/ Sligo County
Council
Figure 3.2
SAC Designated Areas
3.3.1.2 Special Protection Areas
Special Protection Areas (SPAs) are designated because they are important habitats for
birds. The legal basis for the SPA is the European Birds Directive (79/409/EEC) which was
transposed into Irish Law mainly by the Wildlife Act and the Wildlife (Amendment) Act, 2000
and the European Communities (Conservation of Wild Birds) Regulations, 1985.
The EU Birds Directive (79/409/EEC) requires designation of SPAs for:
x
x
x
x
Annex I listed rare and vulnerable species.
Regularly occurring migratory species, such as ducks, geese and waders.
Wetlands, especially those of international importance, which attract large numbers of
migratory birds each year. (Internationally important means that 1% of the population of
a species uses the site, or more than 20,000 birds regularly use the site.)
Annex I birds are those that require special conservation measures because they are rare, in
danger of extinction, or vulnerable to habitat changes in the EU. Ireland supports populations
of 33 Annex I bird species. The SPA network includes important seabird colonies, wintering
waterfowl sites, and sites supporting rare species (e.g. the corncrake).
A judgment delivered by the European Court of Justice in December 2007 (C-418/04) found
Ireland to have been in breach of the requirements of the Birds and Habitats Directives in a
number of areas. This included a finding that the designation of Ireland’s original suite of
Special Protection Areas (SPAs) was inadequate and did not meet the full requirements of
3-7
Site Description
the Directives. The Court also found that some of Ireland’s SPAs were not sufficiently
extensive to include all important habitat for the birds in question.
A summary of the features of the SPAs at Cummeen Strand and Drumcliff Bay is given below
in table 3.2
Table 3.2
Sligo Harbour and Drumcliff Bay SPA Summary
Name
Code
Cummeen Strand SPA
004035
Summary Description
Cummeen Strand is a large shallow bay stretching from
Sligo town westwards to Coney Island. The Garavogue
River flows into the bay and forms a permanent channel.
At low tide, extensive sand and mud flats are exposed.
These support a diverse macro-invertebrate fauna which
provide the main food supply for the wintering waterfowl.
Areas of salt marsh fringe the bay in places and provide
roosting sites for birds during the high tide periods. There
are sand dunes at Killaspug Point and Coney Island, with a
shingle spit at Standalone Point near Sligo town.
Qualifying Species
Brent Goose, Oystercatcher, Redshank, Golden Plover, Bartailed Godwit and Whooper Swan
Drumcliff Bay SPA
004013
Both Drumcliff Bay and Cummeen Strand are important for
the large numbers of waterfowl which use them in
autumn/winter, including Ringed Plover, Redshank, Lapwing,
Knot, Bar-tailed Godwit, Oystercatcher, Curlew, Golden
Plover, Dunlin, Turnstone, Brent Goose, Grey Heron, Teal,
Wigeon, Mallard, Shelduck and Redbreasted Merganser.
The fields at Lissadell and Ballintemple support one of the
largest populations of Barnacle Goose in the country (c2000
in winters of 1995/96 and 1996/97). The important feeding
site for Barnacle Geese at Lissadell is a Statutory Nature
Reserve
Qualifying Species
Barnacle Goose, Chough, Golden Plover and Bar-tailed
Godwit.
3-8
Site Description
© Ordnance Survey Ireland. All rights
reserved. Licence number 2010/20
CCMA/ Sligo County Council
Figure 3.3
3.3.2
SPA Designated Areas
Other Designations
3.3.2.1 Proposed Natural Heritage Area
The Natural Heritage Area (NHA) designation was created for the protection of Irish natural
habitats. NHAs are selected by having special scientific significance for one or more
species, communities, habitats, landforms or geological features, or for a variety of natural
attributes and encompass 1,246 sites in Ireland. The NHA regulation has evolved from the
Area of Scientific Interest (ASI) designation and NHAs have statutory protection under the
1976 Wildlife Amendment Act. The statutory body responsible for NHAs is the National
Parks and Wildlife Service of the Department of Arts, Heritage and the Gaeltacht.
There are 630 proposed Natural Heritage Areas (NHAs), comprising 65,000 ha, which were
published on a non-statutory basis in 1995. These and other sites of biodiversity significance
may be designated as NHAs in the coming years. Under the Wildlife Amendment Act (2000)
NHAs are legally protected from damage from the date they are formally proposed for
designation; however these protections are recognised as being more limited than those for
SACs or SPAs. Nonetheless Planning and Licensing Authorities must recognise the
ecological value of pNHAs and ensure that they are protected.
3.3.2.2 Ramsar Wetlands
The Convention on Wetlands of International Importance, especially as waterfowl habitat,
was adopted at Ramsar, Iran in 1971, and is commonly referred to as the Ramsar
3-9
Site Description
Convention. The Convention provides a worldwide framework for the conservation and wise
use of wetlands. Wetlands are areas where water is the primary factor controlling the
environment and the associated plant and animal life. They occur where the water table is at
or near the surface of the land, or where the land is covered by shallow water. Wetlands are
important ecosystems which improve water quality, provide storm protection, provide flood
mitigation, stabilise shorelines, maintain biodiversity, and provide natural products such as
fish and shellfish.
Ireland has designated 45 sites as Wetlands of International Importance pursuant to the
Ramsar Convention. This includes one site within Sligo Harbour, namely Cummeen Strand.
In all cases the Ramsar Wetlands lie within areas designated as Statutory Nature Reserves
or Special Protection Areas (SPAs).
Council
Figure 3.4
pNHA and Ramsar Designated areas
3.3.2.3 EU Designated Shellfish Water
Sligo Harbour supports a regionally important aquaculture industry, with mussels, clams and
oysters being commercially produced. Part of Sligo Harbour has been designated as a
Shellfish Cultivation Designated Area (Figure 3.5), one of sixty four such areas around
Ireland. The aim of the EC Shellfish Waters Directive is to protect or improve shellfish waters
in order to support shellfish life and growth, therefore contributing to the high quality of
shellfish products directly edible by man. It sets physical, chemical and microbiological water
quality requirements that designated shellfish waters must either comply with (‘mandatory’
standards) or endeavour to meet (‘guideline’ standards). Any proposed dredging at Sligo
3-10
Site Description
Harbour should therefore carefully consider the impacts on local water quality in shellfish
producing areas.
Council
Figure 3.5
EU Shellfish Waters
3-11
Site Description
3-12
4.0
Project Description
PROJECT DESCRIPTION
This chapter of the Environmental Appraisal Report describes the main elements and
methodology of the capital and maintenance dredging scheme at Sligo Harbour. The
activities associated with the works and operational characteristics following the completed
dredging are also described.
4.1
EXISTING CONDITIONS
Siltation has taken place in the navigation channel since previous large scale dredging was
carried out in 1998 and the soundings displayed on the Admiralty Charts no longer represent
the current bed level of the channel.
Hydrographic surveys of Sligo Harbour were undertaken in 2007. In May-June 2008 a LiDAR
(Light Detection And Ranging) and multi-beam hydrographic survey of Sligo Harbour,
Drumcliff Bay and Ballysadare Bay was undertaken by the Geological Survey of Ireland and
the Marine Institute in under the INFOMAR project (Integrated Mapping for the Sustainable
Development of Ireland's Marine Resources).
The hydrographic survey carried out for the Sligo Western Bypass has also provided
information on the harbour bed. The current level of hydrographic information is considered
to be adequate for broad assessment of the quantity of dredging that will be required to
achieve the specified depth.
In 2007 renovation of the upstream 1500m of the training wall was carried out and this work
has provided improved definition of the channel. The natural process of siltation continues
and the channel depth is reducing. The most recent surveys indicate that the average bed
depth is now typically in the range -2.2 to -2.8m Chart Datum, although some shallower
areas exist.
The channel widens locally at the Deepwater Jetty to provide a ship turning area. Water
depth in this area has also reduced since previous dredging was carried out. The tide levels
for Sligo Harbour (Oyster Island) are as follows:
Highest Astronomical Tide
Mean High Water Spring Tide
Mean High Water Neap Tide
Mean Low Water Neap Tide
Mean Low Water Spring Tide
Lowest Astronomical Tide
HAT
MHWS
MHWN
MLWN
MLWS
LAT
4.6m CD
4.1m CD
3.0m CD
1.5m CD
0.5m CD
-0.2m CD
Tide levels are established in relation to the Standard Port, Galway.
IBE0440/EAR/September 12
4-1
4.2
Project Description
WATER INJECTION MAINTENANCE DREDGING AT JETTIES TO -2.0m CD
The purpose of the maintenance dredging within the harbour is primarily to facilitate
immediate safe docking and berthing of boats and ships in Sligo Harbour (see Figure 1
Attachment B.2). Currently, the build up of sediment within some areas of the harbour is
resulting in Health and Safety issues associated with docking, with ships observed tilting or
listing when berthed.
This maintenance dredging is required as a result of the natural siltation of the navigation
channel and berths from estuarine sediments. A minimum depth of -2.0m CD at the target
areas is required to reinstate safe berthing. Depths within the dredging area boundary
currently range from +0.5m to -2.5m CD (see see bathymetric survey shown on Drawing 3
and Drawing 3c).
At present, the area immediately downstream of the Deepwater Jetty has only a narrow
channel c. 4 metres wide in which depths achieve -2.0mCD. It is proposed to clear this small
section of the approach channel back to c. 35m in breadth and also to remove small pockets
of siltation immediately in front of the berths. This is the minimum amount of dredging
required to maintain operations at the berths.
4.3
DESIGN OF PROPOSED CAPITAL & MAINTENANCE DREDGING WORKS
TO -3.0mCD
4.3.1 Channel Depth
During a feasibility study prepared by RPS in 2010, it was determined through consultation
with the Harbour Master and Sligo County Council that the proposed dredging works should
be designed to allow vessels with the following criteria a three hour “window of opportunity”
to complete the one hour passage into the port during each tide:
Vessel Characteristic
Design Criteria
Length overall
Beam
Draft
Dead Weight Tonnage
100m
17m
5.9m
4,500 tonnes
At present, the innermost portion of the navigation channel, the area in greatest need of
dredging, between Ballyweelin Point and the Deepwater Jetty, is approximately 30m wide
with a depth generally of 2.2m at LAT. This section of the navigation channel is bounded on
its southern side by a training wall.
The bed level chosen to accommodate a suitable size of vessel in the port is 3 metres below
Chart Datum.
.
.
IBE0440/EAR/September 12
4-2
Figure 4.1: Dredging Area
4-3
IBE00440/EIS01/June 11
Figure 4.2 Dumpsite
IBE00440/EIS01/June 11
4-4
Project Description
4.3.2 Channel Width
The dredging design criteria for the channel cross section have been based on the
requirements of Sligo County Council and the design guide produced by PIANC (1995).
The bottom width of the channel has been determined from the sum of the basic
manoeuvring lane, plus the additional width to account for vessel speed, cross winds, cross
currents, longitudinal currents, wave height, aids to navigation, bottom surface, depth of
waterway plus an allowance for bank clearance. Having regard to the foregoing, a bottom
channel width of 50m has been determined.
4.3.3 Channel Side Slopes
Within the majority of the section of the navigation channel between Ballyweelin Point and
the Barytes Jetty, the bed material is predominantly a fine silty sand. However, the silt
fraction generally decreases and the gravel fraction increases with increasing distance from
the port area. This bed material is typically stable at side slopes of approximately 1 in 5 in
still water conditions and approximately 1 in 11 in active water conditions.
A stability analysis of the channel side slopes undertaken during the 2010 Feasibility Study
indicated that a slope of 1 in 7 should be provided along this section, which maintains a
compromise of pragmatic gradient whilst not over-stretching the dredging footprint
Channel Cross Section Summary
Channel Depth
Channel bottom width
Channel width at direction changes
Channel side slopes
-3.0m CD
50m
50m
1 in 7
Further details on the composition of the bed sediments are presented in Chapter 10,
Geology and Soils.
4.3.4 Channel Alignment
The alignment of the navigation channel is largely determined by existing physical
constraints. These include the training walls extending from Ballyweelin Point to the Barytes
Jetty, Oyster Island and various rock outcrops between Ballyweelin Point and Sligo Bay.
The alignment of the proposed dredged channel will therefore follow very closely the
alignment of the existing channel.
4.3.5 Dredging Quantities
The quantity of dredging required to achieve the stated -3.0m CD depth has been estimated
to be 250,000m³. Figure 4.1 shows the layout of the area proposed for dredging in the
channel, including the turning circle at Deepwater Jetty.
4-5
Project Description
The greater part of this quantity, at approx 55%, lies in the easterly 1500m of channel
nearest the town quays starting from the Barytes Jetty.
The bulk of the remaining 45% lies in the westerly length of channel, approx 2200m long,
from the bend at Old Mill No 14 buoy to Ballyweelin Point. This variation reflects the
increasing depth and width of existing seabed in the outer reaches of the channel. Relatively
small amounts of dredging will also be required to level the section from Ballyweelin Point to
Oyster Island.
4.4
PROPOSED DISPOSAL METHOD
Detailed studies were undertaken to review the alternative means of disposal of the dredged
material (see Section 1.5 of Chapter 1, “Introduction”). Following these studies and
extensive consultation, it was concluded that the only viable solution available for the
disposal of this quantity of material is dumping at sea.
The licensed dump site used to dispose of dredged spoil during the upgrading of Killybegs in
2003 has been closed and no other currently licensed dump site is in operation in or near
Donegal Bay. Therefore an application will be made to the EPA to licence a new offshore
dumpsite for this scheme.
The proposed dump site is located some 34 nautical miles (63 kilometres) from the
deepwater jetty, approximately 17 nautical miles southwest of Malin More Head (Figure 4.2).
Water depths at the site are between 92 and 93 metres Chart Datum.
4.5
DREDGING METHODOLOGY
In European terms, the proposed dredging volumes are not considered to be particularly
great and as such the scheme is likely to be undertaken by a small scale local dredging
company. The specific type of dredger which will undertake the work will therefore not be
known until a contractor has been appointed. There are two types of dredger which could
undertake this work; a suction dredger or a backhoe dredger.
4.5.1 Equipment
4.5.1.1 Suction Dredger
Suction dredgers essentially are suction pumps operating on the seabed which draw in
seabed material along with water and pump the resultant mixture into hoppers on the
dredging vessel or a transport barge (Figure 4.3). This form of dredging therefore draws up
substantial quantities of excess water as well as the sediments. This excess water is either
allowed to overflow the vessel and return to the main body of water, causing a temporary
increase in suspended sediments, or it can be taken out to the disposal site together with the
dredged material. However, it is costly to take an excessive quantity of water to sea.
4-6
Project Description
4.5.1.2 Backhoe Dredger
A backhoe or mechanical dredger involves the use of hydraulic grab or bucket to loosen the
in situ material, then raise and transport it to the surface (Figure 4.4). Dredging with
hydraulic excavators is a slower process, but reduces the amount of excess water which is
extracted. A backhoe dredger will sometimes transfer the dredged sediments into a
transporting barge, rather than carrying the sediment itself.
Figure 4.3
Example of a Trailing Suction Dredger
Figure 4.4
Example of a Backhoe Dredger
4.5.2 Dredging Programme
The water depths in the existing channel are such that it is likely that the dredger will have to
dig its way upstream and that it will only be able to dredge during the upper half of the tidal
cycle.
4-7
Project Description
The dredger size will be limited by the constraints within the channel and economies of scale.
It is likely that a dredger with a laden capacity of up to 1,500m³ would be suitable for this
scheme. Dependent on how much of the supernatant water is allowed to overspill from the
dredger, between 500m³ and 1050m³ of sediments could be transported to the dumpsite per
dredging cycle. It is assumed that the dredger will rotate personnel in shifts and operate on a
24hr basis, as this would be the most economic option, allowing between 1,000m³ and
2,100m³ to be dredged per day. The dredging operations could therefore take between 4
and 8 months, dependent on the dredger. Adverse weather conditions would increase the
length of time taken.
For each tide (approx 12.4 hours) the dredger will only be able to dredge for around 70-80
minutes. The rest of the time it will be steaming to and from the dump site. A typical dredger
would travel at an average speed of 6.5 knots laden and 8 knots unladen, therefore taking
around 10 hours in normal conditions to for a return trip to the dump site, including the time
taken to discharge the sediments.
4.5.3 Personnel
During the dredging it is anticipated that operations will occur on a 24hr basis. Typically, a
dredging project of this scale would have a total of seven personnel in total crewing the
dredger, working in shifts with four or five personnel on board at any one time and two or
three on shore. Those on board would live on the ship. In line with best practice, at all times
at least one of the personnel on board should be a qualified marine mammal observer
(MMO).
4.5.4 Navigation
As the dredging will occur within the existing navigation channel, no amendments or
additions to the existing navigation markers in Sligo Harbour are envisaged.
4.5.5 Waste
All rubbish to be disposed of from the dredger vessel will be handled and disposed by a
licensed waste disposal contractor. Waste awaiting disposal will not be permitted to be
stored on the quayside.
Discharges from the vessel to the harbour waters will not be permitted
4-8
5.0
BIRDS
5.1
BACKGROUND
Birds
Maintenance dredging of the berths and navigation channel in Sligo Harbour, from the
Barytes Jetty to the eastern end of Oyster Island, is required in order to maintain the
minimum required depth for current vessels using Sligo Harbour. Capital dredging along
lengths of the channel is required in order to generate new business and thereby secure the
future viability of Sligo Harbour as a destination for commercial vessels.
Natura Environmental Consultants Ltd was commissioned to undertake baseline surveys, in
the winter 2009/10 and summer/autumn 2010, of non-breeding birds likely to be affected by
the proposed dredging of the shipping channel along the northern edge of the estuary. The
entire area of Sligo Harbour, below Mean High Water Mark (MHWM) is designated as a
Special Protection Area (SPA) under the terms of the EU Birds Directive (79/409/EEC) and
as a Special Area of Conservation (SAC) under the EU Habitats Directive (92/43/EEC). This
chapter covers the impacts of the scheme on birds and includes an Appropriate Assessment
under Article 6(3) of the Habitats Directive.
5.1.1 Description of Proposed Works
The area to be dredged represents in total a 5.3km length of the navigation channel from
Oyster Island to the Barytes Jetty. The greatest proportion of dredging activity will take place
in the easternmost section of the navigation channel, the 1.5km stretch between the Old Mill
and the Barytes Jetty.
The bottom sediments within the navigation channel comprise of fine sand and silt and no
rock breaking or blasting activities are envisaged. Sediment testing has been undertaken
which has confirmed that the dredged sediment is free of contaminants and is suitable for
dumping at sea, and the dredger is expected to take one load to the dump site per tide.
In the operation phase, the dredging will permit vessels with a draft of 5.2m to access the
Barytes and Deepwater Jetties for a greater portion of the tidal cycle. A detailed description
of the proposed works is provided in Chapter 4 of this Appraisal Report, “Project
Description”.
5.1.2 Previous Information
Sligo Harbour has been covered by regular counts of wintering birds since the 1970s.
Hutchinson (1979) reported that very large flocks of wigeon and brent geese appear at times
in September and October on Cummeen Strand, on the south side of the Harbour. In the
1970s this was considered the best wader area in Sligo Bay with the most numerous species
being oystercatcher (up to 700 in late autumn), ringed plover (up to 200), curlew (up to 300),
bar-tailed godwit (up to 180), redshank (up to 160) and dunlin (up to 200) (Hutchinson 1979).
5-1
Birds
Since the mid 1990s, the bay has been continuously monitored as part of the national
IWeBS survey (Crowe 2005). Up to 2000/01 numbers of water birds overall had remained
consistent since the mid 1980s (Sheppard 1993) with a marginal 6% decline. However, there
had been several changes at species level. Substantial declines were reported in the
numbers of wintering brent geese and ringed plover while grey heron, red-breasted
merganser and bar-tailed godwit had also declined. Increases had occurred in this period in
shelduck, mallard, golden plover, lapwing, curlew, redshank and turnstone (Crowe 2005).
The total area of Sligo Harbour is still regularly counted for IWeBS and the peak counts for
each species for the last five available winters are given in Table 5.1.
More applied studies of birds in Sligo Harbour were undertaken in connection with the
proposed reconfiguration of Sligo Airport Runway (RPS Consulting Engineers). This study
covered the winter of 2007/08 and counts were conducted in the area of Dorrins Strand (at
the south-west of Cummeen Strand) at intervals of 2 weeks over the period 22 November
2007 to 16 March 2008. During each visit, counts were conducted at hourly intervals
between first light and dusk. In addition to the above, counts of the whole of Sligo Harbour
were carried out at monthly intervals from November 2007 to March 2008 inclusive. Subsites used during the visits were identical to those used by IWeBS (Crowe 2005).
5.2
ASSESSMENT METHODOLOGY
5.2.1 Legislation and guidance
Flora and fauna in Ireland are protected at a national level by the Wildlife Act, 1976 and
Wildlife (Amendment) Act, 2000 and the Flora (Protection) Order, 1999 (SI 94/1999). They
are also protected at a European level by the EU Habitats Directive (92/43/EEC) and the EU
Birds Directive (79/409/EEC) which are transposed into Irish law by the European
Communities (Birds and Natural Habitats) Regulations, 2011 (S.I. No 477 of 2011).
5.2.2 Consultations
Consultations were undertaken with the Development Applications Unit (DAU) of the
Department of the Environment, Heritage and Local Government in 2009 (now part of the
Department of Arts, Heritage and the Gaeltacht). The response received from the DAU
(G2009/591) noted that the proposed works were to take place within the Natura 2000 sites
Cummeen Strand SPA and Cummeen Strand/Drumcliff Bay cSAC and identified the
following potential impacts:
x
x
x
Direct loss of habitat due the excavation and removal of material from the Special Area
of Conservation;
Risks from inappropriate disposal of dredge material;
Direct disturbance to wildfowl.
The response also recommended that special consideration be given to a number of issues
in the Environmental Impact Assessment, summarised as follows (the full consultation
response is included as Appendix 2C);
5-2
x
x
x
x
x
Birds
The intertidal and sub-tidal habitats that may be affected by the scheme.
Disturbance to wildfowl within Sligo Harbour.
The storage site for the dredged material, if it is to be re-used in future building projects.
The reclamation of land within Cummeen Strand and the disposal of dredged material.
Beach nourishment and the possibility of disposing of suitable dredge material within
the Sligo Bay coastal system.
The response considered that appropriate assessment, as outlined in Article 6(3) of the EU
Habitats Directive 92/43/EEC, would be required as part of this proposal. The Screening for
Appropriate Assessment in relation to Cummeen Strand SPA is included as Appendix 3B to
this Environmental Appraisal Report.
Consultations were also undertaken with BirdWatch Ireland in relation to Irish Wetland Bird
Survey (IWeBS) bird count data for Sligo Harbour/Cummeen Strand.
5.2.3 Desktop review
A desktop review was carried out of all available bird count data for the study area in the
most recent 5-year period, 2003/04 to 2007/08. These counts were provided by BirdWatch
Ireland and form part of the Irish Wetland Bird Survey (IWeBS). In addition, the counts
carried out on behalf of RPS Consulting Engineers for the proposed reconfiguration of Sligo
Airport Runway were reviewed. These covered the winter of 2007/2008. The National Parks
and Wildlife Service was consulted in relation to the proposed project and the conservation
objectives of the designated areas.
5.3
FIELD SURVEYS
The methodology for the field surveys was as follows: the area of the proposed dredging
was surveyed at monthly intervals from December 2009 to March 2010 inclusive and from
June to November 2010. On each visit, counts were conducted within 2 hours either side of
low tide and within 2 hours either side of high tide. The area covered coincided with subsites 3, 4 and 6 of the IWeBS survey sites (Crowe 2005) and essentially covered the
shipping channel and any intertidal areas within 1km of its boundaries (Figure 5.1). This
included the areas known as the inner harbour, Cartron Strand, Standalone Point, the
northern part of Cummeen Strand and the shoreline from Ballincar to Rosses Point,
including the channel north of Oyster Island. In addition to the monthly counts on the
shipping channel, a single low tide count of the entire Sligo Harbour was undertaken in
January 2010 to provide an overall context for the regular monitoring. All counts were
undertaken in reasonable to good visibility using a 34x telescope.
5-3
Birds
Figure 5.1: Area of the shipping channel surveyed as part of the bird surveys over the
period December 2009 – November 2010
5.4
ECOLOGICAL EVALUATION AND IMPACT SIGNIFICANCE
The prediction of impacts/impact significance is based upon the guidance provided in the
EPA guidance document Guidelines on the information to be contained in Environmental
Impact Statements (2002), and considers such factors as the character of the impact, its
magnitude, extent, and duration and the probability of such an impact occurring. From these
criteria the significance of the impact is determined on the basis of the factors which
characterise the site/receptor and take into account the effects on the conservation status or
integrity of the site resulting from the proposed development. The integrity of a site can be
regarded as the coherence of ecological structure and function, across the entirety of a site,
which enables it to sustain all of the ecological resources for which it has been valued. The
following impact significance criteria (EPA, 2002) are used where applicable:
5-4
Significance
Impact
Imperceptible
impact
Slight impact
Moderate impact
Significant impact
Profound impact
5.5
Birds
of
Significance Criteria
An impact capable of measurement but
without noticeable consequences
An impact which causes noticeable changes
in the character of the environment without
affecting its sensitivities
An impact that alters the character of the
environment in a manner that is consistent
with existing and emerging trends
An impact which, by its character,
magnitude, duration or intensity alters a
sensitive aspect of the environment
An impact which obliterates sensitive
characteristics
BASELINE ENVIRONMENT
5.5.1 Designated Areas for Nature Conservation
In 1995, the entire intertidal area of Sligo Harbour, from Sligo town to beyond Coney Island,
was designated as a Special Protection Area (SPA) under Article 4 of the EU Birds Directive
(79/409/EEC) (Statutory Instrument 31/1995). The area covered by the Special Protection
Area designation has increased in the interim according to a notice issued on 12th March
2010 by the Department of the Environment, Heritage and Local Government and the
existing Cummeen Strand SPA boundary is shown below (Figure 5.2).
Figure 5.2: Cummeen Strand SPA boundary (updated February 2012)
5-5
Birds
5.5.2 Cummeen Strand SPA (Site Code 004035).
Cummeen Strand is a large shallow bay stretching from Sligo town westwards to Coney
Island. It is one of three estuarine bays within Sligo Bay, with Drumcliff Bay to the north and
Ballysadare Bay to the south. The Garavogue River flows into the bay and forms a
permanent channel.
At low tide, extensive sand and mud flats are exposed. These support a diverse macroinvertebrate fauna which provide the main food supply for the wintering waterfowl.
Invertebrate species such as lugworm (Arenicola marina), ragworm (Hediste diversicolor),
cockles (Cerastoderma edule), sand mason (Lanice conchilega), Baltic tellin (Macoma
balthica), spire shell (Hydrobia ulvae) and mussels (Mytilus edulis) are frequent. Of particular
note is the presence of eelgrass (Zostera noltii and Z. angustifolia) beds, which provide a
valuable food stock for herbivorous wildfowl. The estuarine and intertidal flat habitats are of
conservation significance and are listed on Annex I of the EU Habitats Directive. Areas of
salt marsh fringe the bay in places and provide roosting sites for birds during the high tide
periods. There are sand dunes at Killaspug Point and Coney Island, with a shingle spit at
Standalone Point near Sligo town.
Cummeen Strand is of ornithological importance as it supports important concentrations of
wintering waterfowl. The site supports an Internationally Important flock of Brent Geese
(peak of 232 individuals in the winter of 1999/00, with the mean of peak monthly counts in
the period 1996/99 (except 1998) being 228, peaking at 309) and Nationally Important
populations of a further two species – Oystercatcher 891 and Redshank 501 (all figures are
average peaks for the period). Other species which occurred in significant numbers included
Shelduck 80, Wigeon 178, Teal 70, Mallard 170, Red-breasted Merganser 17, Golden Plover
567, Lapwing 734, Knot 18, Sanderling 18, Dunlin 601, Bar-tailed Godwit 57, Curlew 546,
Greenshank 18 and Turnstone 80. Whooper Swans also occurred (9), though they are not
regular visitors. The presence of Golden Plover, Bar-tailed Godwit and Whooper Swan is of
particular note as these species are listed on Annex I of the EU Birds Directive.
This site is of high ornithological importance, with one species having a population of
International Importance and two having populations of National Importance. In addition,
there are three species that are listed on Annex I of the Birds Directive. The site is also
important as a component of the much larger Sligo Bay complex.
Qualifying Interests:
x
Light-bellied Brent Goose (Branta bernicla hrota) [A046]
x
Oystercatcher (Haematopus ostralegus) [A130]
x
Redshank (Tringa totanus) [A162]
x
Wetlands & Waterbirds [A999]
Wintering
Wintering
Wintering
Conservation Objective: To maintain or restore the favourable conservation condition of the
bird species listed as Special Conservation Interests for this SPA.
5-6
Birds
5.5.3 Cummeen Strand/Drumcliff Bay candidate SAC (site code 0627)
The entire intertidal area of Sligo Harbour, together with Drumcliff Bay, is also designated as
a candidate Special Area of Conservation (cSAC). A description of the cSAC and the
potential impacts of the proposed dredging works on it, are discussed in Chapter 6 of the
Environmental Appraisal Report and in the Natura Impact Statement for Cummeen
Strand/Drumcliff Bay cSAC (Appendix 4A).
5.5.3.1 Implications of the SPA and cSAC designations for any development
In order to protect ecologically important sites, certain potentially harmful works are
restricted within SPAs and cSACs. These works (known as activities requiring consent,
damaging activities or operations requiring consent) are works liable to destroy or to
significantly alter, damage or interfere with the ecology of the site. Among the activities
requiring consent are:
x
Altering watercourses or wetlands, including changing the height of the water table,
blocking or altering the flow of water or deepening any channel.
In respect of the activities requiring consent, there is no requirement to obtain the consent of
the Minister, if the said activity is licensed by or subject to the permission of another Minister,
Public Body, State of Local Authority or specified as permitted in an approved farm plan for
the land in question (from Notice of Intention to designate Cummeen Strand (Site code
004035) County Sligo as a Special Protection Area (SPA).
As the entire area of the shipping channel is covered by the SPA and cSAC designations
(which are part of the Natura 2000 network of protected sites) there is a requirement for
Appropriate Assessment of the likely impacts of the proposed dredging works. This is in
accordance with Article 4 of the European Directive 2009/147/EC on the conservation of wild
birds, known as the “Birds Directive” and Article 6(3) of the European Directive 92/43/EEC,
known as the “Habitats Directive”. The Appropriate Assessment process follows the
guidance published by the Department of the Environment, Heritage and Local Government
(2009).
A Screening for Appropriate Assessment was carried out for the proposed development. The
screening report concluded that there will be no risk of significant negative effects on
Cummeen Strand SPA, either alone or in combination with other plans or projects, and
therefore, no adverse effect on the integrity of the Natura 2000 site or on its conservation
objectives as a result of the proposed works. Therefore, Stage 2 of the Appropriate
Assessment process (Natura Impact Statement] is not required. The full Screening for
Appropriate Assessment report is included in Appendix 3B.
5-7
5.6
Birds
DESCRIPTION OF EXISTING BIRD POPULATIONS AND USAGE OF THE
AREA
5.6.1 General description of the study area
Sligo Harbour lies in the centre of a group of three estuaries that comprises Sligo Bay. Also
known as Cummeen Strand, it forms the estuary of the Garavogue River. It is protected
from the open sea by Coney Island at the western end and by the smaller Oyster Island,
which lies in the mouth of the main channel near Rosses Point. The existing shipping
channel runs along the northern edge of Sligo Harbour, while to the south of the estuary
there are large undivided areas of sand and mudflats. There is a natural shingle spit at
Standalone Point between Cartron and Ballincar. This protects an area of finer muds in
Cartron Bay.
Bird populations and their usage of the estuary are described below in relation to three
different units as follows:
1. The entire area of Sligo Harbour (also known as Cummeen Strand);
2. The shipping channel and all intertidal areas within 1km of the channel;
3. The shipping channel and its banks only.
5.6.2 Bird populations of the entire area of Sligo Harbour
The best available information on the bird populations of the entire area of Sligo Harbour is
provided by the Irish Wetland Bird Survey (IWeBS), organised by BirdWatch Ireland. Table
5.1 gives the peak counts for a series of five winters (2005/06 to 2009/10), the latest
complete information available. This shows that Sligo Harbour is of international importance
for light-bellied brent goose and of national importance for three species of wader
(oystercatcher, knot and bar-tailed godwit).
The most significant low tide feeding areas are on the intertidal mudflats which extend south
from the shipping channel to the southern shoreline of the bay and west as far as Coney
Island. Another important concentration of feeding birds occurs in Cartron Bay to the north
of the shipping channel.
Table 5.1:Irish Wetlands Bird Survey (IWeBS) peak counts in Sligo Harbour (entire
estuary).
(Mean is the average of the peak counts in the last 5 winters)
Species
Mute Swan
Whooper Swan
Brent Goose
Ruddy Shelduck
2005/06
2006/07
2007/08
2008/09
2009/10
Peak
Mean
20
26
38
36
14
38
27
0
0
0
1
0
1
0
331
663
331
543
433
663
460
0
0
0
0
1
1
0
Shelduck
60
45
94
118
120
120
87
Wigeon
84
153
337
108
62
337
149
Gadwall
0
0
0
1
0
1
0
75
22
108
73
15
108
59
Teal
5-8
Species
Mallard
Birds
2005/06
2006/07
2007/08
2008/09
2009/10
Peak
Mean
156
202
185
301
148
202
198
Scaup
0
0
0
6
0
6
1
Long-tailed duck
0
0
0
0
1
1
0
10
0
0
2
0
10
2
120
1
0
0
0
120
24
6
8
9
15
3
15
8
23
13
35
37
23
37
26
0
0
0
0
1
1
0
Eider
Common Scoter
Goldeneye
Red-breasted Merganser
Ruddy Duck
Red-throated Diver
3
2
4
1
6
6
3
14
1
10
13
15
14
11
Little Grebe
0
3
3
2
3
3
2
Great Crested Grebe
2
2
20
6
7
20
7
Cormorant
23
16
26
16
16
26
19
Shag
Great Northern Diver
21
2
15
19
4
21
12
Little Egret
0
0
0
1
3
3
1
Grey Heron
18
23
24
25
11
25
20
Oystercatcher
759
684
1011
678
987
1011
824
Ringed Plover
165
173
157
93
127
173
143
Golden Plover
350
0
363
654
9
654
275
Grey Plover
67
0
20
11
80
80
36
Lapwing
59
438
216
341
111
438
233
700
346
1400
523
950
1400
784
98
41
10
110
0
110
52
Dunlin
601
477
2079
945
662
2079
953
Snipe
9
0
0
0
8
9
3
Knot
Sanderling
Black-tailed Godwit
2
40
0
8
1
40
10
Bar-tailed Godwit
960
277
236
233
438
960
429
Curlew
479
297
292
529
480
480
415
8
9
16
10
9
16
10
Redshank
191
74
335
482
376
482
292
Turnstone
72
12
96
32
191
191
81
Unidentified wader sp.
0
0
0
35
0
35
7
Mediterranean Gull
0
0
0
1
0
1
0
554
452
500
717
234
717
491
1
1
0
1
0
1
1
373
298
338
370
122
373
300
0
3
0
0
0
3
1
Herring Gull
55
118
160
135
168
168
127
Iceland Gull
0
0
0
1
1
1
0
Glaucous Gull
0
0
0
7
0
7
1
Great Black-backed Gull
4
21
13
26
11
26
15
Greenshank
Black-headed Gull
Ring-billed Gull
Common Gull
Lesser Black-backed Gull
(data supplied by BirdWatch Ireland on behalf of National Parks and Wildlife Service).
* If the 5-year mean peak exceeds 1% of the national or international populations of a species, the site is classified as of either
national or international importance (Boland and Crowe 2012). Significant population figures are underlined.
5-9
Birds
5.6.3 Bird usage of the area within 1km of the shipping channel
Intertidal areas within 1km of the shipping channel, including the inner harbour, east of
Barytes Quay, and the channel north of Oyster Island were included in the regular monthly
counts carried out from December 2009 to November 2010. This area was included to
enable assessment of possible indirect effects of dredging on the shipping channel.
On either side of the shipping channel, there are extensive intertidal mudflats and sandflats
exposed at low tide. The area to the south-east of the channel, known as Cummeen Strand,
holds large flocks of brent goose, shelduck, bar-tailed godwit, curlew and dunlin. The
sheltered mudflats within Cartron Bay, north-east of the harbour, are also important at low
tide for a range of wildfowl and waders, particularly brent goose, curlew, redshank,
oystercatcher and lapwing. In the inner harbour, between the shipping quay and the N15
road bridge, a small number of waders are found with moderate numbers of gulls and a
resident flock of mute swan.
The most important high tide roosts on the northern side of the channel are on the southern
and eastern sides of Standalone Point. This area, opposite the existing port, is particularly
used by birds in strong westerly winds when it provides a degree of shelter. The main
species roosting here include grey heron, oystercatcher, lapwing, bar-tailed godwit, curlew,
redshank, greenshank and turnstone. There are also other smaller high tide roosts on the
east side of Cartron Bay, along the northern shore of the channel between Ballincar and
Rosses Point and occasionally on the training wall south of the channel.
A total of 27 species of waterbirds was recorded within this count area over the period of
December 2009 to November 2010. This includes ten species of wildfowl (and allies), ten
species of waders, five species of gull, together with cormorant and grey heron. Tables 1
and 2 in Appendix 3A, give the full counts of this area while Table 5.2 below gives a
summary of the mean and peak numbers of each species occurring at low tide and high tide.
The peak figure represents the maximum number of birds recorded at any one time during
the winter counts. The peak counts for each species occurred on different dates. The highest
total count of all species at low tide was 3,295, recorded in November 2010. The highest
total count of all species at high tide was 716, also recorded in November 2010.
For most species of wildfowl and waders, numbers are greater at low tide as more of the
intertidal area is exposed. At high tide the birds move to a few key roost sites and some
leave the area of the channel completely. For diving species such as cormorant, redbreasted merganser and great crested grebe, some birds were present on all states of the
tide as they are mainly confined to the channel.
5-10
Birds
Table 5.2: Summary of peak and mean numbers of water birds within 1km of the
shipping channel in Sligo Harbour over ten months, December 2009-November 2010.
Low tide
High tide
10
10
Number of counts
Species
Mute Swan
Brent Goose
Peak
Mean
Peak
Mean
50
14
45
15
225
78
155
22
Shelduck
48
8
2
0
Wigeon
62
20
53
15
Teal
70
11
40
4
155
64
94
56
4
1
2
0
14
3
17
2
1
0
2
0
Mallard
Goldeneye
Great Crested Grebe
11
2
3
1
Cormorant
31
8
16
7
Grey Heron
18
8
14
3
212
102
222
54
1
0
0
0
40
12
50
12
4
0
0
0
280
39
83
9
Dunlin
20
152
0
0
Curlew
432
134
271
85
5
2
13
2
Redshank
511
173
200
89
Turnstone
6
1
124
28
380
128
90
26
32
7
14
5
3
1
7
1
70
30
52
16
5
2
9
3
Oystercatcher
Grey Plover
Lapwing
Black-tailed Godwit
Bar-tailed Godwit
Greenshank
Black-headed Gull
Common Gull
Herring Gull
5.6.4 Bird usage of the shipping channel and immediate banks only
In order to assess the direct disturbance effects of dredging on the birds using the shipping
channel, an analysis was made of species and numbers using only the channel and its
immediate banks. A summary of this information is given in Table 5.3.
The central part of the channel is permanently covered by water even at low tide. It is used
by a few cormorant, great northern diver, red-breasted merganser and great crested grebe,
which are all fish-eating species. The edges of the channel are used for swimming and
feeding by various wildfowl including light-bellied brent goose, shelduck, wigeon, teal and
5-11
Birds
mallard. Gulls are also generally present including black-headed, common, herring and great
black-backed gulls.
The edges of the shipping channel are marked (in the eastern part in particular) by a line of
rocks creating a breakwater along the sides of the channel. This is exposed at low tide and
at neap high tides but largely covered at high spring tides. It provides an important roost site
on some dates for significant flocks of redshank, oystercatcher and turnstone. The birds are
sometimes present at low tide as well as high tide. Isolation from ground predators and other
disturbance, together with proximity to intertidal feeding areas are the principal attractions of
this breakwater for birds.
Table 5.3: Summary of peak and mean numbers of water birds on the shipping
channel and its immediate banks in Sligo Harbour over ten months, December 2009November 2010.
Number of counts
Species
Low tide
High tide
10
10
Peak
Mean
Peak
Mean
50
9
31
5
184
33
25
4
2
0
0
0
Wigeon
62
11
28
6
Teal
70
8
0
0
Mallard
37
9
48
13
Goldeneye
10
0
2
0
10
2
8
1
1
0
0
0
Mute Swan
Brent Goose
Shelduck
Great Crested Grebe
2
1
3
0
Cormorant
13
3
10
3
Grey Heron
6
3
2
1
164
49
222
32
Lapwing
10
1
0
0
Bar-tailed Godwit
10
1
80
8
Curlew
19
6
42
9
5
1
0
0
Redshank
230
24
106
14
Turnstone
6
1
120
27
Black-headed Gull
0
0
1
3
Common Gull
0
0
14
1
0
0
2
0
24
5
3
1
1
0
3
0
Oystercatcher
Greenshank
Herring Gull
The following species are of particular note, in the area of the shipping channel and its
banks.
5-12
Birds
Mute swan: A flock of mute swan regularly feeds in winter in the inner harbour area where
they benefit from artificial food sources. In later summer they appear to disperse into the
estuary and a peak of 50 birds was recorded in July 2010 in the mid-channel area near
Ballincar.
Brent goose: A significant part of the brent goose flock uses the northern part of the bay on
both sides of the shipping channel. A peak of 184 was recorded in this area in November
2010. They occasionally use Cartron Bay and have been recorded in the channel north of
Oyster Island. Small flocks of brent geese feed along the northern shore of the channel
throughout the winter, especially where minor freshwater streams enter the bay.
Wigeon: A peak of 62 wigeon was recorded in the immediate area of the shipping channel.
These regularly feed in the area south of Standalone Point and at various locations along the
northern shore of the channel in smaller numbers.
Teal: A peak count of 70 teal in the shipping channel area was recorded at low tide. At high
tide the birds often move into vegetated areas and become difficult to see and identify. The
main feeding areas are around Standalone Point.
Mallard: Mallard are generally scattered in small flocks all along the northern bank of the
shipping channel. The principal feeding areas are at the mouth of Cartron Bay and at
Ballincar.
Red-breasted merganser: A small number of merganser use the shipping channel for
feeding.
Great crested grebe: A small number of grebe use the shipping channel for feeding.
Cormorant: Cormorant are usually present in small numbers throughout the channel. They
roost on the training walls, on the navigation marks and on the eastern end of Oyster Island.
Grey Heron: Herons are widely distributed in small numbers along the banks of the channel.
The main high tide roost is on Standalone Point.
Oystercatcher: This common wader species is normally present along the channel in
higher numbers at low tide. Unusually large roosts were recorded at the southern end of
Standalone Point (220 in October 2010) and on the southern training wall (83 in March
2010).
Curlew: The highest numbers of curlew are found near the shipping channel at high tide
when they roost on the southern end of Standalone Point.
Redshank: Small numbers of redshank feed along the channel at low tide. Significant
numbers are usually present in Cartron Bay and they use the training walls on the south side
of the shipping channel as a roosting site.
5-13
Birds
Turnstone: Turnstone are often well camouflaged in the more gravely areas of the channel
banks. They use the training walls on either side of the shipping channel and the southern
end of Standalone Point as roosting sites (peak of 120 recorded in October 2010).
5.7
PREDICTED IMPACTS OF THE PROPOSED DREDGING
5.7.1 Potential impacts on birds
The following are the individual elements of the proposed development which could
potentially give rise to adverse effects on waterbirds within Sligo Harbour/Cummeen Strand;
x
x
x
x
x
The physical act of dredging by the dredging vessel and its crew has the potential to
cause some temporary disturbance to waterbird populations in Sligo Harbour.
The dredging will result in the removal of sediments from the estuary along the shipping
channel. This will result in the loss of some sub-tidal and intertidal habitat and has the
potential to impact on the training walls along the shipping channel, which are an
important roost site for waterbirds.
The dredging will result in the removal of sediments from the estuary along the shipping
channel. This will impact directly on the benthic environment and has the potential to
negatively impact on the infaunal macrobenthos which acts as important food source for
waterbird species in the estuary.
The dispersion and settlement of sediment released during the dredging works has the
potential to cause impacts directly on the intertidal environment (habitats and fauna)
within Sligo Harbour and also may have associated indirect impacts on waterbird
species within the SPA.
The disposal of the dredged material has the potential to impact on the intertidal
environment (habitats and fauna) within Sligo Harbour.
5.7.2 Likely direct impacts on birds
Dredging activities have the potential to cause some temporary disturbance to
waterbird populations in Sligo Harbour.
There is potential for the disturbance of waterbirds as a result of noise, vibration and
dredging activity associated with the construction phase of the project. However, waterbirds
within Sligo Harbour/Cummeen Strand are unlikely to be significantly disturbed by the
dredging activities as the disturbance will be localised and short-term in nature. For each
tidal cycle (approx 12.4 hours) the dredger will only be able to dredge for around 70-80
minutes. The rest of the time it will be travelling to and from the proposed dump site
(approximately 50km away, offshore). A typical dredger would travel at an average speed of
6.5 knots laden and 8 knots unladen, therefore taking around 10 hours in normal conditions
to for a return trip to the dump site, including the time taken to discharge the sediments (for a
full description of the proposed works, see Chapter 4, Section 4.4.2 of this document).
5-14
Birds
Bird species in the harbour are already subject to disturbance from recreation, transport
(shipping movements in the harbour and low flying aircraft in the area of Sligo Airport) and
other activities and appear to be habituated to current levels of disturbance.
Given the factors discussed above, disturbance to waterbird species as a result of the
proposed dredging activities (either alone or in combination with existing disturbance levels)
will result in an imperceptible impact. It is extremely unlikely to have a significant negative
effect on waterbirds within Sligo Harbour/Cummeen Strand, even in the short term.
The dredging will result in the removal of sediments from the estuary along the
shipping channel. This will result in the loss of some sub-tidal and intertidal habitat.
This also has the potential to impact on the tidal regime in Sligo Harbour.
Direct loss of habitat
The proposed works will require the removal of predominantly sub-tidal substrate within the
existing deep water channel in Sligo Harbour. However, the proposed works will also require
the removal of a small area (c. 31,811m² or 0.07% of the overall cSAC area1) of intertidal
material (fine silts and sands) inside the training wall between Ballyweelin Point and the
Deepwater Jetty. A total estimated volume of 250,000m3 of sediment will be removed from
the estuarine environment in Sligo Harbour during the course of the proposed work. This
material will be removed from an area that has been the subject of previous large scale
dredging works (in 1998) and exists as a maintained channel at this location, which is
delineated by man-made training walls at its outer edges. The removal of this material will
not have a significant negative effect on the estuary and will not destabilise the structure or
functioning of the estuary relative to existing conditions. From observations made during the
field surveys, the intertidal area between the training walls along the deep water channel is
not of great importance for birds within the estuary as a whole. The volume of sediment to be
removed is not significant in the context of the total available sediment within the SPA and
will not have any significant effect on the habitats, or on the waterbirds, within the estuary.
The training walls along the shipping channel are an important roost site for waterbirds in
Sligo Harbour. However, the training walls will not be directly impacted by the proposed
dredging works.
A literature review was undertaken as part of this assessment to find any examples of
recorded impacts of dredging activity on estuarine birds elsewhere. An assessment of
potential impacts of both capital and maintenance dredging on birds in the Tamar Estuary,
south-west England was published (Widdows et al. 2007). Maintenance dredging in the
lower Tamar typically accounts for the annual removal of between 5,000 and 200,000 tonnes
of dry sediment per year. During periods of capital dredging, the amount of sediment
dredged increased significantly to between 500,000 and 700,000 tonnes per year. The study
reviewed population data for ten bird species, including mallard, shelduck, teal, wigeon,
curlew, dunlin, oystercatcher and redshank, over a 30-year period from 1971 to 2002. None
of the wildfowl or wader species studied showed any correlation between bird numbers and
1
The area of the cSAC (48,541,373 m²) has been calculated using the geodatabase file of the Cummeen Strand/Drumcliff Bay
(Sligo Bay) SAC polygon (v1.04) as published on the National Parks and Wildlife Service data maps viewer
http://webgis.npws.ie/npwsviewer/ on 21 June 2012
5-15
Birds
dredging activity in the Tamar. There were no marked changes in numbers during the year
of peak dredging or during the following winters. Declines in teal and wigeon were
considered to be related to a series of milder winters reducing their need to migrate as far as
south-west England.
Given the factors discussed above, the removal of intertidal and sub-tidal material as a result
of the proposed dredging activities will result in a slight impact in the short-term in the
immediate area. However, the impact will reduce to an imperceptible impact within a short
period, particularly when taken in the context of the estuary as a whole and the wider
complex of estuarine habitats that make up Sligo Bay. It is extremely unlikely to have a
significant negative effect on waterbirds within Sligo Harbour/Cummeen Strand, even in the
short term.
5.7.3 Impacts on the Tidal Regime of Sligo Harbour
Hydrodynamic modelling was undertaken as part of the study to investigate the impact of the
dredging on the hydraulic regime of Sligo Harbour and on the sedimentation in the harbour
area during the dredging operations (Chapter 11, Coastal Processes). The modelling was
used to examine the effect of:
x
x
The change in channel bathymetry on the tidal flows and water levels, and
The dispersion and fate of material spilled during the period of the dredging operations.
Dredging works will involve some temporary suspension of fine sediments in the water
column within Sligo Bay (refer to Chapter 11.1 and 11.2).
The results of the tidal flow modelling indicate that while the proposed dredging will lower the
level of the low water spring tides in the channel at Sligo (caused by the removal of the bar
within the shipping channel by the proposed dredging) the high spring tide level will be
unaffected by the proposed dredging works. At present, this bar slows down the passage of
water exiting the channel at low tide, causing some water be retained or pooled behind it. If
the bar is dredged, the water will be able to drain more freely at low tide, thus causing lower
water levels and possible drying out of the channel upstream of the bar at extreme low
spring tides. As can be seen on Figure 11.18 of Chapter 11 of this document, this drying will
last for a maximum of 2 hours. It is not considered that this will result in any significant
negative effect on waterbird populations in Sligo Harbour or have an adverse affect on the
structure and functioning of the estuary.
The impact of the proposed dredging on the flow regime in Sligo Harbour has been
assessed by comparing the mean and peak flow velocities for both flood and ebb tides.
Figures 11.19 and 11.21 of this report show the difference in the mean tidal velocity for both
flood and ebb spring tides. In these diagrams, the difference in the tidal velocity is calculated
by comparing the average tidal velocity over the flood or ebb period for the model with the
dredged channel in place and subtracting the equivalent flows for the model with the existing
bathymetry. These diagrams show that the difference in the mean velocities is generally very
5-16
Birds
small (less than 0.1 m/s) and the changes are restricted to the area around the channel and
the northern section of the harbour area. As such, the impact of the dredging will have an
imperceptible effect on the current flows in the harbour area except in the area of the
channel itself, where increases of up to 0.4m/s may be experienced in localised areas, and
the area north of the navigation channel may be slightly decreased by around 0.1m/s.
Given the factors discussed above, the removal of intertidal and sub-tidal material as a result
of the proposed dredging activities will result in an imperceptible impact on the tidal regime
of Sligo Harbour. It is not considered that this will result in any significant negative effect on
waterbird populations in Sligo Harbour or have an adverse affect on the structure and
functioning of the estuary.
5.8
LIKELY INDIRECT IMPACTS ON BIRDS
The dredging will result in the removal of sediments from the estuary along the
shipping channel. This will impact directly on the benthic environment and has the
potential to negatively impact on the infaunal macrobenthos which acts as an
important food source for waterbird species in the estuary.
There will be a loss of benthic habitat along the navigational channel as a result of sediment
removal. All of the mobile non-sessile species have the ability to vacate the area during
dredging. Along the channel, where dredging will occur, the removal of the surface sediment
and any associated fauna, will occur over a relatively short time frame.
Once dredging ceases, recovery of the dredged area follows. In a harbour navigation
channel, where both maintenance and capital dredging are routinely carried out, this cycle of
regular disturbance and subsequent recovery has played out as long as the channel has
existed and will continue to do so for as long as the channel is maintained and used. The
benthic environment surrounding the Sligo Harbour navigation channel exists in its current
form after a long history of similar periodic disturbance. The typical phases of recovery
following dredging disturbance are outlined below.
Recovery begins with the colonization of the defaunated area by small opportunistic species
adapted to survive in areas of physical disturbance. This colonization occurs either from
neighbouring sites or via larval settlement or both. Few organisms follow this life style
strategy so there is a tendency for a limited number of species to reach extremely high
densities in the presence of pollutants. The bioturbatory activities of the infauna start to
significantly modify the physical, chemical and biological nature of the deposit. The
macrofaunal assemblage enters a ‘transitory’ phase of succession when the sedimentary
changes allow further colonization of a larger variety of species. This stage is unfavourable
for the ‘pioneer’ population to persist. Species that characterise the transitory sere include
suspension and deposit feeding bivalves, ‘conveyor belt’ polychaetes and relatively immobile
holothurians. Here again the physical and chemical properties of the sediment are further
modified by the new infaunal dominants making way for additional species to take hold. A
more complicated and persistent faunal assemblage now forms and evolves towards an
‘equilibrium’ or ‘climax’ community status.
5-17
Birds
What is described above is typical of recovery from a physical disturbance like dredging.
This recovery sequence is applicable if there is no subsequent disturbance to the site. While
there will be a loss of infaunal habitat due to the removal of sediment from an area of up to
27.2ha, or 0.56% of the overall cSAC area, recolonisation of denuded habitat will occur
quickly and the floral and faunal communities inhabiting the SPA will not be permanently
impacted.
Impacts on benthos from noise in the vicinity of the dredging operation are expected to be
localised and temporary in nature. The fact that the proposed dredging will take place in an
already operational port navigation channel suggests that the additional, temporary noise
loading of a dredger at work would be of minimal significance to the infaunal macrobenthos
in the vicinity of the dredged area.
It is considered that given the factors discussed above, direct impacts on the benthic
environment as a result of the proposed dredging activities will result in a moderate impact in
the short-term in the immediate area. However, the impact will reduce to a slight and then
imperceptible impact within a short period. It is extremely unlikely to have a significant
negative effect on waterbirds within Sligo Harbour/Cummeen Strand, even in the short term.
The dispersion and settlement of sediment released during the dredging works has
the potential to cause impacts directly on the intertidal environment within Sligo
Harbour and as a result, may impact on the macrobenthos. This may have associated
indirect impacts on waterbird species within the SPA which feed on the subtidal
infaunal macrobenthos.
As discussed above, the removal of a small area (up to 27.2ha or 0.56% of the overall cSAC
area) of intertidal material (fine silts and sands) between Ballyweelin Point and the
Deepwater Jetty, within the area delineated by the training walls, will not result in a
significant impact on waterbirds. From observations made during the field surveys, this area
is not of great importance for birds within the estuary as a whole.
5.8.1.1 Potential impacts of sediment dispersion and settlement on the macrobenthos (food
source for waterbirds in Sligo Harbour)
Intertidal macrobenthos is of greatest value to bird species as a food source (due to
accessibility). The subtidal infaunal macrobenthos along the floor of the navigation channel
will be subject to the greatest level of impact (complete removal, though with potential for
rapid recolonisation). Impacts to the intertidal macrobenthos are likely to be imperceptible,
localised and temporary, as the continued movement of the dredger along the navigation
channel will ensure that any given area will not be impacted for a protracted period.
The hydrodynamic modelling presented in Chapter 11 shows that the sediment put into
suspension by the dredger during water injection dredging will be dispersed around the
northern portion of Sligo Harbour. The sediment will be redistributed during periods of
higher current velocities during successive spring tides, before eventually coming to rest in
5-18
Birds
small deposits around the fringes of Sligo Harbour and Cartron Marsh (see Figure 11.8 in
Chapter 11). Some of the material will be successfully transported out of the harbour and
will settle out on the nearby sand banks in depths of a few mm.
During subsequent conventional dredging, small amounts of sediment put in to suspension
by the dredger during dredging operations will be temporarily deposited along the sides of
the navigation channel and in sheltered areas along the north shore of the harbour area.
The areas that will experience the greatest amount of temporary sedimentation occur along
the north shoreline of Sligo Harbour (peak sedimentation during dredging of 20-70mm).
These peak values are typically of a short duration (a matter of hours) and the material may
then be re-suspended and transported elsewhere as the tidal currents pick up during the
subsequent tide. The residual pattern of sedimentation following completion of all
conventional dredging operations is shown in Figure 11.26 in Chapter 11. This shows that
the maximum final deposition depth following completion of operations does not exceed
1mm in the majority of the harbour area and exceeds 25mm only in very localised areas
around the navigation channel and the northern shore of the harbour. Overall, the amount of
sediment deposited in the harbour area as a result of the dredging will be insignificant. No
residual impact is expected.
Potential impacts of sediment dispersion and settlement on seagrass beds (food source for
waterbirds in Sligo Harbour) – background information from Chapter 6 of this report and
Section 6.3.1.3 of the separate Natura Impact Statement for the Cummeen Strand/Drumcliff
Bay SAC.
Marine seagrasses (especially eelgrass, Zostera spp.) are a key food resource for
waterbirds, especially Brent Geese and Wigeon (Mathers et al., 1998). Small areas of this
seagrass occur at the southern edge of Cummeen Strand (Nairn and Robinson, 2003).
Light is one of the key environmental resources imperative for the growth and survival of
seagrasses (Hemminga & Duarte, 2000). The degree of water transparency (which
determines the depth-penetration of photosynthetically active radiation of sunlight) is the
primary factor determining the maximum depth at which seagrasses can occur. Reduction in
light due to turbidity has been identified as a major cause of the loss of seagrasses
worldwide (Shepherd et al., 1989; Green & Short, 2003). The amount of light that reaches a
seagrass leaf is determined by the natural water colour, concentration of suspended solids,
phytoplankton concentration and the epiphyte cover of the leaf. There are various reports of
sublethal and lethal effects on seagrass meadows due to prolonged exposure to high
turbidity and siltation associated with dredging activities (Erftemeijer & Lewis, 2006).
Laboratory experiments have shown that some seagrasses can survive in light intensities
below their minimum requirements for periods ranging from four weeks to several months.
However, widespread seagrass mortality was observed in Chesapeake Bay (USA) following
a month-long (seasonal) pulse of increased turbidity (light extinction coefficient (k)>3.0 m-1)
(Moore et al., 1997).
5-19
Birds
The minimum light requirements of Zostera marina (eelgrass) have been extensively studied
in a range of locations and environments. The values for the minimum light requirements of
this species, as reported in literature, vary between 11 and 37 % of Surface Irradiance (SI).
For the survival of seagrasses, the lowest value of 11%SI is the most critical level below
which widespread mortality surely occurs. Some of the higher values (up to 37%SI) reported
for eelgrass appear to refer to the minimum light levels required to enable and sustain lateral
shoot development, meadow expansion and flowering. Levels below 37%SI but above
11%SI do affect these processes, but may not cause substantial eelgrass mortality. There
has been only 1 detailed study of the minimum light requirements for Zostera noltii: Peralta
et al. (2002) reported a minimum light requirement of 2% of SI for Zostera noltii in Spain.
According to the same study (also reported in: MarLIN Database, 2006), Zostera noltii plants
can tolerate acute light reduction below 2% SI for up to two weeks, and thus appear tolerant
of short-term events of very high turbidity. A recent monitoring study into the effects of a
dredging plume on intertidal eelgrass (Zostera marina) in the Ems Estuary (The
Netherlands) during (day-time) periods of low tide exposure (Ochieng & Erftemeijer, 2009).
This implies that intertidal eelgrass plants are relatively tolerant to further turbidity increases
such as may be caused by a dredging plume (Ochieng and Erftemeijer, 2009). Based on the
above information, the tolerance thresholds of seagrass beds to turbidity is summarised in
Table 5.4.
Table 5.4: Tolerance thresholds of Zostera spp. to turbidity levels.
Seagrass
Species
Zostera marina
Zostera noltii
Minimum Tolerated
11-37% SI
2% SI can tolerate acute
light reduction below 2%
SI for 2 weeks
Optimum
Range
>37% SI
Several studies have documented deterioration of seagrass meadows by smothering due to
excessive sedimentation (Erftemeijer and Lewis, 2006). Seagrass species that develop
vertical shoots may respond to fluctuations in sediment depth by modifying their vertical
growth but there are limits to the level of sedimentation seagrasses can tolerate.
Sedimentation rates of as much as 1013 cm yr-1 have been reported as maximum threshold
of what some seagrass species can survive. Settlement of suspended material on leaf
blades of seagrasses may interfere significantly with photosynthesis, and appears especially
significant in low wave energy environments where fine sediments are present and can
settle out. A maximum allowable sedimentation rate of 2 cm in 4 months was reported for
Mediterranean Zostera noltii (Spain). Tolerance of Zostera noltii in the Dutch Wadden Sea
was documented to range from minor erosion of 2 cmyr-1 to maximum sedimentation levels
of 25 cm yr-1. Mortality of 75% was reported for Zostera marina meadows (USA) at burial
with 4 cm (i.e. 25% of plant height), which demonstrates that this species is probably more
sensitive to sedimentation than some of the other (taller) seagrass species. Vermaat et al.
(1997) proposed an estimate of the annual sedimentation rates that can be survived or
escaped by seagrasses, either vertically or horizontally, to be in the order of 5-10 cm yr-1.
5-20
Birds
Based on the above information, the tolerance thresholds of seagrass beds to sedimentation
is summarised in Table 5.5.
Table 5.5: Tolerance thresholds for Zostera spp. to sedimentation.
Seagrass
Minimum Tolerated
Maximum Tolerated
Species
Zostera marina
75%
mortality
at
4cm/day (25% of plant
height
Zostera noltii
-1 to -2 cm/yr (erosion)
2-5 cm/year
(sedimentation)
2cm / 4 months
Impacts of the dredging plume on the seagrass beds in Sligo Harbour are considered to be
imperceptible; because the plumes of high turbidity and sedimentation do not reach the
seagrass beds documented in the area (they are remote from the shipping channel and
occur at the southern edge of Cummeen Strand). Intertidal seagrass is also likely to be
unaffected by increased turbidity, since it obtains most of its light during (day-time) periods of
low tide exposure (see Ochieng & Erftemeijer, 2009). Based on the final sediment deposition
depth computed for the Cummeen Strand seagrass habitat, on completion of all dredging
activities, no residual impact on this habitat is expected.
5.8.1.2 Indirect impacts on bird species
As discussed above, significant deposition will only occur in small sheltered areas along the
coastline, particularly along the north shoreline (refer to Figures 11.7 and 11.8 as well as
11.24, 11.25 an 11.26 of Chapter 11, Coastal Processes). Overall the amount of sediment
deposition in the harbour area on completion of dredging is expected to be relatively small
as both the deposition depths and the increase in the level of the suspended sediment
concentrations in the greater part of the harbour area are not considered to be significant. As
such, the dispersion and settlement of sediment released during the dredging works will
have an imperceptible impact on waterbirds within Sligo Harbour/Cummeen Strand.
The disposal of the dredged material has the potential to impact on the intertidal
environment (habitats and fauna) within Sligo Harbour.
It is proposed to dispose of all of the dredged material at an offshore dumpsite (see Chapter
4, Project Description and Figure 4.2). The proposed dump site (subject to granting of a
licence by the EPA) is located some 34 nautical miles (63km) from the deepwater jetty at
Sligo, in waters that are 92 – 93m in depth. This element of the dredging works does not
pose any risk of negative impacts to either the habitats or fauna of Sligo Harbour/Cummeen
Strand.
5-21
5.9
Birds
MITIGATION MEASURES
5.9.1 Mitigation by Reduction/Remedy
As the proposed dredging activities do not pose a risk of significant negative effects on
waterbirds in Sligo Harbour/Cummeen Strand as a result of disturbance, no mitigation
measures will be necessary.
As the physical act of dredging does not pose a risk of significant negative effects on
waterbirds in Sligo Harbour/Cummeen Strand as a result of the removal of intertidal and subtidal material from the estuary, and the associated impacts on the benthic environment
(either directly to the infaunal macrobenthos, or indirectly on the tidal regime of the estuary),
no mitigation measures will be necessary.
The dispersion and settlement of sediment released during the dredging works does not
pose a risk of significant negative effects on waterbirds in Sligo Harbour/Cummeen Strand,
either through direct or indirect impacts. As a result no mitigation measures will be
necessary.
5.10
RESIDUAL IMPACTS
As discussed under Section 5.8 above, none of the predicted impacts of the proposed
capital and maintenance dredging in Sligo Harbour will result in significant negative effects
on waterbirds. This is also discussed in detail in the Screening for Appropriate Assessment
Report, the conclusions of which are provided below (for full Screening for Appropriate
Assessment Report, refer to Appendix 3B). There are no residual impacts of the proposed
capital and maintenance dredging works on waterbirds within Sligo Harbour.
5-22
6.0
Intertidal and Benthic Flora and Fauna & Marine Mammals
INTERTIDAL AND SUBTIDAL FLORA AND FAUNA, MARINE
MAMMALS
This chapter provides an assessment of the likely impact on the marine ecological
environment by the proposed dredging in Sligo Harbour and associated dumping at sea.
The assessment focuses on ecological features of conservation significance and specific
methodologies used for the individual sub-sections of this Chapter are provided below.
6.1
INTRODUCTION
The principal focus of the impact assessment will be to consider the potential impacts of the
dredging within Sligo Harbour itself, as the site holds SAC and SPA designations. A
programme of marine intertidal and subtidal ecological surveys was drawn up, centred on
the navigation channel but extending throughout Sligo Harbour and into Sligo Bay. These
studies and the associated impact assessment are presented in section 6.2 of this chapter.
Further benthic studies have been undertaken at the proposed dump site, some 34 nautical
miles west of the harbour quays. These studies included current meter recording (including
deployment of drogues, ROV acquisition and benthic grabs. The results of these surveys
and the associated impact assessment are presented in section 6.3 of this chapter.
A marine mammal survey covering Sligo Harbour and the surrounding waters in Sligo
Bay/Dumcliff Bay has also been undertaken, incorporating a desktop assessment, field
surveys and impact assessment. These surveys are presented in Section 6.4 of this
chapter.
The proposed dredging area lies within the Cummeen Strand/Drumcliff Bay (Sligo Bay)
Shore SAC, which forms part of the Natura 2000 site network established under the EC
‘Habitats’ Directive (92/43/EEC). The European Communities (Natural Habitats) Regulations
1997 (SI 94/1997) transpose the Habitats Directive into Irish Law. Under this legislation the
proposed dredging requires an appropriate assessment under Article 6(3) and 6(4) of the
Habitats Directive. Under Part IV of the Habitat Regulations, Planning and Development
Matters, an EIA can be considered as an appropriate assessment. Notwithstanding this, the
EC guidance states that the assessments required under Article 6 should be clearly
distinguishable and identified within the Environmental Appraisal or reported separately.
Therefore Sections 6.2 to 6.4 of this Chapter will discuss the individual impact assessments
undertaken for the Environmental Appraisal whilst the Natura Impact Statement to support
the Appropriate Assessment Process is presented separately in Volume 3 of this Report.
IBE00440/EIS01/June ‘12
6-1
6.2
INTERTIDAL AND SUBTIDAL FLORA & FAUNA – DREDGING AREA
6.2.1 Introduction
6.2.1.1 Project background
Aquafact International Ltd were commissioned to describe the intertidal and subtidal flora
and fauna that exist in Sligo Harbour and evaluate the potential impact of the proposed work
on the habitats and species present. An A3 figure showing the extents of the proposed
dredging area is presented in Figure 4.1 (page 4-3) in Chapter 4 of this Environmental
Appraisal.
6.2.1.2 Sligo Harbour
Sligo Harbour is a large embayment located between Sligo City to the east and Rosses
Point village to the west. It measures approximately 6 km in length (from West to East) and
is approximately 3 km wide at its widest point. The Garavogue River discharges through
Sligo Harbour and the main channel runs along the northern edge of the embayment.
Extensive sand flats are present throughout the area, with large sand flats to the south of the
embayment at Cummeen Strand and Dorrins Strand. Several mussel banks are present
throughout these flats, in addition to commercial clam farming being undertaken close to the
main channel at Cummeen Strand.
6.2.2 Desktop Study
6.2.2.1 Intertidal habitats
The Aquatic Services Unit (ASU) of University College Cork (UCC) has carried out several
intertidal studies in the Sligo Bay area and within Sligo Harbour. Recent intertidal work
carried out by ASU in the Sligo Harbour area includes:
x
A survey covering a small area in the south west corner of Dorrins Strand, 2005
(carried out as part of an EIS for a proposed extension of the Sligo airport site). 12
stations were sampled in a relatively small study area. Samples taken included faunal
cores (x3) and samples for granulometric and organic carbon analysis.
x
An assessment of the wider intertidal benthic community of Sligo Harbour, 2007
(carried out as part of an EIS for a proposed extension of the Sligo airport site). 30
stations were sampled over a large area of Sligo Harbour. The sampling regime
included faunal cores (x5), 1 x 1m2 quadrat described physically and biologically, 1 x
0.25m2 quadrat was marked out and excavated to a depth of 20cm. Sediment was
sieved in situ through a 5mm mesh sieve. Samples were taken for granulometric and
organic carbon analysis.
x
A survey of Mudflats and Sandflats in Ireland, 2007 (commissioned by the National
Parks and Wildlife Service). This survey consisted of several shore transects in the
Sligo Bay area. Three stations were investigated on each transect – a High, Mid and
Low shore station. At each of these stations, faunal cores (x5), a 1 x 1m quadrat was
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excavated using a hand spade to a depth of 20cm and examined for macrofaunal
content. A core was also taken for granulometric and organic carbon analysis.
6.2.2.1.1
Aquatic Services Unit, UCC – Dorrins Strand 2005
(Excerpt from ASU, 2005). The area of Sligo Bay surveyed at Dorrins Strand was
dominated by an expansive sandy intertidal area ringed for the most part by a narrow
saltmarsh fringe. This site was just to the east of Sligo Airport runway. Immediately below
the saltmarsh fringe the shore was mainly comprised of sand right from the top of the shore.
This was supplemented just east from where Sligo Airport runway comes closest to the
shore around to Rinn Point by a narrow upper shore gravel / cobble fringe interspersed with
muddy sand in places. This latter was dominated by the brown seaweed, spiral wrack
(Fucus spiralis) with a locally heavy cover of the green seaweed, Enteromorpha sp.,
especially common close to where a small freshwater stream flows onto the shore running
east. The stream joins the shore immediately east of where the small by-road (from the
south) reaches the shore. At low tide, the small stream hugs the shore travelling east to
ENE in a shallow channel on the surface of the sand, eventually joining the main eastwest
tidal channel just off Rinn Point. The intertidal channel of the stream near where it joins the
east-west tidal channel and the tidal channel itself, had significant numbers of loosely
scattered clumps of Enteromorpha and to a lesser extent small clumps of filamentous brown
and red algae (e.g. Ceramium nodulosum). In addition, numerous small gobies were visible
in the shallow water of these channels during low water.
A couple of smaller
streams/drainage ditches drain to the shore closer to the airport runway and these join the
main tidal channel via short shallow meandering channels.
The sandy or muddy sand habitats of the shore appear (in May) rather uniform to the eye
with virtually no macroalgal (large seaweed) cover. The most obvious feature is the
moderately dense lugworm (Arenicola marina) burrows which dominate most of the shore,
particularly south of the east-west running low-tide channel. North of this channel the shore
height is slightly higher, and the substrate slightly drier and sandier and so the lugworm
densities are visibly lower. Around all the lower-lying and wetter areas of the flats e.g.
stream channel edges, the lugworm cast density tends to be highest. During early August
much of the soft-sediment intertidal area about 70m to the south of the east-west flowing
tidal channel had a moderate to locally dense cover of the green filamentous alga Vaucheria
sp.
The only area where there is a typical rocky shore community was on the short steep rockarmoured shore, which begins adjacent to the eastern end of the runway and runs north east
along the shore for a short distance. This is a typical sheltered shore dominated by brown
fucoid seaweeds. The upper shore boulders were virtually devoid of the yellow and grey
lichen zones, which are sometimes evident on such substrates and the brown seaweed
channel wrack is confined to a few scattered clumps at the top of the shore. This was
followed by a better-defined, but narrow (~0.5m), band of Fucus spiralis and then by the
main zone which is dominated by two more brown seaweeds: egg wrack (Ascophyllum
nodosum) and bladder wrack (Fucus vesiculosus) forming a dense band of about 3m width
and 100% cover. The lower shore and shallow subtidal were dominated by Fucus serratus
(serrated wrack), Laminaria saccharina (strap weed or sugar wrack) and clumps of the
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invasive brown seaweed Sarragassum muticum. Bootlace weed (Chorda filum) was present
in the deeper (>1m) water of the sandy-bottomed channel adjoining the shore at this point.
Most of the mid to lower shore brown algae had other finer seaweed growing as epiphytes
on them including fine filamentous browns and fine red algae such as Polysiphonia lanosa,
Aglaothamnion roseum and Ceramium pallidum. Other, very infrequent small reds included
Hypoglossum hypoglossoides and Apoglossum ruscifolium on silted rock in the lower shore.
Some Enteromorpha was also present on this shore.
The intertidal fauna was quite sparse and comprised scattered littorinid snails (including the
edible periwinkle Littorina littorea and L. obtusata/mariae), frequent limpets (Patella vulgata),
occasional dog whelks (Nucella lapilis), blue mussels (Mytilus edulis) and top shells (Gibbula
cineraria). Barnacles were not common on the shore and included Semibalanus balanoides
and Elminius modestus. The shore crab (Carcinus maenas) was also occasionally noted
under stones. The lower boulders on the shore had coatings of silty sand on their surfaces.
Small hydroids (Dynamena sp.) were noted as epizootic on fucoid algae, as was the
Bryozoan Alcyonidium sp. The fine sponge Leucsolenia sp. was noted under stones in the
mid-lower shore, while another sponge, Hymeniacidon perleve was occasionally found on
the sides of silted boulders in the same locations. In the upper sub-tidal large clumps of the
sea squirt (Tunicata) Ciona intestinalis (deep orange form) was present on brown algal
covered boulders.
6.2.2.1.2
Aquatic Services Unit, UCC – Wider Sligo Harbour Intertidal Survey 2007
An assessment of the wider intertidal benthic community of Sligo Harbour, 2007 (carried out
as part of an EIS for a proposed extension of the Sligo airport site). 30 stations were
sampled over a large area of Sligo Harbour. The sampling regime included faunal cores (x5),
1 x 1m² quadrat described physically and biologically, 1 x 0.25m² quadrat was marked out
and excavated to a depth of 20cm. Sediment was sieved in situ through a 5mm mesh sieve.
Samples were taken for granulometric and organic carbon analysis.
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Figure 6.1: Map showing the location of the 30 intertidal stations surveyed by ASU in
2007.
6.2.2.1.3
Aquatic Services Unit, UCC - Intertidal Transect Survey 2007
The following section is taken from Aquatic Services Unit (2007). Aquatic Services Unit,
University College Cork, was employed by the Department of Environment, Heritage and
Local Government National Parks and Wildlife Service to carry out a survey of mudflats and
sandflats across seven intertidal SACs (Special Areas of Conservation) around Ireland. As
part of this survey, ASU undertook a detailed survey of intertidal habitats in Sligo Harbour –
three transects were surveyed in Sligo Harbour itself. An additional four transects were
surveyed in the adjoining SAC of Ballysodare Bay.
x
Sligo Harbour Transect 1
Transect 1 (length 1930m) was located along the southern shore of Sligo Harbour. The
shore was backed by a 2 – 3 meter high sea all, which connected directly to the main
road. The upper section of the wall was characterised by the presence of lichens. At the
base of the wall was a band of Enteromorpha ulva. This immediately gave way to a
band of Fucus sp. attached to cobble within a sediment matrix. There was evidence of
freshwater influence across the area, as a drain was present 10 metres from the start of
the transect. The transect crossed a shallow channel approximately thirty metres from
the start of the transect. The upper shore site was located within the intertidal from the
sea wall to the shallow channel. The transect crossed an extensive mussel bank, which
ran in a west-northwest direction across Cummeen Strand.
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This raised bank of mussels measured approximately 35 to 40m across at this point of
the transect. The mid shore area of the transect was characterised by the presence of a
significant amount of standing water (ranging from 50% to nearly 100% in places).
Arenicola sp. casts were abundant at this shore height. A clam farm was present
approximately 1½ km along he transect, and there was evidence of motorised vehicle
use on the sediment. The low water site was taken immediately adjacent to the main
channel. The strandline at Transect 1 returned 25 specimens of a single species,
Orchestia gammarellus.
Figure 6.2: Figure showing location of transects surveyed by ASU in Sligo Bay, 2007.
x
20m from the shoreline – T1 high shore station
The sediment at this shore height has been classified as gravelly sand, with a significant
amount of mud present. Standing water was evident at the site, covering 25% of the
sediment surface. An anoxic layer was present just beneath the sediment surface, with
evidence of a stone layer at a depth of 10cm. The station was located approximately 20
meters from a shallow channel which crossed the transect at the upper shore level.
Macoma balthica shells were present on the sediment surface, and live specimens were
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recovered in the dig. Enteromorpha intestinalis and Fucus vesiculosus were present on
the sediment surface. No Arenicola sp. casts were present within this shore height,
although a single specimen was recovered in the 1m dig.
x
900m from the shoreline – T1, mid-shore station
This sediment at this station was dominated by fine rippled sand. The anoxic layer was
present at a depth of 2 cm, and presented as a black layer. A thick shell layer was
present at a depth of 15cm. The sediment was under a significant amount of standing
water (~85%). Fifteen Arenicola sp. casts were identified in the quadrat, although only
two specimens were returned in the dig. In addition, large numbers of dead cockle
shells were present on the sediment surface. Enteromorpha intestinalis and Fucus
vesiculosus were present on the sediment surface. The station was located
approximately 100m from the raised mussel bank.
x
1950m from the shoreline – T1, low shore station
This station was taken immediately adjacent to the main channel at low water. Sediment
at this site was characterised as rippled gravelly sand. There was no visible fauna
present on the sediment surface, although the red algae Ceramium sp. was present.
The depth of the anoxic layer at this site was 10cm. Approximately 30% of this site was
under standing water, which was present between the ripples.
x
Transect 2 (length 1990m) was located along the southern shore of Sligo Harbour
running from the shoreline near Coney Island causeway in a north-northwest direction
to the lighthouse on Oyster Island. The shore was backed by a narrow strip of saltmarsh
and agrcultural land giving way to fine rippled sand with a layer of water over it. This
gave way to an extensive area of rippled sand with extensive amounts of Cerastoderma
edule and Arenicola marina casts on the sediment surface. At the low water site Lanice
conchilega dominated. C. edule were also evident at low water.
The strandline at Transect 2 returned 9 specimens of Orchestia meditteranea and 5
specimens of Ligia oceanica.
x
185m from the shoreline – T2, upper shore station
The sediment at this station was dominated by fine sand. The site was located in a
water channel, with a very weak flow (100% cover). Dead cockle shells were present on
the sediment surface. Arenicola casts were present on the sediment surface (3 per
square meter) and 1 was returned in the dig. There was occasional Enteromorpha
present at this shore height.
x
The sediment at this station was characterised as rippled muddy sand. The anoxic layer
was present at 4cm depth. There was a significant amount of standing water present
within this area, with ~75% of the sediment covered with a thin layer of standing water.
There were significant numbers of Cerastoderma edule on the sediment surface.
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Arenicola casts were present (2 per square meter) although none were returned in the
dig. There were occasional clumps of Enteromorpha present at this shore height.
x
1990m from the shoreline – T2, low shore station
This station was taken immediately adjacent to the main channel at low water. Sediment
at this site was characterised as rippled fine sand. The anoxic layer at this site was
15cm deep. Standing water (10%) was present between the ripples on the sediment
surface. Lanice conchilega and Cerastoderma edule were abundant and algae were
present in significant numbers on the sediment surface (Enteromorpha and Ceramium).
x
Transect 3 (length 135m) was located along the outer part of Sligo Harbour between the
mainland, near Sligo Airport and Coney Island. There was a channel running between
Coney Island and the mainland. The shore was backed by a dune system, giving way to
a cobble/boulder with a large amount of algal drift at the uppermost part of this. This
leads to a soft mobile sand area with occasional clumps of Fucus vesiculosus and
Fucus serratus. At 50 meters this sand becomes more firm. Arenicola casts were
present from this location to the low water site. At 60 meters, the sediment becomes
wet, and Enteromorpha became more abundant. The bottom of the transect is
characterised by shell and sand with large numbers of Enteromorpha. On both sides of
this transect, the shoreline was dominated by a fucoid covered boulder shore, with
limited soft sediment in evidence.
The strandline at transect 3 returned 94 specimens of a single species, Orchestia
gammarellus.
x
20m from the shoreline – T3, upper shore station
The sediment at this station was characterised as rippled gravelly sand. The sediment
was very dry and there was no evidence of fauna on the sediment surface. The anoxic
layer was not visible at this site.
x
The sediment at this station was dominated by wet sand. The anoxic layer was present
just beneath the sediment surface. Enteromorpha was present on the sediment surface
with occasional clumps of Fucus present along the shore height. Arenicola casts were
present at this shore height (6 per square meter), although only 1 specimen was
returned in the dig.
x
130m from the shoreline – T3, lower shore station
This station as taken immediately adjacent to the main channel at low water. Sediment
at this site was characterised as gravelly sand. The anoxic layer was present just below
the sediment surface. The sediment surface was dominated by the fucoid algae Fucus
serratus, F. vesiculosus, with Enteromorpha present in significant numbers. Arenicola
casts were present (1 per square metre) and a single specimen was returned in the dig.
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6.2.2.1.4
BIOMAR and Office of Public Works intertidal surveys
A number of intertidal areas were surveyed by the BIOMAR team and Office of Public Works
in 1996 (Picton & Costelloe, 1998). These are shown in Figure 6.3. (Site two was a subtidal
station surveyed using SCUBA equipment off Ballyconnell Point, South Donegal Bay). The
data collected at these stations give a good indication of the variation of floral and faunal
communities to be found along this stretch of coast. Sites were surveyed in detail with
substrates, site exposures, habitats, biotopes and species present and abundance scales all
recorded. Sediment cores were taken at several of the sites where sedimentary habitats
dominated. (Detailed data for each of these stations are presented in Appendix 4A of the
Environmental Appraisal).
Figure 6.3: Location map for the sites surveyed by BIOMAR and OPW teams in Sligo
Bay 1996.
Sites 6, 7 and 8 are in closest proximity to the dredging work proposed for Sligo Harbour.
Site 6 was located in an exposed area at Rosses Point on the western edge of the small
peninsula separating Sligo Harbour from Drumcliff Bay. This is a gently sloping beach
composed of fine, well-sorted sand backed by low dunes with little surface evidence of life.
Sampling showed the presence of polychaetes (Angulus tenuis) and bivalves (juvenile
Donax sp.). Brown shrimp (Crangon sp.) were present in a midshore runnel.
Site 7 was located in a very sheltered area at Dorrins Strand on the south shore of Sligo
Harbour. It ran from the southern end of the roadway to Coney Island across the large sand
flat to the edge of the main channel to the south of Oyster Island (approximately 2km). The
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shore was backed by grassland and a narrow strip of salt marsh giving way to rippled fine
sand with a shallow layer of standing water. A wide (100m) shallow channel (2-5cm), split by
a sandbar, was located approximately 100m from the shore. The bed of the channel was soft
rippled sand with frequent cockles, Arenicola sp. casts and frequent clumps of
Enteromorpha sp. on the surface. To the north of this channel the sand was firmand, for the
most part, covered with a layer of standing water and had an anaerobic layer 1-2cm below
the surface. A. marina castings were visible on the surface at densities of 1-9 per metre
squared with Cerastoderma edule present in the top 10-15 cm of sediment at densities of 15 per metre squared. Fine tube worms were also common. At 1.75km out from the shore the
surface rose gently to the top of a large sandbank running adjacent to the main channel. The
sediment on the bank was coarse and dry with an ARPD layer greater than 25cm below the
surface. At 2km out from the shore the sandbank sloped down to the main channel with a
dense bed of Lanice conchilega and filamentous brown algae 50m from the channel. Ulva
sp. was also present attached to worm tubes with an anoxic layer 10cm below the sediment
surface in the coarse sand and broken shell at the channel edge.
Site 8 was located at Cummeen Strand in Sligo Harbour. It was taken from the sea wall next
to Gibraltar Point on the southern shore to the main channel on the north side of the bay.
This transect was approximately 2km long and crossed a small channel about 50m from the
sea wall. It started with an area of mud, gravel and stone sloping gently to the shallow
channel and was characterised by Enteromorpha spp., Ulva sp., Fucus ceranoides and
Scrobicularia plana. Beyond the channel the beach had a short steep upward slope
characterised by small burrows containing very small gastropods. The beach appeared flat
for 600m and was characterised by Arenicola marina for the first 300m and then by a mixture
of A. marina for the first 300m and then by a mixture of A. marina and Cerastoderma edule.
Between 600m and 700m there was a dense mussel bed with mussel and dead cockle
shells banded together on the shoreward side. Some F. vesiculosus and Enteromorpha sp.
were present on the bed. Seaward of this the shore sloped very gently to the channel and
was covered with standing water 1.5cm deep with small cockles present for the next 200m.
After this, cockles were occasional as were A. marina casts. The sand was very flat with
small tubes present. Close to the channel the sand became rippled and algae (in particular
Polysiphonia sp. or Ceramium sp.) were attached to dead cockle shells. Close to the
channel the sand became rippled and algae, in particular Polysiphonia sp. or Ceramium sp.
were attached to dead cockle shells. Lanice conchilega were frequent sat the channel edge.
Across most of the beach Enteromorpha spp. were present attached to dead shells. The
anoxic layer varied from 1 to 10cm below the sediment surface but was generally 1cm to
5cm beneath the surface. Clam beds were present on the beach.
6.2.2.2 Subtidal habitats
6.2.2.2.1
BIOMAR and Office of Public Works subtidal surveys
A single subtidal station in close proximity to the proposed work was surveyed by the
BIOMAR team in 1996. This site was located off Ballyconnell Point and was adjacent to the
very exposed headland near the entrance to inner Sligo Bay. The dive documented a large
subtidal cliff with abundant jewel anemones (Corynactis viridis). This stretched from 13m to
approximately 26m BCD. Stepped limestone bedrock was documented at the bottom of the
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cliff with Devonshire cup-corals (Caryophyllia smithii) and jewel anemones (Corynactis
viridis). This type of subtidal environment is typical of the more exposed, outer areas of Sligo
Harbour. The inner harbour (east of Coney Island) is typically characterised by sedimentary
habitats. This includes the deepened approach channel for the harbour.
Subtidal habitat in Sligo Harbour is very limited in areal extent when compared with intertidal
habitat and is largely confined to the deeper channels present – the primary areas being the
navigation approach channel along the northern shore of the harbour and the channel
surrounding Oyster Island.
6.2.3 Field Survey – Aquafact 2010
Numerous intertidal surveys have been carried out in Sligo Harbour in recent years (see
section 6.2.2.1). Field surveys were undertaken in Sligo Harbour by Aquafact in 2010
specifically for the proposed dredging scheme.
The objective of the intertidal survey was to carry out:
x
A general walkover of the harbour, incorporating:
The shore of the navigation channel
areas of mussel bank
clam production areas
areas of Zostera bed.
x
In addition to:
Documenting existing habitats along the route with notes and photographs.
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Figure 6.4: Map showing recent intertidal survey effort, Sligo Harbour.
(The route of the current intertidal walkover is shown in red. Survey stations & transects
carried out by ASU in 2005 and 2007 are also shown. Orthorectified images © OSI
Figure 6.5: Location of observations made during the walkover survey, October 2010.
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6.2.3.1 Materials and Methods - 2010
The survey was carried out on 7th- 8th October, 2010. Cloud cover varied between 3/8ths and
7/8ths. The southern shore was accessed at the Scarden More landfall of the Coney Island
causeway. A four wheel drive vehicle was used to transit the shore during the work. A
Trimble® GeoXT™ handheld mapping unit was used to record the track followed during the
survey work and to document various features encountered. This unit provides real time submetre accuracy. Digital photographs were taken during the survey. The camera time was
synchronised with UTC to allow matching of images to their locations.
Bird species present on the shore were noted during the survey. Photographs and notes
were taken throughout the survey work.
6.2.3.2 Results 2010
6.2.3.2.1
Anthony Lynch - Clam site - Northern Walkover
This survey covered the area shown in Figure 6.5. Notes and photographs were taken
during the walkover along with GPS coordinates at features of interest. For the most part the
shoreline was characterised by the presence of clean fine-medium sand with a variable shell
fraction.
The following sections (denoted by letters A-N) correspond with each point marked by the
letters shown in Figure 6.5 showing the intertidal location of documented observations.
A. The beach here was composed of fine sand. Numerous wheeled clam trestles were
noted. Small stands of algae (primarily Enteromorpha sp.) were recorded attached to
larger shell fragments on the shore. Small amounts of fucoid algae (Fucus
vesiculosus) were found attached to the trolleys themselves.
Figure 6.6: Trestles, clam farm site, Sligo Harbour, 07th October 2010.
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Figure 6.7: Commercial clam park. South west Sligo Harbour, 07th October 2010.
B. Mussel bank 1. This area was characterised by a mussel bed. There was a mix of
blue mussel and clams. Algal cover was noted around the margins of the bed.
Figure 6.8: Mussel bed, Sligo beach, 07th October 2010.
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Figure 6.9: Mussel bed, close view. A mix of blue mussel and clams.
Figure 6.10: Algae (primarily fucoids) on mussel bank, Sligo Harbour, October 2010.
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Figure 6.11: Lugworm feeding casts, near mussel bank, Sligo harbour, October 2010.
C. Seagrass bed. A seagrass bed was noted here. Some algal cover (primarily
Enteromorpha sp.) and lugworm casts (Arenicola sp). were noted.
Figure 6.12: Seagrass and lugworm feeding casts, Sligo Harbour, October 2010.
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D. Filamentous algal mat over muddy sand flat. The intertidal was quite soft in this area.
An extensive mat of filamentous algae was noted (primarily Vaucheria sp.). A shallow
tidal channel ran through this area.
Figure 6.13: Vaucheria sp. mat over intertidal muddy fine sand flat, Sligo Harbour, 07th
October 2010.
E. Geese feeding on intertidal flat. A flock of gooses was noted feeding in the intertidal
zone. As well as supporting a seagrass bed of variable density this area had quite a
high density of lugworm feeding casts.
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Figure 6.14: Gooses feeding on the intertidal sand flat, 07th October 2010.
F. Fyke net on pole in shallow tidal channel. A single fyke net on a pole was noted at
the centre of a shallow tidal channel in the sand.
Figure 6.15: Fyke net on pole, Sligo Harbour, 07th October 2010
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G. Mussel bank 2. Another dense area of mussel bed was recorded in this area.
Figure 6.16: Mussel bank, Sligo Harbour, 07th October 2010.
H. Mussel bank 3. A third extensive area of mussel bank was recorded.
Figure 6.17: Mussel bank Sligo Harbour, 07th October 2010.
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I.
Commercial clam park (Noel Carter’s). Clam cultivation frames and plots in clean,
rippled fine sands. Some algae were present – Enteromorpha sp. attached to larger
shell fragments etc. on the sand flat, and fucoids on any available hard surfaces
(clam cultivation hardware for example).
Figure 6.18: Commercial clam park (Noel Carter’s). Sligo Harbour, 07th October 2010
Figure 6.19: Clam cultivation hardware, Sligo Harbour, 07th October 2010.
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Figure 6.20: Rippled fine sand surrounding clam cultivation site, 07th October 2010.
J. Intertidal sands with filamentous algal growth.
Figure 6.21: Intertidal area with filamentous algal growth, Sligo Harbour, October 2010
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6.2.3.2.2
Sligo Intertidal – Navigation Channel Area
A walkover survey was conducted in the intertidal zone to the north of the navigation channel
in Sligo Harbour at low water on 8th October 2010. This survey covered the area shown in
Figure 6.22. Notes and photographs were taken during the walkover along with GPS
coordinates at features of interest.
Orthophotography © Ordnance Survey Ireland. All rights reserved. Licence number 2010/20 CCMA/ Sligo County Council
Figure 6.22: Points of interest near the navigation channel walkover area 7th October
2010.
The following sections (denoted by letters K-N) correspond with each point marked by the
letters shown in Figure 6.22 showing the intertidal location of each documented observation.
K. Intertidal sand flat with sparse algal cover. The sediment surface here was composed
of quite firm, rippled fine sand. Occasional fragments of shell gravel were noted.
Sparse algal cover (mostly Enteromorpha sp.) was recorded.
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Figure 6.23: Rippled fine sand with some algae, 08th October 2010.
Figure 6.24: Channel marker, Sligo harbour, 08th October 2010.
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Figure 6.25: Base of channel marker & training wall, Sligo harbour, 08th October 2010.
L. Clean rippled sand flat. An area of clean, rippled, tide-swept fine sands.
Figure 6.26: Intertidal sand flat, Sligo Harbour, 08th October 2010.
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M. View along navigation channel towards Sligo.
Figure 6.27: View towards Sligo along navigation channel, 08th October 2010.
N. A close up view of the harbour training wall. Species recorded included algae
(primarily Fucus vesiculosus), barnacles (Semibalanus balanoides), limpets (Patella
vulgata) and mussels (Mytilus edulis). The intertidal flat at the base of this wall sloped
very gently towards the navigation channel. The sediments here were composed of
muddy fine sand. Small, low ridges of stabilised sediment supporting filamentous
algal growth were noted. Numerous lugworm (Arenicola sp.) feeding casts were
noted.
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Figure 6.28: Encrusting flora and fauna on the northern Sligo harbour navigation
channel training wall, Sligo Harbour, 08th October 2010.
Figure 6.29: Muddy sand flat adjacent to training wall, Sligo harbour approach
channel, 08th October 2010.
6-26
6.2.3.3 Infaunal survey – Marine benthos 2010
6.2.3.3.1
Sampling Procedure & Processing
To carry out the infaunal survey of Sligo Harbour, Aquafact sampled a total of 15 stations.
These stations can be seen in Figure 6.30. Table 6.1 shows the station coordinates.
Sampling was carried out on the 6th and 7th October 2010 from Aquafact’s RIB. Stations
were located using DGPS and this positioning method is accurate to within ca. 1m. A
0.025m2 grab sampler was used to collect the benthic samples. Three replicate samples
were taken at each of the 15 stations. Data on each sample, e.g. station number, date, time,
depth of sediment, surface features and visible macrofauna were logged in a field notebook.
The faunal returns were sieved on a 1mm mesh sieve, stained with Rhodamine dye, fixed
with 10% buffered formalin and preserved in 70% alcohol. Samples were then sorted under
a microscope (x 10 magnification), into four main groups: Polychaeta, Mollusca, Crustacea
and others. The ‘others’ group consisted of echinoderms, nematodes, nemerteans,
cnidarians and other lesser phyla. The taxa were then identified to species level where
possible.
An additional sample was taken at Stations 1 to 14 for sediment granulometric analysis. The
sediment samples were taken through the opening on the top of the grab. Samples were
also taken for determination of total organic carbon content. All samples were stored
immediately in a cold room on board the vessel and were frozen at –20oC on return to the
lab.
Particle size analysis was carried out using the traditional granulometric approach.
Traditional analysis involved the dry sieving of approximately 100g of sediment using a
series of Wentworth graded sieves. The process involved the separation of the sediment
fractions by passing them through a series of sieves. Each sieve retained a fraction of the
sediment, which were later weighed and a percentage of the total was calculated.
Table 6.2 shows the classification of sediment particle size ranges into size classes. Sieves,
which corresponded to the range of particle sizes, were used in the analysis.
6-27
Extract from Admiralty Chart 2852 © Crown Copyright UKHO. Not for navigational use
Figure 6.30: Map showing subtidal sampling locations
Table 6.1: Subtidal station co-ordinates.
Station
Easting
Northing
Longitude
Latitude
1
163931.8
339745
-8.55414
54.3051
2
165748.2
339095
-8.52616
54.2994
3
167086.5
338473.6
-8.50553
54.2939
4
160270.5
341198.1
-8.61058
54.3179
5
165729
339486.9
-8.5265
54.3029
6
168453.5
337536.8
-8.48444
54.2856
7
162115.5
338540.5
-8.58189
54.2942
8
164677.5
339286.2
-8.54263
54.301
9
166369.5
339066.3
-8.51661
54.2992
10
167392.4
338339.8
-8.50082
54.2927
11
167946.9
337374.3
-8.4922
54.2841
12
165662.1
337278.7
-8.52727
54.2831
13
166057.4
338759.7
-8.52137
54.2964
14
165018.3
338818.4
-8.53734
54.2969
15
159843.2
340666.7
-8.61707
54.3131
6-28
Table 6.2: The classification of sediment particle size ranges into size classes
Range of Particle Size Classification
<63µm
Silt/Clay
63-125 µm
Very Fine Sand
125-250 µm
Fine Sand
250-500 µm
Medium Sand
500-1000 µm
Coarse Sand
1000-2000 µm
Very Coarse Sand
>2000 µm
Gravel
(adapted from Buchanan, 1984)
6.2.3.3.2
Phi Unit
>4 Ø
4 Ø, 3.5 Ø
3 Ø, 2.5 Ø
2 Ø, 1.5 Ø
1 Ø, 1.5 Ø
0 Ø, -0.5 Ø
-1 Ø, -1.5 Ø, -2 Ø, -3 Ø, -4 Ø
Data Processing
All replicates for each station were combined to give a total abundance for each station prior
to analyses. A data matrix of all the combined faunal abundance data was compiled and
used for statistical analyses. The faunal analysis was carried out using the PRIMER ®
(Plymouth Routines in Multivariate Ecological Research) programme.
Univariate statistics in the form of diversity indices were calculated on the combined replicate
data. The following diversity indices were calculated:
1) Margalef’s species richness index (D), (Margalef, 1958).
D
S 1
log2N
where: N is the number of individuals
S is the number of species
2) Pielou’s Evenness index (J), (Pielou, 1977).
H' (observed)
J=
'
Hmax
where: H'max is the maximum possible diversity, which could be achieved if all species were
equally abundant (= log2S)
3) Shannon-Wiener diversity index (H'), (Pielou, 1977).
S
H' = - ¦i=1 pi (log2 pi )
where: pI is the proportion of the total count accounted for by the ith taxa
Species richness is a measure of the total number of species present for a given number of
individuals. Evenness is a measure of how evenly the individuals are distributed among
different species. The diversity index incorporates both of these parameters. Richness
ranges from 0 (low richness) to 12 (high richness), evenness ranges from 0 (low evenness)
to 1 (high evenness), diversity ranges from 0 (low diversity) to 5 (high diversity).
The PRIMER ® manual (Clarke & Warwick, 2001) was used to carry out multivariate
analyses on the station-by-station faunal data. It must be noted here that the species that
were present only once or twice in the survey were excluded from the multivariate analysis.
6-29
All species/abundance data were fourth root transformed and used to prepare a Bray-Curtis
similarity matrix in PRIMER ®. The fourth root transformation was used in order to downweigh the importance of the highly abundant species and allow the mid-range and rarer
species to play a part in the similarity calculation. The similarity matrix was then used in
classification/cluster analysis. The aim of this analysis was to find “natural groupings’ of
samples, i.e. samples within a group that are more similar to each other, than they are
similar to samples in different groups (Clarke & Warwick, loc. cit.). The PRIMER ®
programme CLUSTER carried out this analysis by successively fusing the samples into
groups and the groups into larger clusters, beginning with the highest mutual similarities then
gradually reducing the similarity level at which groups are formed. The result is represented
graphically in a dendrogram, the x-axis representing the full set of samples and the y-axis
representing similarity levels at which two samples/groups are said to have fused. The
CLUSTER programme was set to include a series of ‘similarity profile’ (SIMPROF)
permutation tests, which look for statistical evidence of genuine clusters in samples which
are a priori unstructured. SIMPROF performs tests at every node of a completed
dendrogram, that the group being sub-divided has ‘significant’ internal structure. The test
results are displayed in a colour convention on the dendrogram plot (samples connected by
red lines cannot be significantly differentiated).
The Bray-Curtis similarity matrix was also subjected to a non-metric multi-dimensional
scaling (MDS) algorithm (Kruskall & Wish, 1978), using the PRIMER ® program MDS. This
programme produces an ordination, which is a map of the samples in two- or threedimensions, whereby the placement of samples reflects the similarity of their biological
communities rather than their simple geographical location (Clarke & Warwick, 2001). With
regard to stress values, they give an indication of how well the multi-dimensional similarity
matrix is represented by the two-dimensional plot. They are calculated by comparing the
interpoint distances in the similarity matrix with the corresponding interpoint distances on the
2-d plot. Perfect or near perfect matches are rare in field data, especially in the absence of a
single overriding forcing factor such as an organic enrichment gradient. Stress values
increase not only with the reducing dimensionality (lack of clear forcing structure), but also
with increasing quantity of data (it is a sum of the squares type regression coefficient).
Clarke and Warwick (loc. cit.) have provided a classification of the reliability of MDS plots
based on stress values, having compiled simulation studies of stress value behaviour and
archived empirical data. This classification generally holds well for 2-d ordinations of the type
used in this study and the threshold stress values are shown below:
x
x
x
x
Stress value < 0.05: Excellent representation of the data with no prospect of
misinterpretation.
Stress value < 0.10: Good representation, no real prospect of misinterpretation of
overall structure, but very fine detail may be misleading in compact subgroups.
Stress value < 0.20: This provides a useful 2-d picture, but detail may be
misinterpreted particularly nearing 0.20. Stress value 0.20 to 0.30: This should be
viewed with scepticism, particularly in the upper part of the range, and discarded for a
small to moderate number of points such as < 50.
Stress values > 0.30: The data points are close to being randomly distributed in the 2d ordination and not representative of the underlying similarity matrix.
6-30
Each stress value must be interpreted both in terms of its absolute value and the number of
data points. In the case of this study, the moderate number of data points indicates that the
stress value can be interpreted more or less directly. While the above classification is
arbitrary, it does provide a framework that has proved effective in this type of analysis.
SIMPER analysis was then carried out on the transformed data to determine the
dominant/characterising species within each group identified by the CLUSTER/SIMPROF
analysis.
6.2.3.3.3
Results
FAUNA
The taxonomic identification of the benthic infauna across all 15 stations sampled in Sligo
Harbour yielded a total count of 110 species accounting for 2,303 individuals, ascribed to 8
phyla. A complete listing of these species abundance is provided in Appendix 4C, which is
located on the accompanying data DVD-ROM.
Of the 110 species enumerated, 43 were annelida (segmented worms), 29 were crustaceans
(crabs, shrimps, prawns), 32 were molluscs (mussels, cockles, snails etc.), 2 species were
arthropods (insects, spiders), 1 species was a nematode (round worm), 1 was a nemertean
(ribbon worm), 1 was a chelicerata (sea spider) and 1 species was a plathyhelminth
(flatworm).
x
Univariate Analyses
Univariate statistical analyses were carried out on the combined replicate station-bystation faunal data. The following parameters were calculated and can be seen in Table
6.3: species numbers, number of individuals, richness, evenness and diversity. Species
numbers ranged from 2 (Stations 5 and 15) to 35 (Station 1). Number of individuals
ranged from 2 (Station 5) to 1073 (Station 7). Richness ranged from 0.25 (Station 15) to
6.97 (Station 4). Evenness ranged from 0.1 (Station 7) to 1.00 (Stations 5 and 10).
Diversity ranged from 0.13 (Station 15) to 4.39 (Station 4).
6-31
Table 6.3: Diversity indices for the 15 stations sampled in Sligo Harbour.
Station
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
x
Species
35
5
28
31
2
11
8
5
32
6
3
14
7
7
2
Individuals
139
11
320
74
2
170
1073
21
184
6
4
169
24
50
56
Richness
6.89
1.67
4.68
6.97
1.44
1.95
1.00
1.31
5.94
2.79
1.44
2.53
1.89
1.53
0.25
Evenness
0.84
0.86
0.54
0.89
1.00
0.39
0.10
0.63
0.74
1.00
0.95
0.52
0.79
0.45
0.13
Diversity
4.29
2.00
2.58
4.39
1.00
1.36
0.29
1.47
3.68
2.58
1.50
1.99
2.21
1.26
0.13
Multivariate Analyses
The dendrogram and the MDS plot can be seen in Figure 6.31 and Figure 6.32
respectively. Five groupings were identified through the SIMPROF programme. These
are as follows:
Group a: Stations 1, 3, 6, 7, 9, 11 and 12
Group b: Stations 2, 5 and 10
Group c: Station 15
Group d: Station 4; and
Group e: Stations 8, 13 and 14.
Groups b and e consisted of sandy stations located within or close to the navigation
channel in the harbour. Group a consisted of sand, gravelly muddy sand, sandy gravel
and slightly gravelly muddy sand stations and all were located within the harbor area.
Stations 4 (slightly gravelly sand) and station 15 (no granulometric data) were located
outside the harbor and grouped separately from all the other stations.
Group a formed at a similarity level of 12.5%. The 7 stations in this group accounted for
80 different species comprising 2,059 individuals. Of the 80 species present, 37 were
present more than twice. Five species accounted for 80% of the abundance in this
group: the gastropod mollusc Hydrobia ulvae (1,326 individuals; 64.4%), the
oligochaete Tubificoides benedii (162 individuals; 7.9%), the bivalve mollusc
Parvicardium pinnulatum (3 individuals; 3.6%), the barnacle Balanus crenatus (65
individuals; 3.2%) and the oligochaete Tubificoides pseudogaster agg. (31 individuals;
1.5%). This group had an average within group similarity of 21.33% according to
SIMPER analysis (See Table 6.4).
Group b formed at a similarity level of 50.36%. The 3 stations in this group accounted
for 8 different species comprising 19 individuals. Of the 8 species present, 3 were
6-32
present more than twice. Three species accounted for 74% of the abundance in this
group: the polychaete Scoloplos armiger (6 individuals; 32%); the bivalve mollusc
Tellina sp. (5 individuals; 26%) and the polychaete Eteone longa agg. (3 individuals;
16%). This group had an average within group similarity of 50.61% according to
SIMPER analysis (See Table 6.4).
Group c consisted of station 15 only. This station contained 2 species and 56
individuals. The bivalve mollusc Donax vittatus accounted for 55 of the individuals (98%
of the abundance). Within group similarity could not be calculated for this group
because it only contained 1 station.
Group d consisted of station 4 only. This station contained 31 species and 74
individuals. Of the 31 species present, 14 were present more than twice. The bivalve
mollusc Donax vittatus was also the dominant species at this station but in significantly
lower numbers than at station 15 (Group c). Four species accounted for 46% of the
abundance in this group: Donax vittatus (12 individuals; 16%), the polychaetes Nephtys
cirrosa (9 individuals; 12%) and Scoloplos armiger (7 individuals; 9%) and the bivalve
mollusc Tellina sp. (6 individuals; 8%). Within group similarity could not be calculated for
this group because it only contained 1 station.
Group e formed at a similarity level of 49.22%. The 3 stations in this group accounted
for 12 different species comprising 95 individuals. Of the 12 species present, 4 were
present more than twice. These four species accounted for 88% of the faunal
abundance: the bvivalve mollusc Tellina tenuis (64 individuals; 67%), the polychaete
Nephtys cirrosa (13 individuals; 14%) and the molluscs Retusa obtusa (4 individuals;
4%) and Mytilidae sp. (3 individuals; 3%). This group had an average within group
similarity of 55.88% according to SIMPER analysis (see Table 6.4). Table 6.4 also
shows the characterizing species for each group.
These delineations were also preserved in the MDS plot. The stress value of the MDS
ordination is 0.1; which results in a good representation with no real prospect of
misinterpretation of the overall structure, but the very fine detail may be misleading in
compact subgroups.
6-33
Figure 6.31: Dendrogram showing the natural grouping of each station sampled in
Sligo Harbour.
Figure 6.32: MDS ordination showing the natural grouping of each station sampled in
Sligo Harbour.
6-34
Table 6.4: SIMPER Results
Group a Average similarity: 21.33
Species
Av.Abund
Av.Sim
Sim/SD
Contrib%
Cum.%
Hydrobia ulvae
Tubificoides benedii
Cardiidae sp. (juv)
Tubificoides pseudogaster agg
Parvicardium pinnulatum
Pygospio elegans
Capitella sp.
Macoma balthica
Cerastoderma edule
Eteone longa aggregate
Abra alba
Aoridae sp.
Platynereis dumerilii
2.23
1.34
0.95
1.08
1.03
0.86
0.67
0.6
0.69
0.64
0.29
0.51
0.57
3.99
3.04
2.62
2.09
1.55
1.39
1.08
1.03
0.83
0.56
0.49
0.42
0.34
0.76
0.79
0.79
0.87
0.49
0.58
0.59
0.59
0.6
0.39
0.22
0.39
0.4
18.69
14.23
12.3
9.79
7.27
6.51
5.06
4.84
3.9
2.62
2.32
1.99
1.59
18.69
32.92
45.22
55.01
62.27
68.78
73.85
78.69
82.59
85.21
87.53
89.51
91.11
Group b Average similarity: 50.61
Species
Av.Abund
Av.Sim
Sim/SD
Contrib%
Cum.%
Eteone longa aggregate
Scoloplos armiger
Tellina sp. (juv)
1
1.14
0.8
22.49
22.49
5.64
4.65
4.65
0.58
44.43
44.43
11.14
44.43
88.86
100
Group d - Less than 2 samples in group
Group e Average similarity: 55.88
Species
Av.Abund
Av.Sim
Sim/SD
Contrib%
Cum.%
Tellina tenuis
2.09
23.42
10
41.91
41.91
Nephtys cirrosa
Mytilidae sp. (juv)
1.41
1
15.73
12.41
6.23
11.19
28.16
22.22
70.07
92.28
Group c - Less than 2 samples in group
SEDIMENT
The results from the traditional granulometric analysis can be seen in Table 6.5. Figure 6.33
shows these data in graphical form. The sediment sampled during the survey was classified
as sand, slightly gravelly sand, sandy gravel, slightly gravelly muddy sand and gravelly
muddy sand according to Folk (1954). Figure 6.34 shows the sediment type according to
Folk’s (1954) classification.
The majority of stations were classified as sand (Stations 2, 3, 5, 7, 8, 10, 12, 13 and 4) (See
Figure 6.33 and Figure 6.34). All of the stations sampled within the harbour area (i.e. inside
Oyster Island) were classified as sand with the exception of the two inner stations (stations
11 and 6) and station 1 located approximately 300m northeast of Oyster Island. Station 1
was classified as sandy gravel, station 6 as slightly gravelly muddy sand and station 11 as
gravelly muddy sand. Outside the harbour area, Station 4 was classified as slightly gravelly
sand.
6-35
Station 1 contained the highest percentage of gravel (68.5%). Station 9 contained the
highest percentage of very coarse sand (10.2%) and coarse sand (8.3%). Station 14
contained the highest medium sand fraction (33.5%). Station 12 contained the highest fine
sand (89.3%). Station 2 contained the highest very fine sand (15.6%) and station 11
contained the highest silt-clay (16.8%).
Table 6.5: Granulometry results for the 14 stations sampled in Sligo Harbour (as
percentage weight of the total sample).
Stn
Gravel
Very
Coarse
Medium
Fine
Very
(%)
Coarse
Sand (%)
Sand (%)
Sand
Sand (%)
Sand (%)
(%)
Fine
Silt-
Folk (1954)
Clay
(%)
1
68.5
7.7
4.6
4
9.5
4.9
0.9
Sandy gravel
2
0.7
1.1
1.7
4.8
75
15.6
1
Sand
3
0.2
0.3
0.5
2.7
81.7
9.3
5.2
Sand
4
3.4
1.4
2.3
8.1
81.7
3.1
0.1
Slightly gravelly sand
5
0.5
0.6
1.5
3.8
77.3
14.1
2.1
Sand
6
1.3
1.4
1.5
3.6
58.4
20.9
13
Slightly
gravelly
muddy sand
7
0.1
0.3
0.4
6.1
85.3
7.2
0.5
Sand
8
0.8
2.4
6.4
26.8
60.2
3.2
0.1
Sand
9
51
10.2
8.3
9.8
15.4
4
1.2
Sandy gravel
10
0
0.1
0.3
5.1
89.2
5.3
0
Sand
11
6.8
2.9
2
3.1
46.5
22
16.8
Gravelly muddy sand
12
0.2
0.3
0.6
3.3
89.3
5.8
0.5
Sand
13
0.2
1.7
3.3
13.4
79.5
1.8
0
Sand
14
0.6
1.8
5.4
33.5
56.5
2.2
0
Sand
*The particle size ranges for each classification (gravel, very coarse sand, coarse sand,
medium sand, fine sand, very fine sand and silt clay) is adapted from Buchanan (1984) and
can be seen in Table 6.2. The classifications according to Folk (1954) are based on varying
percentages of gravel, sand and silt-clay.
6-36
Figure 6.33: Sediment grain size data
Figure 6.34: Sediment type according to Folk (1954)
6-37
ORGANIC CARBON
Sediment samples were taken for organic carbon analysis. Samples were sent to SAL
(Scientific Analysis Laboratories, Manchester, England – a UKAS and UK Environment
Agency MCERTS accredited laboratory) for total organic Carbon (TOC) determination.
Table 6.6: Sediment organic carbon results for the fourteen stations surveyed off
Sligo, 6th October, 2010.
Station
Determinand
Units
1
2
3
4
5
6
7
8
9
10
11
12
13
14
TOC
%
2.0
2.1
1.5
0.3
1.6
3.8
1.6
1.7
3.1
2.6
5.2
1.5
1.1
1.6
6.2.4 Sligo Harbour Intertidal and Subtidal Flora and Fauna - Predicted Impacts
The impact assessment has been undertaken with due regard to the EPA’s “Advice Notes
on Current Practice” (2003); the EPA’s “Guidelines on the information to be contained in
Environmental Impact Statements” (2003); with reference to the discipline-specific Institute
of Ecology and Environmental Management’s “Guidelines for Ecological Impact
Assessment“ (IEEM, 2006) and the National Roads Authority (NRA)’s “Guidelines for
Ecological Impact Assessment”.
Criteria for assessing impact level have been derived from those set out in Appendix 4 of the
NRA discipline specific EcIA Guidelines (2004), but expanded in order to be able to address
issues such as habitat quality and are shown in Appendix 4D of this report. Terminology for
impact significance and duration follows that set out by the EPA (2003) in its generic
guidelines.
6.2.4.1 Consideration of Significance
In terms of significance, the NPWS Guidance (2010 Rev) uses an EC definition as
follows:..”any element of a plan or project that has the potential to affect the conservation
objectives of a Natura 2000 site, including its structure and function, should be considered
significant (EC, 2006)”. Other guidance documents also discuss significance criteria, some in
more detail than others. The Dutch Guidance1 (2004) discusses a number of criteria in
relation to habitats and species population.
In general, significance indicators might include:
x
impact on Annex I habitat (including loss or reduction in size - percentage relative to
the overall area of the habitat in the Natura site; impairment of function);
x
fragmentation of habitat or population (depending upon the duration or permanence);
x
disturbance (noise, light etc. - distance, duration);
x
effect on species populations (direct or indirect damage to size, breeding patterns etc);
1
Translated from Publication of Dutch State Printers in book:’Praktijkboek Habitattoets’ , 2004 (F. Neumann en H. Woldendorp,
SDU)
6-38
x
changes in water quality.
To summarise the significance issue, it is useful to quote from Morris (2008) who describes
significance in the context of the Habitats Directive as follows: “...Within the Habitats
Regulations, significance is quite different. It is used as a coarse filter and the test is a
question over the possibility that there will be a significant effect on a key receptor that
determines the conservation status of a European site. Thus, determining whether there will
be a ‘likely significant effect’ does not imply that there will be such an effect or even that
such an effect is more likely than not; it simply flags the need to test the issues and then
make a judgement of the pathways and mechanisms imposed by a project on the
designated wildlife interest. This test best equates to the screening and scoping opinions
sought for an EIA but is confined to the Natura 2000 and Ramsar interest rather than wider
environmental or nature conservation issues”.
In order to assess the likely impacts and ascertain whether a significant impact on the
integrity of the Natura site(s) is likely to occur as a result of the proposed development,
should the appropriate assessment process deemed to be required, it is necessary to
consider what constitutes the integrity of a Site as referred to in Article 6(3). The document
Managing Natura 2000 Site, The provisions of Article 6 of the ‘Habitats’ Directive 92/43/EEC
(2000) gives clear guidance in this regard and states: “The integrity of the site involves its
ecological functions. The decision as to whether it is adversely affected should focus on and
be limited to the site’s conservation objectives”.
Integrity has been discussed and defined in various ways in guidance documentation and
the literature. For example, Treweek (1999) discusses biological integrity and ecosystem
health, and refers to three generally accepted criteria: systematic indicators of ecosystem
functional and structural integrity; ecological sustainability or resilience (relating to the ability
of a system to withstand “natural” or anthropogenic stresses); and absence of detectable
symptoms of ecosystem disease or stress. A similar, but less academic, approach is
adopted by the various guidance documents with a number of definitions proposed. The
essence of the concept of ecological integrity is distilled in the following definition from
Planning Policy Statement 9 (UK Department of Environment, 1994 – now superseded by
PP9, 2005): “coherence of the site’s ecological structure and function, across its whole area,
or the habitats, complex of habitats and/or populations of species for which the site is or will
be classified”.
6.2.4.2 Potential impacts on Natura 2000 sites – impacts prediction
Criteria for assessing impact level have been derived from those set out in Appendix 4 of the
NRA EcIA Guidelines (2004) criteria and expanded in order to be able to address issues
such as habitat quality. Terminology for impact significance and duration follows that set out
by the EPA (2003). The potential impact magnitude described in the following sections,
without mitigation, is negative unless otherwise stated as being positive or neutral. Where
the impact is stated as being localised, it refers to the immediate area of impact.
6-39
6.2.4.2.1
Potential impacts on Cummeen Strand/Drumcliff Bay SAC
Potential impacts on habitats in Cummeen Strand/Drumcliff Bay SAC
Qualifying marine habitats for the Cummeen Strand/Drumcliff Bay SAC:
The proposed dredging scheme will have a direct impact on the Mudflats and Sand
flats/Estuarine habitats in Sligo Harbour. This impact may be divided into two parts:
a) The removal of sediments from the estuarine environment
b) The suspension of sediments in the water column as a result of the dredging
operation and the subsequent deposition of some of this material over parts of the
mudflats and sandflats in Sligo Harbour
a) The removal of estuarine sediments
There will be a loss of benthic habitat along the navigational channel as a result of
sediment removal. Along the channel where dredging occurs, removal of all surface
sediment and associated fauna will occur over a relatively short time frame. (The
dredging will extend across an area of up to 271,910m², which is 0.56% of the SAC area
(48,541,373m²).
b) Deposition of sediments on mudflats and sandflats
Based on the results of the hydrodynamic sediment transport model attached in Chapter
11, during the proposed dredging operations, sediment put into suspension by the
dredger during water injection dredging will be dispersed around the northern portion of
Sligo Harbour. The sediment will be redistributed during periods of higher current
velocities during successive spring tides, before eventually coming to rest in small
deposits around the fringes of Sligo Harbour and Cartron Marsh (see Figure 11.8 in
Chapter 11). Some of the material will be successfully transported out of the harbour
and will settle out on the nearby sand banks in depths of a few mm.
During conventional dredging small amounts of sediment put in to suspension by the
dredger will be temporarily deposited along the sides of the navigation channel and in
sheltered areas along the north shore of the harbour area.
The areas that will experience the greatest amount of temporary sedimentation occur
along the north shoreline of Sligo Harbour (peak sedimentation during dredging of 2070mm). It should be noted that these peak values are typically of a short duration (a
matter of hours) and tend to occur during slack tide. The material may then be resuspended and transported elsewhere as the tidal currents pick up during the
conventional dredging operations is shown in Figure 11.26 in Chapter 11. This shows
that the maximum final deposition depth following completion of operations does not
exceed 1mm in the majority of the harbour area and exceeds 25mm only in very
localised areas around the navigation channel and the northern shore of the harbour.
Post dredging, the modelled area in which there will be residual deposits of sediment in
excess of 25mm is approximately 35,078m². These deposits will be mainly concentrated
6-40
in the lee of the training wall. The area of habitat which will experience residual
deposition in excess of 25mm represents approximately 0.18% of the SAC habitat
“Mudflats and sandflats not covered by seawater at low tide” or 0.07% of the overall SAC
area.
Potential impacts on qualifying species and listed species for the Cummeen
Strand/Drumcliff Bay SAC
Once dredging ceases, recovery of the dredged area follows. In a harbour navigation
channel where both maintenance and capital dredging are routinely carried out, this cycle of
regular disturbance and subsequent recovery has played out as long as the channel has
existed and will continue to do so for as long as the channel is maintained and used. The
benthic environment surrounding the Sligo Harbour navigation channel exists in its current
form after a long history of similar periodic disturbance. The typical phases of recovery
following dredge disturbance are outlined below.
Recovery begins with the colonization of the defaunated area by small opportunistic species
adapted to survive in areas of physical disturbance. This colonization occurs either from
neighbouring sites or via larval settlement or both. Few organisms follow this life style
strategy so there is a tendency for a limited number of species to reach extremely high
densities in the presence of pollutants. The bioturbatory activities of these infauna start to
significantly modify the physical, chemical and biological nature of the deposit. The
macrofaunal assemblage enters a ‘transitory’ phase of succession when the sedimentary
changes allow further colonization of a larger variety of species. This stage is unfavourable
for the ‘pioneer’ population to persist. Species that characterise the transitory sere include
suspension and deposit feeding bivalves, ‘conveyor belt’ polychaetes and relatively immobile
holothurians. Here again the physical and chemical properties of the sediment are further
modified by the new infaunal dominants making way for additional species to take hold. A
more complicated and persistent faunal assemblage now forms and evolves towards an
‘equilibrium’ or ‘climax’ community status
What is described above is typical of recovery from a physical disturbance like dredging.
This recovery sequence is applicable if there is no subsequent disturbance to the site. While
there will be a loss of infaunal habitat due to the removal of sediment from an area of up to
271,910m² (which is 0.56% of the SAC area), recolonisation of denuded habitat will occur
quickly and the floral and faunal communities inhabiting the qualifying habitats in the SAC
will not be permanently impacted.
Qualifying plant species for the SAC
No qualifying marine plant species listed for this SAC.
Listed bird species for the SAC – Annex I species (EU Birds Directive) - Please refer to
Chapter 6, “Birds”
Mammal species for the SAC – Annex II species (EU Habitats Directive)
Please refer to Section 6.4 of this Chapter, “Marine Mammals”.
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Qualifying Annex II and listed fish species for the SAC
Cummeen Strand/Drumcliff Bay SAC
Both the river lamprey (Lampetra fluviatilis) and the sea lamprey (Petromyzon marinus) are
listed for the Cummeen Strand/Drumcliff Bay SAC. These two species both spawn in rivers
and both occur in coastal and estuarine environments – though L. fluviatilis tends to remain
closer to the coast than P. marinus. Additional detail on lamprey migration is presented in
Chapter 7, “Fisheries and Aquaculture”.
On migrating through estuarine environments these species may frequently encounter high
suspended sediment loads, which do not appear to impact on migrations.
Projected levels of suspended sediment during dredging operations are within
recommended guidelines and will not have an adverse effect the upstream and downstream
migrations of eels and lamprey.
Lough Gill SAC
The adjoining Lough Gill SAC (Site Code: 001976) is of considerable importance for the
presence of four Red Data Book fish species that are listed on Annex II of the E.U. Habitats
Directive - Brook Lamprey (Lampetra planeri), River Lamprey (Lampetra fluviatilis), Sea
Lamprey (Petromyzon marinus) and Atlantic Salmon (Salmo salar).
It is likely that the three migratory species of the above – salmon and river and sea lamprey
– use the Sligo Harbour navigation channel during migrations to and from the Lough Gill
SAC.
More detailed information on salmonids is presented in Chapter 7, “Fisheries and
Aquaculture”.
Fish migrating through estuarine environments may frequently encounter high suspended
sediment loads which do not appear to impede this behavioural activity. Atlantic salmon are
known to move through the Severn Estuary where sediment concentrations in suspension
can reach into several thousand mg/l for periods (Gibson, 1933). Simenstad (1988) suggests
that salmonids are likely to have adapted physiologically to the turbid conditions that occur
naturally within estuarine and harbour areas.
Suspended sediment concentrations in the lower 0.5m of water column are predicted to
remain relatively low throughout dredging operations. Adult salmonids are most likely to
move upstream via the navigation channel where the mean concentration be slightly higher
but will remain within the Fish Directive recommended limit of 25 mg/l for salmonid waters.
Moreover, suspended sediment concentrations are likely to be lower in the upper layers of
the water column which salmon more commonly utilise when swimming through estuarine
and coastal waters.
Projected levels of suspended sediment are within recommended guidelines and will not
have an adverse effect the upstream and downstream migration of salmonids.
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Otter (Lutra lutra) (Annex II and IV)
Otter are listed in the Conservation objectives for the adjoining Lough Gill SAC. Though not
listed, this species also occurs in the Cummeen Strand/Drumcliff Bay SAC. The proposed
dredging scheme will not have an effect on the type of substrate primarily used by otters for
foraging i.e. the littoral and shallow sublittoral zones. Due to the adaptability and mobility of
this species, it is unlikely that the intermittent temporary dredging works will have a
significant negative effect on these animals.
Marine mammals (Annex II and Annex IV)
No cetaceans are listed as qualifying species for the Cummeen Strand/Sligo Harbour SAC,
or as being of special importance to the SAC. The dolphins and harbour porpoises recorded
in the Cummeen Strand/Sligo Harbour SAC are highly mobile species. Due to the shallow
depths that characterise this area it is likely that they use this site primarily at high water.
They are able to detect noise and vibration at great distances and are unlikely to be
impacted by either a plume of suspended sediment (as they rely primarily on hearing, as
opposed to vision for navigation) or the physical presence and activity of a dredger. As they
are air-breathing mammals, the presence of an elevated level of suspended matter in the
water column is of no consequence to these species.
A full examination of the potential impacts on marine mammals is presented in Section 6.4
this chapter.
Other fish species
Due to their mobility, impacts to fish species occurring subtidally in the Cummeen
Strand/Sligo Bay SAC are likely to be negative, slight and short-term. Fish are very sensitive
to vibration and disturbance in the water column and quickly relocate when disturbed. It is
likely that demersal and pelagic fish species that become acclimatised to the dredging
pattern will learn to avoid the dredge plume (relocating upstream of the tidal flow) and will
enter the dredged area to scavenge on exposed, dead or moribund infauna left behind on
the seafloor in the wake of the dredging operation (when dredging ceases as low tide is
approaching). It is not uncommon that elevated numbers of scavenging fauna are noted in
areas where the seafloor has been subject to physical disruption/disturbance.
Having undergone a sharp decline in recruitment from 1980, European eel (Anguilla
anguilla) is now listed as CR – critically endangered on the IUCN (International Union for
Conservation of Nature) Red Data List. A population of eel exists in Lough Gill and it is likely
that they use the navigation channel area during migrations to and from their distant
breeding grounds. All possible measures should be taken to minimise disturbance to this
species during migration through the estuarine environment as the next classification level in
the IUCN Red Data List is EW – extinct in the wild. On migrating through estuarine
environments eels may frequently encounter high suspended sediment loads which do not
appear to impact on migrations.
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Projected levels of suspended sediment during dredging operations are within
recommended guidelines and will not have an adverse effect the upstream and downstream
migrations of eels.
Potential impacts on the macrobenthos - food source for SPA bird species
Intertidal macrobenthos is of greatest value to bird species as a food source (due to
accessibility). The subtidal infaunal macrobenthos along the floor of the navigation channel
will be subject to the greatest level of impact (complete removal, though with potential for
rapid recolonisation). Impacts to the intertidal macrobenthos are likely to be imperceptible,
localised and temporary, as the continued movement of the dredger along the navigation
channel will ensure that any given area will not be impacted for a protracted period.
The hydrodynamic modelling presented in Chapter 11 shows that the sediment put into
suspension by the dredger during water injection dredging will be dispersed around the
northern portion of Sligo Harbour. The sediment will be redistributed during periods of
higher current velocities during successive spring tides, before eventually coming to rest in
small deposits around the fringes of Sligo Harbour and Cartron Marsh (see Figure 11.8 in
Chapter 11). Some of the material will be successfully transported out of the harbour and
will settle out on the nearby sand banks in depths of a few mm.
During subsequent conventional dredging, small amounts of sediment put in to suspension
by the dredger during dredging operations will be temporarily deposited along the sides of
the navigation channel and in sheltered areas along the north shore of the harbour area.
The areas that will experience the greatest amount of temporary sedimentation occur along
the north shoreline of Sligo Harbour (peak sedimentation during dredging of 20-70mm).
These peak values are typically of a short duration (a matter of hours) and the material may
then be re-suspended and transported elsewhere as the tidal currents pick up during the
conventional dredging operations is shown in Figure 11.26 in Chapter 11. This shows that
the maximum final deposition depth following completion of operations does not exceed
1mm in the majority of the harbour area and exceeds 25mm only in very localised areas
around the navigation channel and the northern shore of the harbour. Overall, the amount of
sediment deposited in the harbour area as a result of the dredging will be insignificant. No
residual impact is expected.
Noise impact on benthos
Impacts on benthos from noise in the vicinity of the dredging operation are expected to be
localised and temporary. The fact that the proposed dredging will take place in an already
busy port navigation channel suggests that the additional, temporary noise loading of a
dredger at work would be of minimal significance to benthos in the vicinity of the dredged
area.
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Bivalve Beds
Blue mussels (Mytilus edulis) are filter-feeding bivalves that have a very high efficiency in
removing particulate matter (phytoplankton, organic matter and suspended sediment) from
the water column to an extent that food for the bivalves may become a limiting resource at
the sediment-water interface. This high efficiency at removing particulate matter from the
water column directly relates to the potentially adverse effects of dredging-induced sediment
plumes on these filter feeding bivalves. Large quantities of suspended sediment in the water
column can be detrimental due to clogging of the gills and impairment of proper respiratory
and excretory functioning and feeding activity. Overall, research suggests that the degree of
an impact on filter-feeding species depends on the extent of turbidity and sedimentation
against background levels. Benthic shellfish in normally turbid environments (such as that
found in the Cummeen Strand area) are probably able to survive smothering unless the rate
of deposition is excessive. Studies also show that filter feeders, and bivalves in particular,
are highly adaptable in their response to increased suspended sediment levels from, for
example, periodic storms and dredging, maintaining their feeding activities over a wide range
of particulate loads and suspended sediment concentrations (Newell et al., 1998).
Previous studies on effects of suspended sediments on adult mussels (Mytilus edulis) have
shown that they are capable of coping with extreme high concentrations of suspended
material (Kiørboe et al., 1980). In one recent study, a no effects level of 1,867 mg/L for
Mytilus edulis has been reported (Anchor Environmental, 2003). In laboratory studies, lethal
concentrations for adult bivalves exposed for as long as 3 weeks were in the realm of fluid
mud, i.e. around 10,000 mg/L (Clarke & Wilbur, 2000). The ability for mussels to effectively
utilize suspended food particles for growth is optimal at concentrations below 50 mg/L.
Concentrations above 100 mg/L result in weight loss (Prins & Smaal, 1989). The growth rate
of common mussels increased in a field experiment in Denmark, where mussels were
regularly exposed to silt concentrations between 200-250 mg/L in a plume originating from
dumping of dredged spoil during a period of five weeks (Birklund & Wijsman, 2005). The
high concentrations did not affect the survival of the mussels. Mussels can protect
themselves from overloading by temporarily closing the valves and the closing response
depends on the size of the mussels. Widdows et al. (1979) demonstrated that maximum
filtering rates by 3cm long mussels (Mytilus edulis) (from an area that had a natural range in
suspended matter between 5 and 35 mg/L) were found at suspended matter concentrations
of 125mg/L, 30% reduced at 225mg/L and negligible at concentrations >250 mg/L. Larger
mussels (7 cm) stopped filtering and closed their valves at 350 mg/L. When mussels are
given sufficient time (months), they can adapt their gills and palps to higher concentrations of
suspended matter up to concentrations as high as 400 mg/L (Essink et al., 1989).
Suspended bottom material, which is always present in the natural habitats of the blue
mussel Mytilus edulis, serves as an important additional food source for the mussels. Mytilus
edulis depends on this suspended bottom material to exploit fully its clearance potential and
reach the maximum growth rates observed in nature (Kiørboe et al., 1980). Field research in
the Ems Estuary (The Netherlands) indicated that a 10-20% increase in turbidity did not
have negative impacts on the growth and survival of mussels (Essink et al., 1990).
6-45
In instances of incidental deposition, sessile benthic species such as mussels have a
relatively low tolerance of sediment cover. Adult mussels in a mussel bed are not capable of
moving upwards after deposition of layers of mud or sand and deposition of a layer of 1-2cm
within a relatively short period can be considered fatal to mussels (Essink, 1999).
Based on the above information, the tolerance thresholds of mussel beds is summarised in
Table 6.7.
Table 6.7: Summary of critical thresholds for mussel (Mytilus edulis) beds.
Species
Mytilus
edulis
Parameter
Suspended
sediment
Optimum Range
<1867 mg/l
50-100 mg/l
<250 mg/l (5 weeks)
<400 mg/l (turbid estuaries)
Sedimentation
Maximum Tolerated
<10,000 mg/k for 3
weeks (adult)
1-2 cm (within short
time)
Impacts of the dredging plume on mussel beds in Sligo Harbour are considered negligible.
Mussels are very tolerant of extremely high turbidities (see Table 6.7).
The proposed dredging scheme will not have any impact on mussels (adults, larvae or spat).
Neither suspended sediment levels nor sedimentation rates demonstrated in Chapter 11,
“Hydrodynamic Modelling” reach lethal levels for mussels.
Zostera Beds
Light is one of the key environmental resources imperative for the growth and survival of
seagrasses (Hemminga & Duarte, 2000). The degree of water transparency (which
determines the depth-penetration of photosynthetically active radiation of sunlight) is the
primary factor determining the maximum depth at which seagrasses can occur. Reduction in
light due to turbidity has been identified as a major cause of the loss of seagrasses
worldwide (Shepherd et al., 1989; Green & Short, 2003). The amount of light that reaches a
seagrass leaf is determined by the natural water colour, concentration of suspended solids,
phytoplankton concentration and the epiphyte cover of the leaf. There are various reports of
sublethal and lethal effects on seagrass meadows due to prolonged exposure to high
turbidity and siltation associated with dredging activities (Erftemeijer & Lewis, 2006).
Laboratory experiments have shown that some seagrasses can survive in light intensities
below their minimum requirements for periods ranging from 4 weeks to several months.
However, widespread seagrass mortality was observed in Chesapeake Bay (USA) following
a month-long (seasonal) pulse of increased turbidity (light extinction coefficient (k)>3.0 m-1)
(Moore et al., 1997).
The minimum light requirements of Zostera marina (eelgrass) have been extensively studied
in a range of locations and environments. The values for the minimum light requirements of
this species, as reported in literature, vary between 11 and 37 % of Surface Irradiance (SI).
For the survival of seagrasses, the lowest value of 11%SI is the most critical level below
which widespread mortality surely occurs. Some of the higher values (up to 37%SI) reported
6-46
for eelgrass appear to refer to the minimum light levels required to enable and sustain lateral
shoot development, meadow expansion and flowering. Levels below 37%SI but above
11%SI do affect these processes, but may not cause substantial eelgrass mortality. There
has been only 1 detailed study of the minimum light requirements for Zostera noltii: Peralta
et al. (2002) reported a minimum light requirement of 2% of SI for Zostera noltii in Spain.
According to the same study (also reported in: MarLIN Database, 2006), Zostera noltii plants
can tolerate acute light reduction below 2% SI for up to two weeks, and thus appear tolerant
of short-term events of very high turbidity. A recent monitoring study into the effects of a
dredging plume on intertidal eelgrass (Zostera marina) in the Ems Estuary (The
Netherlands) during (day-time) periods of low tide exposure (Ochieng & Erftemeijer, 2009).
This implies that intertidal eelgrass plants are relatively tolerant to further turbidity increases
such as may be caused by a dredging plume (Ochieng and Erftemeijer, 2009). Based on the
above information, the tolerance thresholds of seagrass beds to turbidity is summarised in
Table 6.8.
Table 6.8: Tolerance thresholds of Zostera spp. to turbidity levels.
Seagrass Species
Zostera marina
Zostera noltii
Minimum Tolerated
Optimum Range
11-37% SI
>37% SI
2% SI can tolerate acute light reduction
below 2% SI for 2 weeks
Several studies have documented deterioration of seagrass meadows by smothering due to
excessive sedimentation (Erftemeijer and Lewis, 2006). Seagrass species that develop
vertical shoots may respond to fluctuations in sediment depth by modifying their vertical
growth but there are limits to the level of sedimentation seagrasses can tolerate.
Sedimentation rates of as much as 1013 cm yr-1 have been reported as maximum threshold
of what some seagrass species can survive. Settlement of suspended material on leaf
blades of seagrasses may interfere significantly with photosynthesis, and appears especially
significant in low wave energy environments where fine sediments are present and can
settle out. A maximum allowable sedimentation rate of 2 cm in 4 months was reported for
Mediterranean Zostera noltii (Spain). Tolerance of Zostera noltii in the Dutch Wadden Sea
was documented to range from minor erosion of 2 cmyr-1 to maximum sedimentation levels
of 25 cm yr-1. Mortality of 75% was reported for Zostera marina meadows (USA) at burial
with 4 cm (i.e. 25% of plant height), which demonstrates that this species is probably more
sensitive to sedimentation than some of the other (taller) seagrass species. Vermaat et al.
(1997) proposed an estimate of the annual sedimentation rates that can be survived or
escaped by seagrasses, either vertically or horizontally, to be in the order of 5-10 cm yr-1.
Based on the above information, the tolerance thresholds of seagrass beds to sedimentation
is summarised in Table 6.9.
Table 6.9: Tolerance thresholds for Zostera spp. to sedimentation.
Seagrass Species
Zostera marina
Minimum Tolerated
Maximum Tolerated
75% mortality at 4cm/day (25%
of plant height
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Zostera noltii
-1 to -2 cm/yr (erosion)
2-5 cm/year (sedimentation)
2cm / 4 months
Impacts of the dredging plume on the seagrass beds in Sligo Harbour are considered
negligible, because the plumes of high turbidity and sedimentation do not reach the
seagrass beds documented in the area. Besides, intertidal seagrass is probably not affected
much by increased turbidity anyway, since it obtains most of its light during (day-time)
periods of low tide exposure (see Ochieng & Erftemeijer, 2009). Based on the final sediment
deposition depth computed for the Cummeen Strand seagrass habitat, on completion of all
dredging activities, no residual impact on this habitat is expected.
Indirect Impacts on sites in the wider locality, including Lough Gill SAC
The adjoining Lough Gill SAC (Site Code: 001976) is of considerable importance for the
presence of four Red Data Book fish species that are listed on Annex II of the E.U. Habitats
Directive - Brook Lamprey (Lampetra planeri), River Lamprey (Lampetra fluviatilis), Sea
Lamprey (Petromyzon marinus) and Atlantic Salmon (Salmo salar). It is likely that the three
migratory species of these, salmon and river and sea lamprey, use the navigation channel
during migrations between the sea and the Lough Gill SAC. Timing of the works should take
these migrations into account and, despite the fact that the Lough Gill SAC will not be
directly impacted by the proposed dredging works, the link between freshwater and seawater
habitats and species should not be ignored.
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6.3
SUBTIDAL FLORA AND FAUNA – OFFSHORE DUMP SITE
This section describes the baseline surveys undertaken at the proposed offshore disposal
site, and presents an impact hypothesis for the predicted impacts of dumping the dredged
sediment at this location, based on the baseline data acquired at the site and the dumpsite
plume model and settlement pattern described in Chapter 11, “Coastal Processes”.
6.3.1 Introduction
The survey at the Sligo proposed dumpsite was conducted from the M/V Nomad, a multipurpose tug boat out of Killybegs, on two sampling dates, 27th January and 17th February
2011, covering both neap and spring tide conditions respectively. Following consultation
with The Marine Institute, it was recommended that the baseline study should involve a
hydrodynamic survey, benthic community study and sediment chemistry analysis. The
location of the proposed dump site is shown below in Figure 6.35.
Figure 6.35: Location of Proposed Offshore 1km² Dump Site
6.3.1.1 Hydrodynamic Survey
The hydrodynamic environment at the site was investigated by recording current speed and
direction, drogue movements and tidal elevations at various stages of the tide on both spring
and neap tidal conditions.
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6.3.1.2 Current and Tide Measurements
Current speed and direction was recorded mid water (45-50m) by means of an Aquadopp
current profiler every 10 minutes for an ebb and flood tide during both the neap (27th
January) and spring (17th February) tide. Tidal elevation was also recorded at the same
time. The meter was located on both occasions approximately in the centre of the site at 54°
35.800’ N, 9° 16.5879’ W on 27th January and 54° 36.0087’ N, 9° 16.5885’ W on 17th
February.
6.3.1.3 Drogue Studies
Drogues, designed to track currents at the surface, mid-water (45m) and off-bottom (90 m),
were released from the centre of the dump site at high water, mid-tide and low water and
tracked through to the following slack water when they were recovered on both sampling
dates. Each drogue was fitted with a GPS tracking unit set to record every 5 minutes, a
flashing beacon and a radar reflector for navigation alert and to aid recovery at night.
Regular checks were made on their progress by means of a DGPS unit as a backup to track
their progress and also aid recovery in this environment. Wind speed and direction was
regularly checked by means of a hand held anemometer.
6.3.1.4 Sediment Sampling
Sediment samples were taken at the locations outlined in Figure 6.36 and Table 6.1 by
means of a 0.1 m2 Day grab. It was intended to take a single grab at three stations along the
southwest-north east axis of the dumpsite and a fourth approximately 1 km from the
dumpsite in the direction opposite to the residual current for sediment analysis. However, on
site, the bottom type dictated where it was possible to take these grabs, which returned the
locations as outlined in Figure 6.36. When samples were returned from each station, notes
were logged on sediment type, amount, colour, smell and any other information that was
considered relevant. A sample of surface sediment was taken from the centre of the grab
and placed in a suitable cleaned container. All sampling jars were marked externally with
date, station number, sample number and survey reference number and placed in a cooler
box.
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Figure 6.36: Sampled stations at proposed dump site, Donegal Bay, Jan/Feb 2011
Table 6.10: Locations of the sediment sampling stations in Donegal Bay.
STATION
EASTING
NORTHING
St 1
117396
373288
St 2
116900
373170
St 3
117260
372202
St 4
116322
371258
On return to the laboratory, the samples for contaminant samples were sent to the UK
Environment Agencies National Laboratory Service (NLS) facility at Llanelli for the following
analysis:
Sample 1 - a), b), c), d), e), f) & g)
Sample 2 & 3 - a), b) & c)
Sample 4 - a), b), c), d), e), f) & g)
Where:
a) total organic carbon
b) carbonate
c) mercury, arsenic, cadmium, copper, lead, zinc, chromium, nickel, lithium,
aluminium.
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d) organochlorines including Ȗ-HCH (Lindane), and PCBs (to be reported as the 7 individual
CB congeners: 28, 52, 101, 118, 138, 153, 180).
e) total extractable hydrocarbons.
f) tributyltin (TBT) and dibutyltin (DBT)
g) Polycyclic aromatic hydrocarbons (PAH) - Acenaphthene, Acenaphthylene, Anthracene,
Benzo (a) anthracene, Benzo (a) pyrene, Benzo (b) fluoranthene, Benzo (ghi) perylene,
Benzo (k) fluoranthene, Chrysene, Dibenz (a,h) anthracene, Flourene, Fluoranthene,
Indeno 1,2,3 – cd pyrene, Naphthalene, Phenanthrene, Pyrene.
The methodologies for each of the analysis are included in the results report sent by NLS
and included as Appendix 8. Appropriate marine Certified Reference Material (CRM) were
analysed with the samples and the results presented with the sample results.
Granulometric analysis was carried out on one aliquot of each sediment sample as
described by Folk (1974). A 30-ml solution of aqueous sodium hexametaphosphate (6.2 g/l)
was added to 100 g of oven-dried (100°C) sediment; the mixture was made up to 1 litre with
distilled water, stirred mechanically for 15 min and allowed to stand overnight. This mixture
was then re-stirred and washed through a 45-ȝm sieve. This material left on the sieve was
oven-dried at 100°C and weighed, and the 45-ȝm fraction determined by subtraction. The
dried remaining fraction was broken up with a mortar and pestle and graded through a nest
of sieves of 4, 2, 1 mm and 500-, 250-, 125-, and 63-ȝm mesh. Each grade was weighed
and the value expressed as a percentage of the total dry weight of the sample. Material
passing through the 63 ȝm mesh was added to the 45-ȝm fraction and classified as the silt–
clay fraction. Water content was taken as the percentage weight difference between the wet
and dried sediment.
6.3.1.5 Benthic Communities
6.3.1.5.1
Faunal Samples
AQUAFACT has in-house standard operational procedures for benthic sampling and these
were followed for this project. A 0.1m2 Day grab was used to sample the grab stations. The
grab was weighted at 70–100 kg for sandy sediments. On arrival at each prescribed
sampling station, the vessel location was recorded using DGPS (Lat/Long & ING). Additional
information such as date, time, site name, sample code, depth, sampler, anchorage,
weather, sea state and exposure were recorded in a data sheet.
As for the sediment grabs, bottom type dictated the locations where grabs could be taken.
A minimum of three grab samples were taken at four faunal grab locations for faunal content
(Figure 6.37). The grab deployment and recovery rates did not exceed 1 metre/sec and <0.5
m/sec for the last 10m. Upon retrieval of the grab, penetration depth was measured and only
grab samples that contained a depth of >7cm for sand and >10cm for mud were retained.
Re-sampling occurred until a sufficient depth of sediment was collected in the grab (the
vessel repositioned between grab samples). All additional relevant data (sediment type,
texture, grain size, colour, odour, layering, volume, presence of fauna, algae, surface
features) were recorded in the sample data sheets.
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Figure 6.37: Locations of Faunal Stations, Donegal Bay, Jan/Feb 2011
The grab sampler was cleaned between stations to prevent cross contamination.
The contents of the grab sample were carefully and gently sieved on a 1mm mesh sieve as
a sediment water suspension for the retention of fauna. Great care was taken during the
sieving process in order to minimise damage to taxa such as spionids, scale worms,
phyllodocids and amphipods. The sample residue was carefully flushed into a pre-labelled
(internally and externally) container from below. Each label contained the sample code and
date. The samples were stained immediately with Eosin-briebrich scarlet and fixed
immediately in with 4% w/v buffered formaldehyde solution. These samples were ultimately
preserved in 70% alcohol upon return to the laboratory.
All faunal samples were placed in an illuminated shallow white tray and sorted first by eye to
remove large specimens and then sorted under a stereo microscope (x 10 magnification).
Following the removal of larger specimens, the samples were placed into Petri dishes,
approximately one half teaspoon at a time and sorted using a binocular microscope at x25
magnification. A full species list is presented in Appendix 4F on the accompanying data
DVD-ROM.
The fauna was sorted into four main groups: Polychaeta, Mollusca, Crustacea and others.
The ‘others’ group consisted of echinoderms, nematodes, nemerteans, cnidarians and other
lesser phyla. The fauna were maintained in stabilised 70% industrial methylated spirit (IMS)
6-53
following retrieval and identified to species level where practical using a binocular
microscope, a compound microscope and all relevant taxonomic keys.
6.3.1.5.2
Statistical Analysis
All replicates for each station were combined to give a total abundance for each station prior
to analyses. A data matrix of all the combined faunal abundance data was compiled and
used for statistical analyses. The faunal analysis was carried out using PRIMER ®
(Plymouth Routines in Multivariate Ecological Research).
Univariate statistics in the form of diversity indices were calculated on the combined replicate
data. The following diversity indices were calculated:
1) Margalef’s species richness index (D), (Margalef, 1958).
D
S 1
log2 N
where: N is the number of individuals
S is the number of species
2) Pielou’s Evenness index (J), (Pielou, 1977).
H' (observed)
J=
H'max
'
where: H max is the maximum possible diversity, which could be achieved if all species were
equally abundant (= log2S)
3) Shannon-Wiener diversity index (H'), (Pielou, 1977).
S
H ' = - ¦ i=1 p i (log 2 pi )
where: pI is the proportion of the total count accounted for by the ith taxa
Species richness is a measure of the total number of species present for a given number of
individuals. Evenness is a measure of how evenly the individuals are distributed among
different species. The diversity index incorporates both of these parameters. Richness
ranges from 0 (low richness) to 12 (high richness), evenness ranges from 0 (low evenness)
to 1 (high evenness), diversity ranges from 0 (low diversity) to 5 (high diversity).
The PRIMER ® manual (Clarke & Warwick, 2001) was used to carry out multivariate
analyses on the station-by-station faunal data. It must be noted here that the species that
were present only once or twice in the survey were excluded from the multivariate analysis.
All species/abundance data were fourth root transformed and used to prepare a Bray-Curtis
similarity matrix in PRIMER®. The fourth root transformation was used in order to downweigh the importance of the highly abundant species and allow the mid-range and rarer
species to play a part in the similarity calculation. The similarity matrix was then used in
classification/cluster analysis. The aim of this analysis was to find “natural groupings’ of
samples, i.e. samples within a group that are more similar to each other, than they are
similar to samples in different groups (Clarke & Warwick, loc. cit.). The PRIMER ®
programme CLUSTER carried out this analysis by successively fusing the samples into
6-54
groups and the groups into larger clusters, beginning with the highest mutual similarities then
gradually reducing the similarity level at which groups are formed. The result is represented
graphically in a dendrogram, the x-axis representing the full set of samples and the y-axis
representing similarity levels at which two samples/groups are said to have fused. The
CLUSTER programme was set to include a series of ‘similarity profile’ (SIMPROF)
permutation tests, which look for statistical evidence of genuine clusters in samples which
are a priori unstructured. SIMPROF performs tests at every node of a completed
dendrogram, that the group being sub-divided has ‘significant’ internal structure. The test
results are displayed in a colour convention on the dendrogram plot (samples connected by
red lines cannot be significantly differentiated).
The Bray-Curtis similarity matrix was also subjected to a non-metric multi-dimensional
scaling (MDS) algorithm (Kruskall & Wish, 1978), using the PRIMER ® program MDS. This
programme produces an ordination, which is a map of the samples in two- or threedimensions, whereby the placement of samples reflects the similarity of their biological
communities rather than their simple geographical location (Clarke & Warwick, 2001). With
regard to stress values, they give an indication of how well the multi-dimensional similarity
matrix is represented by the two-dimensional plot. They are calculated by comparing the
interpoint distances in the similarity matrix with the corresponding interpoint distances on the
2-d plot. Perfect or near perfect matches are rare in field data, especially in the absence of a
single overriding forcing factor such as an organic enrichment gradient. Stress values
increase not only with the reducing dimensionality (lack of clear forcing structure), but also
with increasing quantity of data (it is a sum of the squares type regression coefficient).
Clarke and Warwick (loc. cit.) have provided a classification of the reliability of MDS plots
based on stress values, having compiled simulation studies of stress value behaviour and
archived empirical data. This classification generally holds well for 2-d ordinations of the type
used in this study. Their classification is given below:
x
x
x
x
Stress value < 0.05: Excellent representation of the data with no prospect of
misinterpretation.
Stress value < 0.10: Good representation, no real prospect of misinterpretation of
overall structure, but very fine detail may be misleading in compact subgroups.
Stress value < 0.20: This provides a useful 2-d picture, but detail may be
misinterpreted particularly nearing 0.20. Stress value 0.20 to 0.30: This should be
viewed with scepticism, particularly in the upper part of the range, and discarded for a
small to moderate number of points such as < 50.
Stress values > 0.30: The data points are close to being randomly distributed in the 2d ordination and not representative of the underlying similarity matrix.
Each stress value must be interpreted both in terms of its absolute value and the number of
data points. In the case of this study, the moderate number of data points indicates that the
stress value can be interpreted more or less directly. While the above classification is
arbitrary, it does provide a framework that has proved effective in this type of analysis.
6-55
SIMPER analysis was then carried out on the transformed data to determine the
dominant/characterising species within each group identified by the CLUSTER/SIMPROF
analysis. These results are presented in Appendix 4H.
6.3.1.5.3
Video Survey
Video footage of the seafloor and associated biota was recorded by means of a LH Camera
professional colour video camera that was operated from the work vessel. Footage was
recorded directly to a laptop for later analysis. Video transects were attempted at various
locations across and outside the dumpsite in order to get footage of the various bottom types
encountered at this location. However a significant swell and boat drift due to the moderate
to strong wind hampered this operation. In total 6 video transects were achieved across the
area during the January survey as indicated in Figure 6.38. Additional video transects were
attempted during the February survey. However, the camera was damaged on the first
transect attempted on the 17th February and no footage was recorded.
374000
373500
V2
V1
373000
V3
V4
372500
V6
372000
371500
V5
371000
116000
116500
117000
117500
118000
118500
119000
Figure 6.38: Video transect locations in the vicinity of the proposed dumpsite,
Donegal Bay, January 2011.
6.3.2 Results
6.3.2.1 Hydrodynamic Survey
6.3.2.1.1
Current and Tide measurements
Figure 6.39 presents current (stick plots) and tide measurements from the dump site location
on both a neap (27th January) and spring (17th February) tide.
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Figure 6.39 Current and tide measurements, Donegal Bay, Jan & Feb 2011.
The tidal range recorded during the neap was 2.0 m while the range during the spring was
3.0 m. Current velocities were relatively low with a maximum velocity of 0.15ms-1 recorded
during the neap and 0.217 ms-1 recorded during the spring tide. Due to the low velocities
recorded during the neap tide, the direction of the water movement was difficult to assess
although in general, it was in a north west direction during the ebb tide and south east during
the flood (see stick plot, Figure 6.39). With the increased velocities during the spring tide,
the direction of water movement was more defined with an easterly current during the flood
and west flow during the ebb.
6.3.2.2 Drogue Study
6.3.2.2.1
Neap Tide (27.1.2011)
Track records of the drogues released on the ebb and flood tide on 27.1.2011 are presented
in Figure 6.40 and Figure 6.41, respectively, and the track data included as Appendix 4E on
the accompanying DVD along with the current measurements as detailed in the previous
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section. Mid-water and off-bottom drogues, released at the same time, remained close to
each other while the surface drogue followed a different path. This was mainly due to the
prevalent wind, which was predominantly easterly in direction and increased from
approximately 3 ms-1 at the start of the study to 5 ms-1 towards the end of the study. This
was particularly evident during the flood tide deployments when the mid-water and offbottom drogues moved in a south-east direction following water movement as recorded by
the current meter (see Figure 6.39) while the surface drogues moved in the opposite
direction in a north-westerly direction under the influence of the 4-5 ms-1 north-westerly wind
(Figure 6.41). The average speed of the surface drogue (Drop 1) over the full ebb tide was
0.39 km/h while the mid-water and off-bottom drogues recorded average speeds of 0.34
km/h and 0.33 km/h, respectively. This compared to average speeds of 0.15 km/h for the
surface drogue and approximately 0.1 km/h for the mid water and off-bottom drogues.
375000
Drogue Drop 1 - 11:15
Recovery - 18:00
Wind 3-4 m/s
374500
High Water 11:40
Low Water 18:00
374000
373500
373000
372500
Surf ace
372000
116000
116500
M id-wat er
Of f -bot t om
117000
D
Surf ace 2
117500
M idwat er 2
118000
Figure 6.40 Ebb drogue tracks, Donegal Bay, 27.1.2011
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118500
Of f -bot tom 2
119000
375000
Recovery - 22:00
Wind 4-5 m/s
374500
High Water 11:40
Low Water 18:00
374000
373500
373000
372500
Surf ace
Surf ace 2
372000
116000
116500
M id-water
M idwat er 2
117000
Of f -bott om
Of f -bott om 2
117500
118000
D
118500
119000
Figure 6.41: Flood drogue tracks, Donegal Bay, 27.1.2011
6.3.2.2.2
Spring Tide (17.2.2011)
Track records of the drogues released on the ebb and flood tide on 17.2.2011 are presented
in Figure 6.42 and Figure 6.43, respectively, and the track data included in Appendix 4F. The
gps track of the off-bottom drogue released on the flood tide and drop 4 on the ebb tide was
found to be corrupted and could not be used in the Figures. However, as noted in the neap
tide study, the mid-water and off-bottom drogues, released at the same time, remained close
to each other during the spring tide study and the mid-water track is representative of both.
Unlike the neap study, the prevailing wind (2-5 ms-1 south easterly) did not have the same
influence on the drogue tracks.
The average speed of the surface drogue (drop 1) over the full flood tide was 0.4 km/h while
the mid-water and off-bottom drogues recorded average speeds of 0.36 km/h. This
compared to average speeds of 0.69 km/h for the surface drogue and 0.57 km/h and 0.51
km/h for the mid water and off-bottom drogues, respectively.
6-59
376000
375500
Recove ry - 17:15
Wind 2-3 m /s
Low Water 11:00
High Water 17:10
Low Water 23:00
Range 3 m
375000
374500
374000
373500
373000
372500
Surface
372000
116000
116500
M id-water
117000
Off-bottom
117500
D
118000
Surface 2
118500
M idwater 2
119000
Of f-bottom 2
119500
120000
Figure 6.42 Flood drogue tracks, Donegal Bay, 17.2.2011
376000
Recovery - 23:00
375500
Wind 4-5 m /s
Low Water 11:00
High Water 17:10
Low Water 23:00
Range 3 m
375000
374500
374000
373500
373000
372500
372000
114500
Surface
M id-water
115000
115500
Off-bottom
116000
D
116500
Surface 2
117000
M idwater 2
117500
Off-bottom 2
118000
Figure 6.43 Ebb drogue tracks, Donegal Bay, 17.2.2011
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118500
6.3.2.3 Sediment Samples
The detailed report of the granulometric and chemical composition of the sediment samples
recovered from the proposed dump site is reported in Section 10.4.2 of Chapter 10,
“Geology”.
In general, the sediments collected in and around the dumpsite (Stations 1-3) were typically
made up of fine sand with varying amounts of coarse sand and gravel. This corresponds
well with the properties of the sediment to be dredged. The sediments were also subjected
to chemical testing under the supervision of the Marine Institute as per the requirements of
the Dumping at Sea Acts 1996-2006 (as amended 2009) and these results are also
presented in that chapter.
6.3.2.4 Benthic Communities
The taxonomic identification of the benthic infauna across all 4 stations sampled in Donegal
Bay yielded a total count of 77 taxa accounting for 262 individuals, ascribed to 8 phyla. A
complete listing of the taxa abundance is provided as Appendix 4F, which is on the
accompanying data DVD.
Of the 77 taxa enumerated, 43 were annelida (segmented worms), 11 were crustaceans
(crabs, shrimps, prawns), 14 were molluscs (mussels, cockles, snails etc.), 4 were
echinoderms (starfish, brittlestars, sea cucumbers), 2 were cnidarians (corals, jellyfish etc), 1
was aphoronid (horseshoe worm), 1 was a nematode (round worm) and 1 was a nemertean
(ribbon worm).
6.3.2.4.1
Univariate Analysis
Univariate statistical analyses were carried out on the combined replicate station-by-station
faunal data. The following parameters were calculated and can be seen in Table 6.11; taxon
numbers, number of individuals, richness, evenness and diversity. Taxon numbers ranged
from 19 (Station 2) to 41 (Station 4). Number of individuals ranged from 29 (Station 2) to 81
(Station 1). Richness ranged from 5.35 (Station 2) to 9.29 (Station 4). Evenness ranged from
0.92 (Stations 1 and 3) to 0.95 (Stations 2 and 4). Diversity ranged from 4.02 (Station 2) to
5.10 (Station 4).
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Table 6.11 Diversity indices for the 4 stations sampled in Donegal Bay
Station
Station 1
Station 2
Station 3
Station 4
6.3.2.4.2
No. Taxa
31
19
32
41
No. Individuals
81
29
79
74
Richness
6.83
5.35
7.09
9.29
Evenness
0.92
0.95
0.92
0.95
Diversity
4.53
4.02
4.58
5.10
Multivariate Analysis
The dendrogram and the MDS plot can be seen in Figure 6.44 and Figure 6.45 respectively.
SIMPROF analysis revealed that there was no significant difference between the 4 stations
(hence the red line joining all stations in the dendrogram).
Faunal returns from the area in question were poor, with the maximum number of any taxon
present at a station being 11 (the cnidarians Edwardsiidae sp. at Station1). Edwardsiidae sp.
was also the dominant taxon at the other 2 stations located within the dumpsite (Stations 2
and 3). Of the 31 taxa found at Station 1, 19 were present twice or less, of the 19 taxa found
at Station 2, 17 were present twice or less and of the 32 taxa found at station 3, 19 were
present twice or less.
Station 1 was dominated by Edwardsiidae sp., the polychaete Chaetozone setosa, the
polychaete Aonides oxycephala and the mollusc Thyasira flexuosa. Station 2 was dominated
by Edwardsiidae sp. and the polychaete Scoloplos armiger. Station 3 was dominated by
Edwardsiidae sp., Thyasira flexuosa, Chaetozone setosa and Scoloplos armiger.
The control station (Station 4) contained the highest number of taxa (41) and of those 29
were present twice or less. Station 4 was dominated by the polychaete Chaetozone setosa,
the enchinoderm Echinocyamus pusillus, the polychaete Lumbrineris cf cingulata and the
cnidarians Edwardsiidae sp.
SIMPER analysis revealed that the taxa responsible for the grouping of all stations as one
group were Edwardsiidae sp., Harpinia sp., and the polychaete Owenia fusiformis. Appendix
4H contains the results of the SIMPER analysis.
6-62
Figure 6.44 Dendrogram showing the natural grouping of each station sampled in
Donegal Bay.
The MDS plot reflects the data in the dendrogram. The stress value of the MDS ordination is
0; which results in a good representation with no real prospect of misinterpretation of the
overall structure, but the very fine detail may be misleading in compact subgroups.
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Figure 6.45: MDS plot of all stations sampled in Donegal Bay.
6.3.2.4.3
Video Survey
Footage from each of the video transects (see Figure 6.38) are included as Appendix 4G on
the DVD accompanying this report. It is noticeable that the seafloor is very variable with
bottom type quickly changing composition across each transect indicating a mosaic of
bottom types in the area. A summary of these features are included as Table 6.12. The
seafloor along video transect 6 was similar to that seen in video transect 5. However, due to
a power loss during recording of V6, the footage was lost and no images or recording is
available for this transect.
Faunal presence across the transects was sparse, the only obvious biota noted during the
transects being a number of starfish, Asterias rubens, and hydroid colonies (sp. ident.) and
serpulids on the boulders.
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Table 6.12 Descriptions of the video transects, Donegal Bay, January 2011.
V1
Start 118018 E, 373358 N
End 118089 E, 373229 N
Transect length - 147 m
Clean gravel formed in large waves,
fine sand in small waves to bolder field
V2
Start 117818 E, 373351 N
End 117979 E, 373307 N
Gravel with mud mix,
fine sand in small waves
6-65
V3
Start 117760 E, 373031 N
End 117912 E, 372883 N
Boulder field with varying amounts of silt,
sand and gravel. A single starfish, Asterias
rubens,
was imaged.
V4
Start 117298 E, 372791 N
End 117486 E, 372716 N
Fine sand formed into small waves
6-66
V5 & V6
Start 117352 E, 372791 N
End 117094 E, 372136 N
Clean gravel formed in large waves,
fine sand in small waves to bolder field and
combinations each.
6.3.3 Proposed Dumpsite Baseline Conditions - Conclusions
Current velocities were relatively low at the site with a maximum velocity of 0.15ms-1
recorded during neap and 0.217 ms-1 recorded during spring tides. In general, water
6-67
movement was in a north west to west direction during the ebb tide and south east to east
direction during the flood. The tidal range recorded during the neap was 2.0 m while the
range during the spring was 3.0 m.
The track taken by drogues designed to follow water movement at different depths agreed
with the direct current measurements with movement in a north west to west direction during
the ebb tide and south east to east direction during the flood. Given the relatively low
current velocities, wind speed and direction had a major influence on drogue movement.
The marine sediments collected in and around the potential dumpsite were typically made up
of fine sand with varying amounts of coarse sand and gravel. The sediments were typically
brown or grey/brown in colour with no particular smell.
In general, contaminant analysis of sediments taken from the four stations indicated that the
marine sediments present at the dump site do not contain significant levels of contaminants
and are within the guideline values for marine sediments from similar environments as
proposed by The Marine Institute. However, copper levels at Stations 1, 2 & 3 and
chromium and nickel at Station 3 were above the upper level guidance values as published
by The Marine Institute (2006). The upper level guidance values are set at the lower end of
the known range of effective concentrations i.e. lowest concentrations shown to have
adverse effects on marine organisms. There are no obvious nearby sources of any potential
source for elevated levels (e.g. a shipwreck) within the sampling area and it has never been
previously used as a dump site.
The Marine Institute was consulted in relation to the elevated copper, chromium and nickel
levels and the sampling laboratory, NLS, was asked to verify that the analysis was
undertaken correctly. The laboratory has confirmed that the sampling was undertaken
correctly and the results are accurate. As of June 2012 the Marine Institute are continuing
their investigation into the sampling process undertaken at the laboratory to verify whether
these results are correct.
The sediment samples obtained at the offshore disposal site are required as part of the
dumping at sea licensing process to characterise the baseline of the sediments at the dump
site. The nickel, copper and chromium levels measured in the sediment to be dredged are
all substantially below the lower guidance level. All the other parameters tested in the
dredged sediments are also below the Marine Institute’s guidance levels and the sediment is
therefore confirmed as being clean and will pose no significant adverse impacts in terms of
sediment chemistry at the dump site.
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6.3.4 Predicted Impacts at the Proposed Offshore Dump Site
dumping operation on sedimentation and suspended sediment loads in the area of the
proposed dumpsite (see relevant section of model details). Results from the model
simulation reported that:
x
x
x
x
the suspended sediment values beyond the immediate vicinity of the dumping
operation are minimal.
the majority of the dumped material will be deposited and remain within 2km on the
dumping site with only a small amount of material being transported further offshore by
the residual current.
material at the bed may be re-suspended however any subsequent transport will take
place by advection on tidal currents. In the area of the dump site the tidal currents are
weak and the material would not be transported significant distance before the current
speeds reduce at slack water and the material is deposited, or if it remains in
suspension it will be carried back to the site on the returning tide.
Based on the results of the hydrodynamic modelling study, the final settlement model
(Figure 11. 58 in Chapter 11) shows that most of the dumped sediment will settle on
the seabed close to the dump site. Some of the material will migrate towards the east
under the influence of tidal action, but all particles will settle within 5.5km of the dump
site. An area extending across approximately 2km to the east and south of the
dumpsite will experience deposition in excess of 20mm. Within this, an area
measuring approximately 0.5km² will experience deposition depths in excess of
130mm. It can be seen from the suspended sediment and deposition diagrams that
the proposed dredging will not have a significant impact on bed sediments or water
quality in a waters beyond the immediate vicinity of the dumping site. Sediment
transport due to wave action is likely to be limited at the site due to the 90m water
depth. In addition any material that may be re-suspended during extreme swell events
will not be transported far from the site due to the weak tidal currents.
Potential impacts resulting from dumping the dredge spoil at the proposed dumpsite are
discussed below.
6.3.4.1 Bottom Communities
Bottom type and associated species composition in the vicinity of the dumpsite was very
variable over such a small sampling area. Following dumping, all species covered by the
dumped material will be lost. However, it was found that no unusual species or habitats
were located within the proposed dump area and given the relatively small area of impact
relative to the surrounding habitats, there should be no significant negative impact on the
bottom communities from Donegal Bay.
Responses of benthic infauna to large scale disturbance by dredged material placement
have been studied at numerous sites. Wilber et al (2008) monitored eight paired (placement
and reference) areas in Corpus Christi Bay, Texas in 1995 and 1996. Total infaunal
abundance, taxa richness, and the biomass of annelids and molluscs in placement areas no
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longer differed from that of reference areas approximately one year after placement.
Differences in community structure between placement and reference areas returned to preplacement levels one year after disturbance. The use of the term “recovery” with reference to
recolonisation of dredging-related disturbance implies a return to pre-placement ecological
conditions that are frequently neither a reality nor a practical expectation for areas that are
subject to repeated disturbances. Wilber et al (Loc. cit.) characterisation of biological
responses to dredged material disturbance targeted benchmarks that were linked to both
pre-disturbance conditions and differences between disturbed and neighbouring undisturbed
areas and indicate that impacts persisted less than one year. However, Wilber and Clarke
(2008) point out that few generalisations can be made about typical recovery rates because
biological responses are influenced by numerous factors, including site-specific bathymetry,
hydrodynamics, depth of deposited material, the spatial scale of the disturbance, sediment
type and timing and frequency of the disturbance. That being said, it is probable that
following completion of the dumping operation, the impacted seafloor will be recolonised
from the surrounding faunal community and will integrate as part of the overall habitat.
6.3.4.2 Fish and Crustaceans
Suspended solids in the area will be temporarily increased during the dumping phase and
the seafloor in the footprint of the dumped material will be smothered with the loss of burrow
habitat for shrimp and food source for bottom feeding fish.
Local fishing interests have been concerned that the dumping of dredged spoil could
negatively impact on the crab, lobster and prawn fishery. Given the relatively small footprint
of the dumped material, the immediate loss of habitat to crustaceans is negligible and long
term, could increase available soft sediment for burrowing. Results from the video survey
(see Video Survey Section 6.3.1.5.3) would suggest that the predominant bottom type at the
dumpsite of mixed gravel, boulders and sand is typical crab ground but unsuitable for
Nephrops, which require soft substrate for burrowing, or lobster, which are normally found on
rock that provides shelter. Burrows or individuals were not imaged in any of the video
transects recorded in the vicinity of the dumpsite.
Dumping on the proposed dumpsite has the potential to kill a number of commercial
crustaceans although most will escape. Those that escape undamaged will quickly
recolonise the surrounding seabed and migrate to new habitats if necessary. Shelton (1973)
reported that Cancer pagurus avoided areas of spoil dumping and suggested this may be
due to increased suspended sediment or due to decreased macrofauna. Cancer pagurus
relies on visual acuity to find prey so although mortality due to an increase in suspended
sediment is unlikely, some perturbation is expected. The Marine Life Information Network
(MarLin.ac.uk) suggest that smothering is unlikely to cause mortality in crabs, which are able
to escape from under silt and migrate away from an area experience dumping. Given the
crabs normal behaviour for “pit digging” in soft sediments (Hall et al, 1991), it is unlikely that
any increase in fine sediment will have significant negative impacts on their health.
The turbidity caused by suspended solids can affect primary production by shading and
increased sedimentation can disturb benthic communities. There is also the possibility of
negative impact on shrimp, particularly if solids are suspended during the breeding season.
6-70
In an assessment of tolerance to suspended sediment, the Marine Life Information Network
(MarLin.ac.uk) assess Nephrops norvegicus as being probably tolerant of changes in
suspended sediment. This is based on the fact that Nephrops are not dependent on
increased suspended sediment for food availability as Nephrops is a carnivore and feeds by
predation and scavenging. The species is also able to move to more suitable conditions if
necessary. Therefore Nephrops has been assessed as tolerant to this factor. Nephrops
norvegicus is also assessed as being tolerant of displacement, such as that caused by a
passing trawl that does not kill the species but throws it into suspension, because it can
reburrow into suitable substrata. Following displacement to suitable sediments Nephrops
norvegicus are likely to commence burrowing immediately provided that individuals are not
damaged.
Newcombe and MacDonald (1991) state that high levels of suspended solids (typically of the
order of 20,000 mg/L or more for exposure periods of 24 to 96 hours for smolts of several
species) can be lethal for salmonids. The same authors also detail sub-lethal responses
(including cellular damage and physiological stress) and behavioural responses (e.g.
avoidance behaviour and alarm responses) to suspended solids. The concentrations of
suspended solids causing these responses were variable (from 6 to 650 mg/L for
behavioural responses and from 14 to 1547 mg/L for sub-lethal responses) and are probably
dependent on the duration of exposure of the fish to the suspended solids. Whitman et al.
(1992) observed the effects on Pacific Chinook Salmon (Oncorhynchus tshawytscha) that
were caused when volcanic ash was added to water under experimental conditions. When
ash was added to a concentration of 350 mg/L the preference of the fish for home water (i.e.
water from their natal river) was significantly reduced. This was apparently due to avoidance
of the ash, rather than an inability to identify home water.
The avoidance behaviour of Cod and Herring to dredging-induced turbidity and the effects of
sediment plumes on the buoyancy and mortality of Cod eggs and larvae have been studied
as part of the Environmental Impact Assessment for the Öresund Link bridge-tunnel project
between Denmark and Sweden (Westerberg et al., 1996). The avoidance threshold to
suspended sediments of glacial clay of limestone origin was studied in an experimental
saltwater flume and was found to be approximately 3 mg/l for both species. Adhering
particles from sediment suspensions were shown to cause a loss of buoyancy for Cod eggs,
while larvae showed increased mortality on exposure to sediment concentrations of 10 mg/l.
The adverse impacts of suspended solids of fish that have been recorded experimentally are
generally at concentrations greater than 10 mg/l and often several orders of magnitude more
than this. Results from the model sediment analysis predict that concentrations of
suspended material in the dredge plume will fall to concentration of 3.5 mg/l or less within
several hundred metres of the disposal site. It should be realized that negative impacts on
fish from experimental data often followed prolonged periods of exposure, whereas fish in
the vicinity of the site of the proposed development will have the opportunity to move away
from areas affected by the dredge plume. It is therefore concluded that there will be no
significant impact on fish species as a result of the dumping operation.
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6.3.5 Mitigation of the Potential Impacts at the Dump Site and Residual Impacts
Given that the material is required to be dumped only within the limits of the proposed
defined dumpsite, there are few mitigation measures that can be proposed to reduce the
impact of the material on the seafloor and short term effects on the water column as
predicted by the hydrodynamic model.
As the model predicts the fate of the material during slack water, optimum dumping to
reduce far field effects should occur at high or low water when water currents are at their
minimum to reduce dispersion of the material. However, given the relatively slack currents
recorded at the site (see Section 6.3.1.2 Current and Tide Measurements); this mitigation
measure would be limited in its effectiveness. Furthermore, as the dumpsite takes several
hours to steam to, it will not be possible to arrive on site at a defined stage of the tide.
The proposed dump site has endeavoured to mitigate against impacts through site selection
- it been chosen in an area where the residual currents will not transport sediment east into
Donegal Bay and does not occur in a known spawning area.
No unusual species or habitats were found within the proposed dump site during the video
and grab sampling studies. Given the relatively small area of impact relative to the
surrounding habitats, there should be no significant negative impact on the bottom
communities from Donegal Bay. Any areas affected by sedimentation will be quickly
recolonised upon completion of dumping. No significant impact is predicted to occur on fish
species as a result of the dumping operation.
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6.4
MARINE MAMMALS
This section of the Environmental Appraisal details the potential risks to marine mammals
and makes recommendations for mitigation measures related to the proposed dredging of
Sligo Harbour. It is based on a site visit by the author, information from published and
unpublished literature and communication with local relevant authorities. This report is
based on the information provided in Chapter 4.0 – “Project Description” which includes both
dredging and dumping activities.
6.4.1 Legislation pertaining to Marine Mammals in Irish waters
Marine mammals are protected by national legislation and by a number of international
regulations which the Republic of Ireland is signatory to. The main legislation that affords
protection to marine mammals in Irish waters is the Wildlife Act (1976) and the Wildlife
(Amendment) Act (2000), which prohibits wilful interference to wild mammals and
disturbance of resting and breeding sites.
All cetacean species (whales, dolphins and porpoises) occurring in European waters are
now afforded protection under the EC Habitats Directive. All cetaceans are included in
Annex IV of the Directive as species “in need of strict protection”. Additionally, the harbour
porpoise (Phocoena phocoena) and bottlenose dolphin (Tursiops truncatus) are designated
Annex II species (those animals of community interest, whose conservation requires the
designation of special areas of conservation). Ireland’s two pinniped (seals) species, the
Harbour Seal (Phoca vitulina) and Grey Seal (Halichoerus grypus) are also designated
Annex II species under the EC Habitats Directive.
The Republic of Ireland is also signatory to conservation orientated agreements under the
Bonn Convention on Migratory Species (1983), the OSPAR Convention for the Protection of
the Marine Environment of the northeast Atlantic (1992) and the Berne Convention on
Conservation of European Wildlife and Natural Habitats (1979).
In light of the legislation and conservation status of marine mammals, careful consideration
must be given during all anthropogenic activity with potential effect on the species and their
habitat.
Furthermore, Sligo Harbour holds a number of important environmental
designations including the Cummeen Strand Special Area of Conservation and the
Cummeen Strand/Drumcliff Bay Special Protection Area. Nearby Drumcliff Bay is also a
Special Area of Conservation. Therefore, the EIA requires an Appropriate Assessment
which will fulfil the requirements of the Habitats Directive.
6.4.2 Desktop Study of Marine Mammals in the Area
It is necessary to determine what marine mammals use the area and surrounding waters in
order to estimate the likely significance of any impacts resulting from the proposed
development.
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Figure 6.46 shows a map of cetacean sightings recorded by the members of the Irish Whale
and Dolphin Group and public sightings reported to the group in the sea around County Sligo
and Donegal between January 2010 and June 2012 (www.iwdg.ie). The map is a useful tool
in gaining a broad overview of the species that may occur in the area, however it is limited in
the sense that observations will mainly only occur from terrestrial vantage points and the
results may be skewed towards sightings from more populated places. The figure shows
that the species recorded in the Sligo Harbour area and adjacent areas are mainly dolphins
and harbour porpoises.
Figure 6.46: Cetacean sightings in the County Sligo area.
(All records are validated and available on www.iwdg.ie)
6.4.2.1 Cetaceans
Based on the species’ ecology and sighting records, cetacean species likely to use the area
include minke whales (Balaenoptera acutorostrata), harbour porpoises (Phocoena
phocoena) bottlenose dolphins (Tursiops truncatus), Risso’s dolphins (Grampus griseus)
and common dolphins (Delphinus delphis) (Evans, 1992, Berrow et al., 2001; Ingram, 2000;
Ingram et al., 2001 and 2003; Rogan et al., 2001; Ó Cadhla et al., 2004; O Brien et al., 2009;
Anderwald et al., 2011).
Minke Whale
The most common species of baleen whale found around Irish coasts, the minke whale is
frequently recorded around all parts of the west coast (Pollock et al., 1997, Berrow et al.,
2002; Ó Cadhla et al., 2004). Research conducted in UK waters suggest that the species
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moves southwards to inshore Atlantic Margin waters in spring and summer remaining until
late autumn following which numbers decline (Pollack et al., 2000; Northridge et al., 1995).
The minke whale has been sighted in near inshore waters in northwest, west and southwest
Ireland (Ó Cadhla et al., 2004; Roycroft et al., 2007) and of all whale species that use Irish
waters is the species with the most near-shore distribution, and therefore potentially the
most vulnerable to anthropogenic noise resulting from coastal developments such as the
proposed harbour works. It is unlikely, however, that there is a threat to individuals from the
proposed dredging, as there are no records of this species within Sligo Harbour and
therefore highly unlikely that the dredging work will impact on this species. Minke whales
have been sighted in Donegal Bay (IWDG, 2011) and it is likely they use the proposed
dumping area. Mitigation measures outlined in Section 6.4.8 will minimise potential impacts
of the proposed works if there is occasional use of the harbour by this species.
Vocalisations of minke whales involve intense, low frequency, broadband (0.5-1 kHz
bandwidth) and harmonic down-sweeps with maximum source level of 165 dB re 1 IPa
(Edds, 1988).
Harbour Porpoise
Sightings of Europe’s smallest cetacean species, the harbour porpoise, have been relatively
common off all coasts of Ireland and in the Irish Sea (Northridge et al., 1995; Hammond et
al., 1995; Pollack et al., 1997; Berrow et al., 2001; Ó Cadhla et al., 2004; Anderwald et al.,
2011). The small size of harbour porpoises and their erratic surfacing behaviour make them
difficult to detect. Information relating to the movements of this species around coastal
areas is very limited but there have been occasional sightings of the species within Sligo Bay
(IWDG, 2011) and this species is likely to visit Sligo Harbour particularly at mid-high water.
It is also likely that they will use the proposed dump area west of Donegal Bay.
Harbour porpoises produce high-frequency sounds used for echolocation and
communication, but do not make frequency-modulated whistles typical of many delphinids.
The high frequency sounds are comprised entirely of click trains, produced in two narrow
band frequency components, one between 1-20 kHz and the other between 120-160 kHz
(peaking around 125-130 kHz) (Goodson et al., 1995). Maximum source level is estimated at
between 149 and 177 dB re 1IPa at 1 m (Akamatsu et al., 1992).
Harbour porpoises are very sensitive to vessel noise and activity and are unlikely to
approach areas of high activity and are therefore considered not likely to be impacted by the
proposed works. However, mitigation measures outlined in Section 6.4.8 will minimise
potential impacts of the proposed works if there is occasional use of the harbour by this
species.
Bottlenose Dolphin
A coastal species of cetacean commonly sighted in western Irish waters (Evans, 1992,
Pollock et al., 1997) bottlenose dolphins are numerous on the south and west coasts
(Ingram and Rogan, 2003; Ingram et al., 2001, 2003). There are resident communities in the
waters of the outer Shannon Estuary (Ingram, 2000; Ingram and Rogan, 2003) and a
transient population recorded off all Irish coasts (O Brien et al., 2009). Bottlenose dolphins
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have been recorded in the Sligo Harbour area and likely to be part of this transient
population. Bottlenose dolphins are a wide-ranging species and individuals commonly travel
between coastal regions especially during the summer months (Ingram et al., 2003).
The bottlenose dolphin makes a wide range of vocalisations. Echolocation clicks (used for
orientation and foraging) are composed of intense short duration broadband clicks (40-130
kHz) (Au, 1993). Burst pulse vocalisations may have a variety of social functions (0.2-16
kHz). Whistles are pure tone frequency modulated calls ranging from 2-20 kHz. Clicks and
whistle vocalisations can be made simultaneously.
Bottlenose dolphins may be attracted to vessel activity, making them potentially vulnerable
to physical harm from industrial activities. It is considered unlikely that the proposed works
will impact upon bottlenose dolphins in the area as they do not frequent the waters of the
inner harbour, however mitigation measures outlined in Section 6.4.8 will minimise potential
impacts of the proposed works if there is occasional use of the harbour by this species.
Common Dolphin
Although a mainly oceanic species, common dolphins have been frequently observed in
large schools around the coasts of Ireland (Pollock et al., 1997; Gordon et al., 2000) and it is
the most commonly stranded cetacean around the Irish coast (Berrow & Rogan, 1997). The
mobile schools of common dolphins seen in coastal waters tend to be foraging for shoaling
fish species.
Vocalisations of common dolphins vary from whistles of 1-50 kHz frequency (mainly 6-12
kHz, max. source level 172dB) to echolocation clicks which may reach 150 kHz (max.
source levels 170 dB) (Evans, 1973; Moore & Ridgway, 1995). Clicks and whistles may be
given simultaneously.
Common dolphins are attracted to vessels and are easily sighted and identified. It is
considered unlikely that the proposed dredging works will impact upon common dolphins in
the area as they do not frequent the waters of the harbour; however it is possible they will
use the area where the proposed dumping of dredged material will take place. Mitigation
measures outlined in Section 6.4.8 will minimise potential impacts of the proposed works on
this species.
Risso’s Dolphin
In Ireland Risso’s dolphin have generally been recorded close to the coast with highest
numbers of sightings between August and February (Pollack et al., 1997; 2000). A large and
robust species, Risso’s dolphins are slow moving and often seen in small schools around the
west coast (Berrow et al., 2002). Risso’s dolphins will not usually approach vessels but are
readily recognised by their distinctive colouration patterns and large size.
Vocalisations include a variety of clicks, whistles, and pulsed calls. Whistles are rarely
heard, but range over 2.5-20 kHz, maximum source level of 170 dB re 1IPa @ 1 m. Clicks
have peak frequency at 65 kHz and durations of 40-100 secs (Au, 1993).
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It is considered unlikely that the proposed works will impact upon this species as there are
no records of this species in the harbour or surrounding area, however mitigation measures
outlined in Section 6.4.8 will minimise potential impacts of the proposed works if there is
occasional use of the harbour by this species.
6.4.2.2 Pinnipeds
Harbour Seal
Harbour Seals (also known as “Common Seals”) have established themselves at terrestrial
colonies (or haul-outs) along all coastlines of Ireland, which they leave when foraging or
moving between areas, for example, and to which they return to rest ashore, rear young,
engage in social activity, etc. These haul-out groups of harbour seals have tended
historically to be found among inshore bays and islands, coves and estuaries (Lockley,
1966; Summers et al., 1980), particularly around the hours of lowest tide. Harbour seals
haul-out at terrestrial haul-out sites on the Aran Islands. A national aerial census of harbour
seals in Ireland during 2003 identified haul-out sites in Ballysadare Bay Co. Sligo where over
250 harbour seals were recorded and in Killala Bay where approximately 110 seals were
recorded (Cronin et al., 2004, 2007). These counts, which are conducted during the seals
annual moult are considered to represent about 60-70% of the total number of seals using
the area. Therefore there are approximately 500-600 harbour seals using haul-out sites
within 40km of Sligo harbour, assuming the population has not changed since the 2003
census. Recent findings from tagging harbour seals in SW Ireland suggest that harbour
seals are local foragers, generally staying within 20km of their haul-out sites (Cronin et al.,
2008). It is highly likely that harbour seals from haul-out sites in Ballysadare Bay use the
waters of Sligo Harbour.
Harbour seals are most vulnerable at their terrestrial haul-out sites during breeding and
moulting periods. These events occur between June and September in Ireland. However
the terrestrial haul-out sites in the Ballysadare area are not located in close proximity to Sligo
Harbour and therefore there is no considered threat of physical disturbance at the haul-out
sites by the proposed works.
In addition to the identified terrestrial sites, the surrounding waters are likely to be critical
habitat for harbour seals, for feeding and/or for navigation to more offshore foraging areas.
Results from a study by the Coastal and Marine Research Centre (CMRC) on the haul-out
behaviour of harbour seals in southwest Ireland in recent years suggests that harbour seals
spend up to 80% of their time at sea (Cronin, 2007; Cronin et al., 2008). Similar behaviour
patterns have been seen in studies of harbour seals in Scotland (Sharples, SMRU pers
comm, Thompson & Miller, 1990). Unlike grey seals harbour seal adults continue to forage
during the breeding season (Bonnes et al., 1994). In addition the mating strategy is based
on males diving and calling at aquatic display sites (Van Parijs et al., 1997, 2000, Hayes et
al., 2004). Disturbance from anthropogenic noise during this period could potentially affect
mating success.
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The hearing range of harbour and grey seals extends over wide frequencies, including the
ultrasonic spectrum. The area of best hearing is between 8 and 25 kHz, with acute hearing
also at lower frequencies (Møhl 1968; Terhune & Turnbull 1995)
Considering the relatively large population of harbour seals using waters in Sligo Bay and
the proximity of haul-out sites to Sligo Harbour, there is high potential for harbour seal use of
the waters in the vicinity of Sligo Harbour and therefore they are the marine mammal species
most at risk to potential detrimental impacts of the proposed dredging and dumping.
Mitigation measures outlined in Section 6.4.8 will minimise potential impacts of the proposed
works.
Grey Seal
Grey seals are distributed throughout Irish coastal waters and commonly seen hauled out on
more exposed shores than the harbour seal (Kiely, 1998). Whilst there are no large colonies
of grey seals on the coastline of Co. Sligo, the bordering counties provide haul-out sites for a
significant proportion of the national population of grey seals. A national census of the grey
seal population in 2005 estimated between 795-1022 grey seals use breeding sites in Co.
Donegal and 1351-1737 use breeding sites in Co. Mayo (Ó Cadhla et al., 2007).
Grey seals use Inishmurray (54.433N 8.660W) and Rathlin O Birne Island (54.664N 8.827W)
as breeding sites (Ó Cadhla et al., 2005) and Ballysadare Bay and Ardboline (54.346N
8.693W) as moult sites (Ó Cadhla & Strong, 2007), where approximately 50 seals haul-out
to moult. Grey seals also use Inishmurray and Ballysadare Bay as haul-out sites outside of
the breeding and moult seasons; over 110 grey seals were recorded on Inishtrahull and 20
in Ballysadare Bay in August 2003 during the harbour seal census (Cronin et al., 2003).
Grey seals are also most vulnerable at their terrestrial haul-out sites during breeding and
moulting periods. These events occur between September and March in Ireland. There are
no known terrestrial sites for grey seals in the immediate proximity of the proposed works
however the surrounding waters are likely to be a critical habitat for grey seals, for feeding
and/or for navigation to more offshore foraging areas. Grey seals have a wider offshore
foraging distribution than harbour seals and as a result seals from large breeding colonies on
the coasts of Mayo and Donegal will be likely to use the waters of Donegal Bay and Sligo
Bay for foraging and/or navigation and therefore could potentially be affected by dredging
and dumping. Mitigation measures outlined in Section 6.4.8 will minimise potential impacts of
the proposed works.
6.4.3 Site visit
A visit to Sligo Harbour and adjacent coastal areas was made on March 18th and 19th 2011.
6.4.3.1 Methods:
The waters in the Sligo Bay and harbour were surveyed from a vantage point on the south
shore of the harbour using a telescope (equipped with a 30x eyepiece) mounted on a tripod
and 10 x 50 leica binoculars for all marine mammals at sea between 15:00 and 19:00 on
March 18th 2011 (2 hours either side of high tide) (Figure 6.47 to Figure 6.49).
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The shorelines of Sligo Bay and Drumcliff Bay were surveyed using 10 x 50 Leica binoculars
for all marine mammals ashore during the low water period between 09:20 and 13:20 (2
hours either side of low water) on March 19th. The low water period was surveyed in order to
maximise the likelihood of observing seals hauled out on rocks.
Observations of marine mammals at sea are affected by prevailing sea conditions with a
decline in sighting probability in Beaufort sea-states of three or higher. The conditions on
March 18th/19th were favourable for visual surveillance, with a Beaufort sea-state of one to
two and a light variable NE breeze.
6.4.3.2 Results:
One seal (unidentified species) was observed approximately 200m east of Oyster Island on
March 18th at 16:25.
One harbour seal was observed in the channel approximately 50m from the north shore near
Rosses Point on March 19th at 10:10.
No cetaceans were observed during visual observations, but given the limited time available
and the transient nature of cetacean movement patterns this does not indicate that the area
is not visited by dolphins or porpoises.
Drumcliff Bay
Rosses Point
Sligo Bay
Figure 6.47: Survey Area
(
denotes observation point for Sligo Bay marine mammal survey (source: ESRI topographical map)
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Figure 6.48:
Vantage point for marine mammal survey on south shore of Sligo
Harbour
Figure 6.49: North shore of Sligo Harbour at low tide, scanned for hauled-out
pinnipeds.
6.4.4 Potential Impacts of Dredging on Marine Mammals and Identification of
Sensitive Receptors.
The most likely impact of the proposed dredging activities in the harbour will be through
sound disturbance and local habitat modification. Benthic dredging activity can result in
significant modification to the biological environment. Destruction of benthic communities will
displace many species of invertebrate and fish and subsequently affect the food chain and
impact on marine predators. However, the effects of substrate removal will be determined by
the extent of dredging activity. In addition to the physical act of sediment removal, dredging
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activities will result in potential disturbance to marine mammals through increases in vessel
activity and increase local ambient marine noise levels.
Studies on the responses of marine mammals to anthropogenic noise have identified the
following factors as influencing the degree of response given by animals: (i) source intensity
levels, (ii) degree of background noise, (iii) distance to source, (iv) species involved, (v)
behavioural state and season, (vi) prior degree of exposure and (vii) age, sex and time of
day (Anguilar et al., 2004). The peak pressure, duration and the frequency spectrum of
anthropogenic sound are important factors relating to potential biological impacts. Several
studies have examined the direct and indirect impacts of underwater noise on marine
mammals and in general have indicated that source levels of 180-200dB P-P re 1 ȝPa are
sufficient to induce behavioural effects on marine mammals within a few kilometres of the
sound source (Gausland, 2000).
Biological damage from high-level sound may be categorized as either direct injuries (lethal,
sub-lethal or non-lethal) or indirect effects (changes in behavioural or distribution patterns).
Considering the proposed works in Sligo Harbour there is no potential for direct injuries to
marine mammals that could be caused by e.g. blasting. However there is potential impact
from underwater noise resulting from dredging. The physiological effect of exposure to
underwater noise can include temporary or permanent shifts in hearing thresholds, which
degrade an animal’s ability to forage and carry out other activities that depend on auditory
acuity such as communication, navigation and mating (Richardson et al., 1995).
There have been very few studies describing dredging noise from North America and the
UK, covering a variety of dredger types. The sparse data available indicate the predicted
vibration levels close to the source are relatively small and that dredging is not as noisy as
seismic surveys, pile driving and sonar; but it is louder than most shipping, operating
offshore wind turbines and drilling. Thompsen et al. (2009) suggest it should be viewed,
therefore, as a medium impact activity and because of its continuous source which might last
for extended periods, the potential adverse effects, especially in areas of high ecological
sensitivity should not be overlooked.
Noise associated with dredging is predominantly of low frequency, below 1 kHz; estimated
source sound pressure levels range between 168 and 186 dB re 1 ȝPa at 1 m. In most
cases the noise is continuous in nature. Audibility of dredging noise is dependent on many
factors (hearing sensibility of the species in question, prevalent ambient noise, transmission
loss etc). Since dredging noise is predominantly of low frequency, it would potentially affect
low frequency cetaceans such as minke whales to a greater extent than mid or high
frequency cetaceans. The harbour porpoise is a potential exception as it has a relatively
high sensitivity across most frequencies. There is also a potential issue with seals as both
harbour and grey seals have relatively good underwater hearing at frequencies below 1 kHz
(Thompsen et al., 2009)
Studies have shown that in shallow water, which would also characterise the situation at
most dredging sites, received sound pressure levels were above 140 dB re 1 ȝPa,
respectively at 1 km distance from the source; a value that is probably detectable for most
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marine mammals sensitive to sound pressure, depending on hearing abilities and local
ambient noise conditions. Even at 10 km distance, sound pressure levels were well above
120 dB re ȝPa, a value which might exceed ambient noise levels in several areas
(Thompsen et al., 2009).
The dumping of dredged material of fine sand and silt will likely affect water quality and
create a plume effect which will travel according to local water currents. This may have a
temporary impact on marine mammals’ visibility in the immediate vicinity of the vessel. The
changes to the benthos in this region caused by accumulation of dredged material on the
seabed will most likely invoke local changes in faunal assemblages and prey availability at
higher trophic levels, potentially affecting marine mammals.
To summarise, the potential effects of dredging and dumping on marine mammals include;
1. Physical injury or death of individuals resulting from collisions with operator vessels.
2. Chronic hearing damage or disturbance/displacement as a result of noise.
3. Consumption of contaminated prey items resulting from contaminants entering the
food chain (this is only a problem where contaminated substrates are disturbed).
4. Temporary impact on marine mammals’ visibility should they intersect the sediment
plume during the dumping of dredged material.
5. Changes in prey availability due to local changes in benthic ecology caused by
accumulation of dredge spoil on the seabed.
The likelihood and scale of each of these effects can be estimated and appropriate
precautionary mitigation measures should be employed to reduce the estimated effects.
6.4.5 Direct, Indirect and Cumulative Impacts of Proposed Dredging and Dumping of
Dredged Material on Pinnipeds.
The proposed dredging activities at Sligo Harbour are unlikely to cause detectable impacts
on seals at the population level. The numbers of seals in the adjacent coastal areas
represent a small fraction of local populations. There is a small possibility that impacts may
be suffered by individual grey or harbour seals entering the works zone. Sightings during
the field survey and local reports show that seals regularly enter the harbour area. However,
risks to these animals will be small and with a degree of vigilance from operators collisions
with seals and excessive disturbance will be avoided. Sediment plumes may present a
small level of habitat disturbance to local seals foraging in the area. Acoustic disturbance
can be a threat to marine mammals causing hearing damage however, noise levels from
vessels or from the dredging process are highly unlikely to cause hearing damage to
exposed seals provided they have the opportunity to leave the affected works area. As the
received sound pressure levels can be 140 dB re 1 ȝPa at 1 km distance from the source, a
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value that is detectable for seals, and as the area is of ecological importance2 (Figure 6.50) it
is suggested that appropriate mitigation measures be put in place to minimise acoustic
disturbance to seals (see Section 6.4.8).
The dumping of dredged material of fine sand and silt will have a minor impact on water
quality (discussed in more detail in Chapter 11). This may have a temporary impact on
marine mammals’ visibility in the immediate vicinity of the vessel. However this effect will be
temporary and as it is an open body of water 34 nautical miles from Sligo Harbour quayside
and in about 92m water depth, it is unlikely to cause any adverse effects on seals in the
area. The changes to the benthos in this region may temporarily affect prey availability to
seals in the area but as it is not a known ‘hotspot’ for seal foraging, displacement resulting
from impacts on available prey are unlikely. It is suggested that mitigation measures
outlined in Section 6.4.8 be followed to minimise any potential impact of dumping on
individual seals.
Figure 6.50: Proposed dredging area showing main environmental designations
2
Sligo Harbour holds a number of important environmental designations including the Cummeen Strand Special Area of
Conservation and the Cummeen Strand/Drumcliff Bay Special Protection Area. Nearby Drumcliff Bay is also a Special Area of
Conservation
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6.4.6 Direct, Indirect and Cumulative Impacts of Proposed Dredging and Dumping of
Dredged material on Cetaceans
The proposed construction activities at Sligo harbour are unlikely to cause detectable
impacts on cetaceans at the population level. There is little information indicating use of the
area by cetaceans and any exposure to sediment plumes or increased noise levels will be
temporary and non-threatening. The noise levels from vessels or from the extraction
process are unlikely to cause hearing damage to exposed cetaceans, provided they do not
approach the immediate vicinity of operations and have the opportunity to leave the affected
area. As the received sound pressure levels can be 140 dB re 1 ȝPa at 1 km distance from
the source, a value that is detectable for most cetaceans (in particular the auditory range of
harbour porpoise and minke whale, two of the most likely species of cetacean to visit the
area) and as the area is of ecological importance, it is suggested that appropriate mitigation
measures be put in place to minimise acoustic disturbance to cetaceans (see Section 6.4.8).
It is most likely that any effects of the proposed dredging work in Sligo harbour on cetaceans
will be minimal provided correct management and communication procedures are followed.
The dumping of the dredged material of fine sand and silt will likely affect water quality and
create a plume effect which will travel according to local water currents (these effects are
described in more detail in Chapter 11). This may have a temporary impact on marine
mammals’ visibility in the immediate vicinity of the vessel. However this effect will be
temporary and as it is an open body of water 34 nautical miles from Sligo Harbour quayside
and in about 92m water depth it is unlikely to cause any adverse effects on cetaceans in the
area. The changes to the benthos in this region will most likely temporarily affect prey
availability to cetaceans in the area, but as with seals the area is not considered (or known
to be) an important cetacean foraging area and therefore displacement resulting from
impacts on available prey are unlikely.
6.4.7 Assessment of impact magnitude and significance
It is considered that the proposed dredging at Sligo harbour and dumping of dredged
material west of Donegal Bay will have little likelihood of impacting on marine mammals in
the area at a population level. It is however recommended that vigilance should be
maintained for any marine mammal approaching the area throughout operations as there will
be potential effects of acoustic disturbance resulting from noise and boat activity associated
with dredging and dumping. The proposed dredging will occur during high tide, there is an
increased likelihood of marine mammals using the harbour at this tidal stage. As the
proposed works will take place within a Special Area of Conservation it is best practise to
employ a marine mammal observer to ensure impacts of coastal works (including dredging)
on marine mammals are minimised (D. Lyons, NPWS pers comm). The following
precautionary measures are therefore advised:
6-84
6.4.8 Marine Mammals - Mitigation Measures
A trained and experienced Marine Mammal Observer (MMO) should be put in place during
dredging and dumping operations. The MMO will scan the surrounding area to ensure no
marine mammals are in a pre-determined exclusion zone in the 30 minute period prior to
dredging operations. It is suggested that this exclusion zone is 500m, considering the
potential risks outlined.
x
Once operations have begun operations should cease temporarily if a cetacean or
seal is observed swimming in the immediate (<50m) area of industrial activity and
work can be resumed once the animal(s) have moved away.
x
Dumping of material at sea should not take place if a cetacean or seal is within 50m of
the vessel.
x
Any approach by marine mammals into the immediate (<50 m) works area should be
reported to the National Parks and Wildlife Service.
x
The MMO will keep a record of the monitoring using an MMO form “Location and Effort
(Coastal Works)” available from the National Parks & Wildlife Service (NPWS) and
submit to the NPWS on completion of the works.
x
If feasible, the MMO will take photographs of dorsal fins of Bottlenose dolphins
encountered, for the purpose of contributing to the Irish Whale and Dolphin Group
(IWDG) catalogue of images for photo-identification.
Many dredging contractors now have staff trained as MMOs within their dredging teams. If
the contractor does not have suitably trained staff, the cost for a marine mammal observer is
likely to be approximately €300-400 per diem (inclusive of employers PRSI & pension).
6.4.9 Marine Mammals - Residual Impacts
It is unlikely that there will be negative residual impacts of the proposed works on marine
mammals in the area. The changes to benthos in the dump area will most likely have short
long term impacts on prey availability to marine mammals in the area but as it is not known
to be a critical foraging area for marine mammals any effects will be negligible on both the
population as well as the individual level. The deepening of the navigation channel will likely
increase vessel activity in the area with an associated increase in underwater noise and
risks of collisions for marine mammals, but it is considered that the impacts of this will not be
significant on both the individual and population level for marine mammal species that
frequent the area.
6-85
6-86
Fisheries and Aquaculture
7.0
FISHERIES AND AQUACULTURE
7.1
INTRODUCTION
This Chapter describes fisheries interests in the area of the proposed dredging scheme in
Sligo Harbour and at the proposed dumpsite outside Donegal Bay, specifically with regard to:
x Commercial fisheries
x Shellfish aquaculture
x Salmonid migrations
x Eel & lamprey migrations
x Recreational sea angling
Also included is an assessment of impacts and recommended mitigation measures.
7.2
COMMERCIAL FISHERIES
Fisheries are considered in the areas of both the proposed dredging activity and the
proposed dumpsite for dredged spoil materials.
Dredging Area
The course of the navigation channel into Sligo port and the area proposed for dredging is
shown in Figure 4.1 in Chapter 4, “Project Description”. There is little fishing activity in the
proximity of area to be dredged within Sligo Harbour apart from some limited potting for
lobster along the shore to the north of the channel. Outside of Sligo Harbour there is further
potting for lobster and crab together with a limited degree of gill netting.
Proposed Dumpsite
The material from the proposed dredging of the channel in Sligo Harbour is to be dumped at
a proposed offshore location outside Donegal Bay (see Figure 4.2 in Chapter 4, “Project
Description”). The dumping site is located in ICES statistical rectangle 38E0 and is
approximately 17km from Malin More Head and 30km north of the nearest point on the north
Mayo coast. This site is in an important area for Brown crab fishing, although the most
intensive fishing activity is probably to the west of the actual dumping area.
7.2.1 Irish Brown Crab Fishery
The Irish fishery for Brown crab (Cancer pagurus) has been examined in detail by Tully et al
(2006) in a BIM report produced for the national Crab Management Advisory Group, a
committee of the Management Framework for Shellfisheries which advises the Department of
Agriculture, Food and the Marine (DAFM) on the management of shellfisheries. This
assessment is based largely on the findings of the BIM report and supplemented with
updated information through consultation with local BIM representatives covering the north
Mayo, Sligo and Donegal region.
Landings of brown crab into Ireland in the last decade reached a peak of over 14,200 tonnes
in 2004 with a value of almost €17 million, falling to 8,600 tonnes worth €12.85 million in
2010 (Table 7.1). In terms of value, from 2001 to 2005 brown crab was in the top five most
7-1
important species of fish landed into Ireland; catches have since declined but remain in the
top ten species landed.
Table 7.1: Total landings of brown crab into Irish ports, 2001-10 (Source: SFPA)
Year
Live wt (tonnes)
Value (€000s)
2001
10,312
13,109
2002
10,098
13,213
2003
10,655
10,231
2004
14,217
16,992
2005
9,527
9,571
2006
10,827
8,223
2007
9,251
na
2008
7,640
9,149
2009
6,614
na
2010
8,621
12,847
Landings increased by approximately 500 tonnes per year between 1990 and 2004 with a
higher rate of increase during the latter half of this period (Figure 7.1). The Irish fleet can be
divided into <12m vessels which land crab on a daily basis and a more mobile >18m vivier
fleet which can carry live crab onboard and remain at sea for extended periods. The vivier
fleet fishes off the northwest coast although, through modernisation, the <12m fleet has
increased its seaward range and can fish outside the 12nm limit on a daily basis.
14000
National crab landings
1952-2004
Tonnes of crab landed
12000
10000
8000
6000
4000
2000
2004
2000
1996
1992
1988
1984
1980
1976
1972
1968
1964
1960
1956
1952
0
Figure 7.1: National landings of brown crab between 1952 and 2004 (from Tully et al,
2006; reproduced by permission of BIM)
7-2
7.2.1.1 Biology of the Brown Crab
The brown crab or edible crab (Plate 7.1) is a decapod crustacean and is the largest of the
common crabs found in Irish waters. It is widely distributed in Irish and British waters, and
throughout north-western Europe. Brown crab can live for at least 15 years - mating first
takes place is in spring and summer when the females are 5-6 years old and occurs shortly
after the female has moulted. Females are 'berried', carrying the eggs under the abdomen
over winter for 6-9 months and releasing the larvae in late spring/early summer. Crabs have
a high fecundity with each female hatching 1-4 million eggs depending on size. Post-larvae
settle in inshore areas and juveniles are often found in shallow waters. Adult crabs are
migratory and undertake extensive seasonal migrations, probably associated with the
reproductive cycle.
Plate 7.1: Brown Crab
Tully et al (2206) consider that Irish stocks are probably regional in scale (>100km) with a
variable range from the coast to offshore waters. The authors also note that crabs on the
northwest coast may be regarded as a single functional unit distributed over a wide range off
the northwest coast of Ireland and west of Scotland (Figure 7.2).
7.2.2 The North West Crab Fishery
A significant proportion of the national crab catch is taken in the northwest fishery and is
landed into Donegal and Mayo (Figure 7.3).
7.2.2.1 Fishing activity in the north Mayo area
The crab grounds off the north Mayo coast form a significant part of the North West crab
fishery which is the largest stock fished by Irish vessels. The area is fished predominantly by
vessels of <12m from ports on the north Mayo coast but also including ports on the Sligo
coast and extending round into south Donegal. These vessels may steam five to six hours
offshore to the fishing grounds.
Many of the fishermen in the north Mayo area are represented by the Erris Inshore
Fishermen’s’ Association (EIFA) which covers ports from Belderrig to Doohoma – the group
has around 50 members. All vessels concentrate on shellfish although not all fish in the area
under consideration. A second group, the Erris Lobster Conservation and Restocking
Association operates more locally in the Erris area.
7-3
Figure 7.2:Probable distribution of the northwest crab stock (from Tully et al, 2006;
reproduced by permission of BIM)
9000
Crab landed into
Donegal and Mayo
8000
Tonnes of crab
7000
6000
5000
4000
3000
2000
1000
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
0
Figure 7.3: Annual landings of crab into Donegal and Mayo, 1990-2004 (from Tully et
al, 2006; reproduced by permission of BIM)
7-4
The crab fishing area overlaps with the pelagic fishery operating out of Killybegs and there is
an agreement in place between EIFA and the Killybegs Fishermen’s Organisation (KFO) to
avoid damage to static gear from trawling activities.
In 2004 over 1,500 tonnes of crab was taken by the Mayo <12m fleet in ICES rectangle
38E0, in which the proposed dumpsite is located (Figure 7.4). However, it is believed that
more vessels are now active in this area and the annual crab catch is now in excess of 2,000
tonnes (D Nee, BIM; pers comm).
Figure 7.4: Landings of crab by statistical rectangle by the Mayo and Donegal <12m
fleets in 2004 (from Tully et al, 2006; reproduced by permission of BIM)
Peak fishing activity takes place from spring to early autumn during the months May to
September, with activity declining between October and December, and fewer vessels
operating from February to April. However, 6-8 boats now fish year round and the fishery is
developing towards a 12-month operation.
Landings per unit effort (LPUE) data for the offshore fishery has been examined by Tully et
al, (2006) while LPUE data for <12m vessels from the inshore fleet at Malin Head, Co.
Donegal has been compiled by Meredith & Fahy (2005). A significant decline in LPUE has
been observed in both sectors although the latter dataset suggests an increase in LPUE in
the inshore fishery.
7-5
7.2.2.2 Size composition
Tully et al (2006) have presented data on the size composition of landings from the inshore
fishery (Figure 7.5).
1200
Female crab 1996,
n=6685
Number of crab
1000
800
600
400
200
220
210
200
190
180
170
160
150
140
130
0
900
800
700
600
500
400
300
200
100
0
220
210
200
190
180
170
160
150
140
Female crabs
1997,n=5788
130
Number of crab
Carapace length (mm)
45
40
35
30
25
20
15
10
5
0
220
210
200
190
180
170
160
150
140
Male crabs
1996,n=232
130
Number of crab
Number of crab
120
Male crabs
1997,n=651
100
80
60
40
20
220
210
200
190
180
170
160
150
140
130
0
Carapace length (m m)
Figure 7.5: Size composition of male and female crab in the inshore landings 1996/97
(from Tully et al, 2006; reproduced by permission of BIM)
The current legal minimum landing size (MLS) of 130mm carapace width is of little
significance as there is a market-driven “limit” of 140mm and the modal landing size is 155165mm. The size composition of crabs in both offshore and inshore fisheries remained
7-6
constant between 1997-2001, during a period of increased fishing effort and increased
landings.
Mean size at maturity is approximately 120mm carapace width and all crabs appear to be
mature at about 140mm.
7.2.2.3 Changes in fishing area and effort between 1997 and 2005
Tully et al (2006) describe a shift in fishing activity between 1997 and 2005 with an increased
effort in the north Mayo area. In 1997 effort by vessels <12m was concentrated to the north
of Malin Head and to the west of Donegal (Figure 7.6). However, by 2005 the main area of
fishing activity by these vessels had shifted to northwest Mayo and north Donegal (Figure
7.7).
Further data presented by Tully et al (2006) illustrates that the number of vessels in the
northwest fishery declined significantly between 1997 and 2005 but that fishing effort in terms
of the number of pots fished had increased significantly during the same period.
In 1997 there was an estimated 129 Donegal based boats fishing crab with a further 24
fishing out of north Mayo ports. By 2005 the combined number of vessels targeting the
fishery from both north Mayo and Donegal had fallen to 60 including the large vivier boats
fishing further offshore. There has therefore been a decline in the region of 50% in the
number of vessels targeting crab during this period.
However, during this time the number of pots and the potential fishing effort has increased
markedly. Data from a sample of vessels <12m in length, suggested that a total of 26,000
pots in the inshore fleet had increased by 60% to almost 42,000 by 2005. Therefore,
although there was a reduction in the number of vessels in the fishery, an increase in the
number of pots per vessel had resulted in an overall increase in effort.
It is understood that he density of gear deployed in the north Mayo area has increased
further since 2005 (D Nee, BIM; pers comm).
7.2.3 Other Inshore Fisheries
Additional fishery activity in the inshore area incorporating the proposed dumpsite includes
trawling and gill-netting. The main trawling activity is associated with the pelagic fishery for
mackerel, horse mackerel and herring and usually takes place between September and
December.
Gill-netting for other species (e.g. turbot, rays) is a much smaller fishery. The scope of gillnetting is limited by a restriction which prohibits their deployment to the north of 54o 30’,
which lies approximately 5km to the south of the proposed dumpsite.
7-7
Figure 7.6:Distribution of fishing in the <12m and vivier crab fisheries in 1997 (from
Tully et al, 2006; reproduced by permission of BIM)
x
Each rectangle, colour coded by Malin, Northwest Donegal and west Donegal is the
approximate extent of fishing by one vessel. Mayo fishing effort is not included but was
mainly distributed along the north and northwest of Mayo in 1997.
7-8
Figure 7.7: Distribution of fishing in the <12m and vivier crab fisheries in 2004-2005
(from Tully et al, 2006; reproduced by permission of BIM)
x
Each rectangle, colour coded by Malin, Northwest Donegal and north Mayo is the
approximate extent of fishing by one vessel
7-9
7.3
AQUACULTURE
7.3.1 Introduction
There are three areas of shellfish production in the Sligo area – Drumcliff Bay, Sligo Harbour
and Ballysadare Bay. The local industry is based on the production of bivalve molluscs and is
the main area in Ireland for production of Manila clam (Tapes philippinarum or T
semidecussatus); other species produced in the area are Pacific oyster (Crassostrea gigas),
and Blue mussel (Mytilus edulis) (Plates 2-4). The location of areas licensed for shellfish
production in the three bays and designated species are shown in Figure 7.8.
Plate 7.2: Manila clam
Plate 7.3: Blue mussel
7-10
Plate 7.4: Pacific oyster
Figure 7.8: Sites licensed for shellfish production in the Sligo area
7.3.2 Shellfish Production
7.3.2.1 Manila clam
Manila clam is a non-native species and was introduced into Ireland in 1982 by the UCG
Shellfish Research Laboratory at Carna. It is very similar to the native species, but with
superior growth and survival rates. The Manila clam is also tolerant of a wide range of
salinities but requires more wave-sheltered conditions for on-growing than mussel or oyster.
The introduced clam was found to be easy to produce in hatchery conditions, resistant to
disease and had a high survival rate. Adult clams are conditioned in the hatchery during the
7-11
winter and then induced to spawn. The resultant larvae develop into spat or seed, the first
recognisable adult stage. Seed from the hatchery is placed initially in off-bottom frames until
they are ready for planting into on-growing areas known as “parcs”. Half-grown clams are
planted out in shore plots where they bury in the substrate. Netting is used to retain the stock
within a confined area and to protect against predators - crabs and birds, notably
oystercatcher, can cause serious losses if growing areas are not adequately protected. The
clams feed on phytoplankton and filter their food from the water through a siphon that is
pushed up through the sediment. Harvesting takes place after a growth cycle of
approximately 3 years and the stock is then purified and graded in preparation for the French
market.
Shellfish production is now concentrated on production of Manila clam which was first
cultivated in Drumcliff Bay in the early 1980s. There are now two main companies operating
in Drumcliff Bay (Armada Shellfish Co Ltd & Atlantic Clams Ireland Ltd), and a single leading
company in Sligo Harbour (Coney Island Shellfish Ltd). Four on-growing companies in Sligo
Harbour work collectively through Coney Island Shellfish with licensed areas in the
Cummeen Strand area. Growers are supplied with juvenile clam by a locally based hatchery,
Lissadell Shellfish Co Ltd, which has also been in production since the 1980s and is the
largest producer of clam seed in Ireland.
7.3.2.2 Oyster
Pacific oyster is also a non-native species which do not spawn naturally in local waters. The
industry therefore depends on specialist hatchery producers, such as Lissadell Shellfish, for
the supply of seed for on-growing in coastal areas. Pacific oysters are usually grown in
plastic mesh bags secured to metal trestles in the inter-tidal zone or low-water mark.
Alternatively, juveniles may be laid directly on to the seabed plots or ‘parcs’ on the inter-tidal
area. The oysters feed on natural phytoplankton and reach market size of 70-100g in 2-3
years.
There are licensed areas for oyster cultivation in both Drumcliff Bay and Sligo Harbour.
There has been little production in recent years but Coney Island Shellfish has taken in some
stock this year in 2012.
7.3.2.3 Mussel
Mussel farming is based on the bottom culture of mussels laid as seed (or spat) for growing
on to harvest size. The spat is dredged from known areas around the Irish coast where it has
settled in abundance - this takes place between July and November. The seed is then
transferred to prepared areas where it is re-laid at lower density to promote improved growth
and meat content. Harvesting of mussels is generally between November and March but can
occur throughout the year.
Mussel cultivation is very much constrained by the availability of seed mussel which has
been unable to fully meet the demands of the industry through a period of rapid expansion.
Most of the seed mussel for the industry is dredged from the south west Irish Sea, and a
Seed Mussel Allocation Committee (SMAC) comprising representatives from BIM, DCENR,
7-12
DARD, CBAIT and the Loughs Agency considers the supply and allocation of seed
throughout Ireland.
Areas of Ballysodare Bay are licensed for mussel cultivation but there does not appear to
have been any production in recent years.
7.3.3 Annual Production
Shellfish have been cultivated in the Sligo Bay area since the 1980s with designated licensed
areas in Drumcliff Bay, Sligo Harbour and Ballysadare Bay. Production is focussed on Manila
clam and this is the main area of clam production in Ireland. Smaller quantities of Pacific
oyster are also produced and areas of Ballysadare Bay are licensed for bottom grown
mussel, but there appears to have been no activity with this species in recent years. Clam
production is also mainly from Sligo Harbour and Drumcliff Bay.
Annual production figures for 2006 to 2011 indicate that total annual shellfish production from
the area in recent years has ranged from 183 to 285 tonnes with a value of up to €1½ million.
Table 7.2: Clam and oyster production in the Sligo Bay area, 2006-11 (Source: BIM)
Year
7.4
Clam
Oyster
Combined
Volume (t)
Value (€)
Volume (t)
Value (€)
Volume (t)
Value (€)
2006
244
1,374,180
34
74,800
278
1,448,980
2007
158
934,000
25
40,000
183
974,000
2008
171
922,000
114
373,000
285
1,295,000
2009
122
845,000
72
113,800
194
958,800
2010
130
825,000
68
148,400
198
973,400
2011
125
730,000
67
146,800
192
876,800
Shellfish Waters Directive
The EC Shellfish Waters Directive (2006/113/EC) requires member states to designate
waters that need protection in order to support shellfish life and growth. The Directive is
implemented in Ireland by the European Communities (Quality of Shellfish Waters)
Regulations 2006 (SI No 268 of 2006). It is designed to protect the aquatic habitat of bivalve
and gastropod molluscs, and sets physical, chemical and microbiological requirements which
designated waters must either comply with or endeavour to improve. Sligo Harbour and
Drumcliff Bay have been designated as shellfish waters while Ballysadare Estuary/Bay has
not been designated.
Article 5 of the Directive provides for the establishment of Pollution Reduction Programmes
(PRPs) for designated waters. PRPs for the designated shellfish waters in County Sligo were
made by the Minister of DoEHLG in December 2009.
The directive will be repealed in 2013 by the EC Water Framework Directive, which will
provide at least the same level of protection to shellfish waters
7-13
7.4.1 Classification of Shellfish Production Waters
Shellfish production areas are classified by the Sea Fisheries Protection Authority (SFPA)
based on monthly monitoring of shellfish for bacterial contamination in accordance with the
terms of EU Regulations 853 and 854 (2004). Each harvest area is assigned Class A, B or C
according to their sanitary quality using E coli as an indicator of sewage contamination.
Shellfish from Class A areas may be marketed for direct human consumption, while product
from Class B or C areas must be relayed or subjected to purification/heat treatment prior to
marketing. The most recent classifications with regard to local production sites are shown in
Table 7.3. Drumcliff Bay and Ballysodare Bay have previously held Class A designation for
oyster and mussel respectively.
Table 7.3: Classification of designated bivalve mollusc production areas, 2012
Production
Area
Drumcliff Bay
Sligo Harbour
Ballysodare Bay
Boundaries
Bed
Name
Raghly Point to
All beds
Deadman’s Point
Deadman’s Point
All beds
to Killaspug Point
Killaspug Point to
Derkmore Point
All beds
Species
Current
Classification
Oyster
B
Clam
B
Mussel
B
Cockle
B
Oyster
B
Clam
B
Mussel
B
Despite these controls, outbreaks of viral illness associated with shellfish consumption can
occur. One of the principal agents related to such outbreaks is Norovirus (NoV) which causes
gastroenteritis. Norovirus was detected in shellfish originating from Drumcliff Bay in 2010 but
this has since been eradicated.
7.4.1.1 Brown Ring Disease
Brown Ring Disease (BRD) is caused by Vibrio tapetis, a gram-negative, motile bacterium
which can infect wild and cultivated clam species. BRD was detected in clams beds in
Brittany in 1987 and has spread along the European Atlantic coast. It has recently been
detected in stock from both Drumcliff Bay and Sligo Harbour but has not led to any major
problems with the stock.
7.4.1.2 Biotoxin and Phytoplankton Monitoring
Samples of shellfish are routinely collected from aquaculture production sites as part of the
National Biotoxin Monitoring Programme. These samples are analysed for the presence of
toxins belonging to the Amnesic Shellfish Poison (ASP), Diarrhetic Shellfish Poison (DSP),
Paralytic Shellfish Poison (PSP) and Azaspiracid Shellfish Poison (AZP) toxin groups. Water
samples from shellfish production sites are also collected for determination of the level of
known toxin producing phytoplankton species and harmful/nuisance phytoplankton species.
7-14
7.5
SALMONID MIGRATIONS
7.5.1 Life Cycle
Atlantic salmon Salmo salar and sea trout Salmo trutta (Plates 6 and 7) both have marine
and freshwater phases of the life cycle. Adult fish spawn in freshwater rivers where their
young develop for 1-3 years before migrating to richer feeding grounds at sea. The maturing
adult fish return to freshwater to breed after 1-2 years at sea. Migrations to and from local
rivers will require these fish to pass through the dredging area in Sligo Harbour.
Plate 7.5
Atlantic salmon
Plate 7.6
Sea trout
7.5.2 Salmon Conservation
The Atlantic salmon is listed in Annex II of the EU Habitats Directive (92/43/EEC) as a
species of European importance. EU member states are required to designate and manage
sites for listed species or habitats as a part of wider measures to ensure the conservation of
the habitats and species.
For several years fisheries scientists have been concerned about the declining numbers of
salmon returning to the Irish Coast due to a persistent phase of low marine survival. Since
7-15
1996 a progressive series of conservation initiatives have been introduced to address this
decline in stocks culminating in the closure of mixed stock coastal fisheries in 2007. Salmon
stocks in Ireland are now managed on an individual river basis with the objective that each
river must exceed its Conservation Limit for there to be any exploitation of fish to be
permitted either by nets or rods.
The Scientific Sub-Committee of the National Salmon Commission provides annual advice
on harvest options for individual rivers in order to ensure that there are sufficient spawning
salmon remaining in each system to meet the required conservation limit. The leading
salmon rivers in the Sligo fisheries district are currently open for salmon angling, although the
Garravogue is subject to specific restrictions due to a restricted quota.
7.5.3 Local salmon/sea trout rivers
There are a number of rivers discharging to Sligo Bay via Drumcliff Bay, Sligo Harbour and
Ballysodare Bay, all of which support one or both of the migratory salmonids species, Atlantic
salmon Salmo salar and sea trout Salmo trutta. The principal rivers in this regard are the
Ballysodare, the Garravogue and the Drumcliff (Figure 7.9). Annual salmon catches in each
of these river systems is shown in Figure 7.10. There is currently no commercial netting for
salmon in the estuaries of these rivers.
Figure 7.9: Map of region showing principal salmonid rivers draining to Sligo Bay
7-16
Figure 7.10: Annual salmon catch from principal local rivers, 2001-10 (Source: IFI)
7.5.3.1 Ballysodare River
This is one of the leading and most productive salmon rivers in Ireland. Due to extensive
conservation measures by the Ballysodare Fishing Club and IFI in recent years, there is now
a substantial run of spring salmon in the river from April to mid June. This is followed by a
large grilse run which peaks in June – July. There is some substantial run of sea trout into
the estuary on rising tides.
7.5.3.2 Garravogue River, Lough Gill and Bonet River system
The Garavogue is only just over 4 km in length from Lough Gill to the tidal reach. It is
predominantly fished on the east side of Sligo town close to where it flows out of. The river
gets a run of spring fish early in the year and later a larger run of grilse. There are a series of
angling clubs and privately owned fisheries throughout the system.
7.5.3.3 Drumcliff River and Glencar Lake
This system has a good stock of sea trout and also a modest run of salmon, both early spring
fish and summer grilse.
7.5.4 RECREATIONAL SEA ANGLING
7.5.5 Shore Angling
There are strong currents in the navigation channel in Sligo Harbour but there good fishing is
available in the channel from the north side between Rosses Point and Deadman’s Point for
sea trout, mackerel, bass, dogfish, bull huss, ray and tope. The channel can also be
accessed from the south side via Coney Island. The beach on the west side of Coney Island
is also noted for bass, flounder and occasional ray.
7-17
7.5.6 Boat Angling
Two charter boats based in Rosses Point and operate specifically in Sligo Bay and provide
reef fishing and general inshore angling for tope, ray, spurdog, dogfish and occasional large
skate. A number of boats based in Mullaghmore offer fishing in the wider Donegal Bay area.
The Turbot Bank to the north west of the mouth of Ballysadare Bay is a recognised area for
turbot, thornback ray and blonde ray. Another reef is ‘the Ledge’ which lies about 6.44km
west of Coney Island with excellent pollack fishing. Ling, conger, tope and bull huss may also
been taken in the vicinity while the area south of ‘Wheat Rock’ produces common skate to
more than 150lbs (68kg).
Sligo Bay also provides good fishing opportunities locally for small boat angling and as this
niche of saltwater angling increases in popularity so the fishing on Sligo Bay will be opened
up to a wider public.
7.6
EEL & LAMPREY MIGRATIONS
7.6.1 Eel (Anguilla anguilla)
Eels have a catadromous life cycle - young eels (elvers) migrate from the sea into freshwater
to feed and the resultant adults later return to sea to spawn. Juvenile eels are likely to be
present in the local estuaries in the Sligo area during March and April. They are then
believed to spend 10-15 years in freshwater systems before beginning their return migration
to sea during the autumn period as silver eels. Silvers are therefore likely to be moving out
through local estuaries during late autumn and early winter.
Eels have been fished commercially in the Ballysadare and Garravogue systems. However a
long term and widespread decline in European eel stocks has been a matter of concern for
some time leading to EC European Eel Regulation (EC) No 1100/2007 in 2007. This
Regulation aims to establish measures for the recovery of the European eel stock in the form
of Eel Management Plans for each eel river basin including Western River Basin District
which includes all catchments draining to Sligo Bay. This will require Member States to
reduce exploitation on all major eel river basins and must demonstrate that at least 40% of
the biomass of adult eels are escaping to sea to spawn.
7.6.2 Lamprey
There are two migratory species of lamprey with marine phase in their life cycle, Sea lamprey
(Petromyzon marinus) and River lamprey (Lampetra fluviatilis) – both are listed in Annexe 2
of the EC Habitat Directive. Adult sea lamprey enter the estuaries of rivers from April
onwards, and migrate some distance upstream to spawn which usually takes place in late
May or June.
The juvenile larval phase is variable but averages about five years with subsequent
metamorphosis to the adult form takes between July and September. The timing of the main
migration downstream also varies and relatively little is known about the adults after they
7-18
reach the sea, where they have been found in both shallow coastal and deep offshore
waters.
The life cycle of the River lamprey is very similar to that of the sea lamprey. Mature adults,
having spent one to two years mainly in estuaries, stop feeding in the autumn and move
upstream into medium to large rivers, usually migrating into fresh water from October to
December.
Spawning takes place during March and April. The juveniles live and feed within silty river
substrates for up to 5 or 6 years before metamorphosing into fully formed adults and then
migrating downstream to estuaries or the open sea for the adult feeding cycle.
The presence of eel and lamprey including (migratory phases) in local estuaries is
summarised in Table 7.4.
Month
Eel
Sea lamprey
River Lamprey
Jan
Adults present in estuary
Feb
Mar
Elvers moving in
through estuary
Apr
Elvers moving in
through estuary
May
Adults moving
upstream
Adults moving
upstream
Jun
Jul
Silvers moving out
through estuary
Young moving
downstream
Aug
Silvers moving out
through estuary
Young moving
downstream
Sep
Silvers moving out
through estuary
Young moving
downstream
Oct
Adults present in estuary /
Adults moving upstream
Nov
Dec
Table 7.4: Summary of migrations/presence of eel and lamprey in local estuaries at
different times of year
7-19
7.7
IMPACT ASSESSMENT
7.7.1 Potential Effects of Dredging and Disposal of Dredged Materials at Sea
7.7.1.1 Dredging
The potential environmental impacts of marine dredging are summarised by MEMG (2003): a
major effect will be the re-suspension of the bottom sediments and its effects on water
turbidity and the liberation of any materials contained and sequestered within the sediments.
The release of these materials into the water column will then have the potential for a
biological effect. In turn, these effects have the potential to influence the fisheries and nature
conservation value of the area. Specifically, in this assessment the impacts on shellfish
aquaculture and salmonid migrations are considered.
The wider environmental effects of dredging have been summarised in a conceptual model
(Figure 7.11). The pathway for potential impacts on shellfish aquaculture and salmonid
migrations can be traced in this model.
7.7.1.2 Disposal of Dredged Materials at Sea
The potential environmental impacts of disposal of dredged material are also summarised by
MEMG (2003): the disposal of dredged material will have the potential to affect the water
column, the bed conditions and their biota. Dumping of sediments will lead to increased
turbidity in the immediate area and in the area of sediment plume dispersal. The release of
any materials contained within the dredged material, may be the result of the changed
chemical environment. Similarly, any organic matter in the sediment will create a water
column oxygen demand. The deposited sediment will also change the nature of the bed
sediment, if it is of a different particle size and it can have a smothering effect on the bed
community as well as bringing new organisms to an area. Both of these features will affect
the structure of the bed community and in turn the demersal and benthic fishes feeding on
that bed community. This assessment is concerned primarily with near and far-field impacts
on commercial fishing activities in the area of the proposed dredge disposal site.
The wider environmental effects of dredging have also been summarised in the conceptual
model (Figure 7.12). The pathway for potential impacts on the commercial fishery can be
traced in this model.
7.7.2 Socio-Economic and Conservation Aspects
Whereas most of the above impacts of dredging and disposal of dredged materials relate to
the ecological system, the resultant impacts on the uses and users of the marine
environment are often of greater prominence and more public concern. These include the
actual or perceived effects on socio-economic aspects such as fisheries, and aesthetic
aspects including recreation and tourism.
Similarly, the perceived or actual effects on the conservation importance of an area will be of
concern, especially where the habitats and species within and adjacent to the dredging and
disposal areas are of importance (MEMG, 2003).
7-20
Figure 7.11: The potential environmental impacts of marine dredging - a conceptual
model
(reproduced from MEMG, 2003)
Figure 7.12: The potential environmental impacts of marine dredged material disposal
- a conceptual model
(reproduced from MEMG, 2003)
7-21
7.7.3 Impact Hypotheses
7.7.3.1 Dredging Area
area during the dredging operations. The modelling was used to examine the effect of the
dispersion and fate of material spilled during the period of the dredging operations.
Tidal flow modelling indicated that:
x
while the proposed dredging will lower the level of the low water spring tides in the
channel at Sligo, the high spring tide level will be unaffected by the proposed dredging
works.
x
dredging will have an insignificant effect on the current flows in the harbour area except
in the area of the channel and adjoining northern section of the harbour.
Dredging plume simulation modelling indicated that:
x
sediment is temporarily deposited along the sides of the channel and along the north
shore of the harbour area during both the water injection and conventional dredging
operations.
x
The peak deposition envelope values of 20-70mm will be of a short duration and tend to
occur during the turn of the tide. Following the water injection dredging much of the
displaced material will ultimately settle in the vicinity of the Bungar Bank (to depths of
less than 3mm) and the remainder will settle around the training walls and Cummeen
Strand, again to depths of less than 3mm (refer to Figure 11.8 in Chapter 11. Following
completion of conventional dredging operations, residual deposits of sediment will be
confined again to the areas around the training wall and the northern shore of Sligo
Harbour (refer to Figure 11.26).
x
Away from these areas the amount of deposition from sediments settling out is small.
x
Sediment disturbed by dredging in the upper navigation channel will cause temporary
increases in suspended sediment concentration in the lower 0.5m of water column at
licensed aquaculture sites, but overall concentrations will remain relatively low.
x
During the conventional dredging operations, mean suspended sediment concentrations
in the lower 0.5m of water column in the navigation channel will be within the
recommended limits for salmonid waters as prescribed by the EC Freshwater Fish
Directive. During the water injection dredging operations, mean suspended sediment
concentrations in the lower 0.5m of water column in the navigation channel will be
slightly above recommended levels, however the duration of these increases will be
temporary, lasting only a few days.
7.7.3.2 Disposal Site Dispersion
The impact of the dumping operation on sedimentation and suspended sediment loads in the
area of the proposed dumping site outside Donegal Bay was assessed by undertaking a
computational modelling exercise. Drogue measurements were also carried out to provide
information on tidal currents in the surface, middle water column and bed layer during neap
and spring tides – this data was used in calibration of the model.
7-22
The key findings of this exercise are:
x
tidal velocities in the area the dump site are small with peak spring tidal velocities of
circa 0.16 m/s.
x
the majority of the material will be deposited and remain within 2km of the dumping site
with only a small amount of material being transported further offshore by the residual
current.
x
finer materials will be more easily re-suspended and will be gradually transported
towards the open sea due to the residual current.
x
suspended sediment values beyond the immediate vicinity of the dumping operation will
be minimal and the material will not be transported a significant distance before current
speeds reduce at slack water and the material is deposited.
x
sediment transport due to wave action is likely to be limited due to the water depth of
90m.
x
tidal currents in the area of the dump site are weak and any material driven into
suspension during large swell events will not be transported far from the site due to the
weak tidal currents.
7.7.4 Potential Impacts of the Scheme
7.7.4.1 Dredging Area
Shellfish Aquaculture
There will be no effects on aquaculture operations in either Drumcliff or Ballysadare Bays as
the respective licensed areas in each bay are sufficiently isolated from any elevations in
suspended sediment or deposition of sediments due to dredging activities in Sligo Harbour.
Sediment deposition at licensed aquaculture sites in Sligo Harbour during the water injection
dredging is predicted to be very low (<2mm) for the short duration of these operations.
During the conventional dredging operations sedimentation is also predicted to be very low
(<2 mm) during dredging of both the upper and lower channel, while on completion of the
works will be lower still (0-1 mm). Manila clam under cultivation at these sites are buried
naturally in the substrate and will be unaffected by these negligible levels of sediment
deposition. Sediment deposition at the aquaculture sites during and following water injection
maintenance dredging operations will also be barely perceptible (0-1mm).
It can be seen that when dredging operations occur during spring tides, the suspended
sediment concentration at each of the four sites shown in Figures 11.11 - 11.15 and 11.36 11.39 in Chapter 11 rises quickly (around the period of slack water during each tide) but it
also quickly returns back to the background values.
During spring tides, the suspended sediment concentrations reach relatively high peak
values during each tide (when compared to the measured background in Table 11.4 in
Chapter 11), however the actual duration of each “spike” is very short (as dredging only
occurs for a short period each tide).
7-23
During dredging operations the concentration peaks, or “spikes” at any given point will
typically last two to three hours, but with the highest values lasting for a period of only 15-30
minutes. The period between peaks (tides), when concentrations return back to baseline, or
near baseline levels, will be much longer (around 9-10 hours). Cultivated shellfish buried in
the substrate at these sites will be unaffected by these short term elevations in suspended
sediment.
Based on these projections there will be no impacts on shellfish aquaculture in Sligo
Harbour.
Salmonid Migrations
Fish migrating through estuarine environments may frequently encounter high suspended
sediment loads which do not appear to impede this behavioural activity. Atlantic salmon are
known to move through the Severn Estuary where sediment concentrations in suspension
can reach into several thousand mg/l for periods (Gibson, 1933). Simenstad (1988) suggests
that salmonids are likely to have adapted physiologically to the turbid conditions that occur
naturally within estuarine and harbour areas.
It has also been shown that while the concentration of suspended sediment in the water
column is important, the duration of exposure is also a key factor (Newcombe & MacDonald
(1991). Salmon and other fish species will exhibit avoidance reactions to locally adverse
water quality and move away from the immediate vicinity of conditions. Simenstad and
Nightingale (2001) have recommended a turbidity threshold of 200 mg/l in dredging areas to
avoid the higher levels of suspended materials that are known to cause physical injury.
Suspended sediment concentrations in the lower 0.5m of water column are predicted to
remain relatively low throughout conventional dredging operations, however there will be
significant suspended sediment levels of short duration occurring in the navigation channel
during each tide for 2-3 days on the period of spring tides during and following the water
injection dredging operations.
Adult salmonids are most likely to move upstream via the navigation channel where the
mean concentration will be slightly higher (60mg/l) than the Fish Directive recommended limit
of 25 mg/l for salmonid waters for a period of a few days during the water injection dredging.
During the longer period of conventional dredging the mean suspended sediment
concentrations throughout this time will be slightly higher than background, but will remain
within the Fish Directive recommended limit of 25 mg/l for salmonid waters. Moreover, for all
dredging activities suspended sediment concentrations are likely to be lower closer to the
surface of the water column, which salmon more commonly utilise when swimming through
estuarine and coastal waters.
Similarly, downstream migrant salmon and sea trout smolts will have no difficulty in dealing
with the projected conditions in this respect.
Projected levels of suspended sediment are within recommended guidelines and will
not have an adverse effect the upstream and downstream migration of salmonids.
7-24
Eel & lamprey
On migrating through estuarine environments these species may frequently encounter high
suspended sediment loads which do not appear to impact on migrations.
Projected levels of suspended sediment are within recommended guidelines and will
not have an adverse effect the upstream and downstream migrations of eels and
lamprey.
Sea Angling
Sediment deposition and suspended sediment concentrations are predicted to be negligible
at recognised sea angling locations and outside of Sligo Harbour where all boat-based
fishing activity takes place.
There will be no adverse effects on sea angling.
7.7.4.2 Dumpsite Area
Based on the information generated by modelling of sedimentation and suspended sediment
loads at the proposed dumping site, the impacts of dredge spoil disposal on bottom
communities and fish have been discussed by Chapter 6.
North West Crab Fishery
The principal conclusions with regard to crab ecology and implications for the crab fishery
are:
x
Many sessile and some mobile species covered by the dumped material will be lost,
notably where the material settles deepest after each dumping event.
x
This may include crab although there is evidence to show that smothering is unlikely to
cause mortality in crabs, which are able to escape from under silt and migrate away
from an area where dumping is taking place.
x
Given the relatively small footprint of the dumped material, the immediate loss of habitat
to crustaceans will be negligible.
x
Given the relatively small area of impact relative to the surrounding habitats, there
should be no significant negative impact on the bottom communities in the general
Donegal Bay area.
x
The impacted seafloor will be re-colonised from the surrounding faunal community and
will integrate as part of the overall habitat.
x
Re-colonisation should take place within a relatively short period of time (12-18 months).
Although there will be loss of habitat in the immediate area of dumping, the area will
recolonise and recover within 12-18 months. This will not have any effect on the
productivity of the north Mayo crab fishery either in the short term or in the long term.
7-25
Other Fishery Activity
It is concluded that fish may have reduced feeding opportunities in the area of the dumpsite
due to short term habitat loss on the seabed and reduced productivity. However, fish in the
vicinity of dredge disposal operations will avoid areas affected by the dredge plume.
There will be no impact on pelagic or demersal fisheries in the area either in the short
term or in the long term.
7.8
MITIGATION MEASURES
7.8.1 Dredging Area
7.8.1.1 Water Quality Monitoring
A monitoring programme is recommended to take regular measurements of dissolved
oxygen (DO) and turbidity in Sligo Harbour during dredging operations. There parameters
should be recorded in the immediate area of dredging and at key locations in the navigation
channel and at shellfish aquaculture sites.
Turbidity is recorded in National Turbidity Units (NTU) and may be used as an indicator of the
concentration of Suspended Solids (SS). A programme of calibration linking Turbidity (NTU)
and SS (mg/l) should be carried out using solutions of known SS concentration made up
from samples of the sediments to be excavated.
Triggers levels should be established which, if exceeded, would lead to immediate
suspension of dredging until levels have recovered.
7.8.2 Dredge Disposal Site
7.8.2.1 Closure of site to fishing
The dumpsite and surrounding area to a radius of 1km should be closed to commercial
fishing activity during dumping operations. This will be to avoid any damage to or loss of
fishing gear.
7.8.2.2 ROV monitoring of seabed
ROV equipment should be deployed to verify settlement of dumped materials in the
designated area.
7.8.2.3 Water Quality Monitoring
A second monitoring programme is recommended for the dumpsite. This exercise would also
take regular measurements of dissolved oxygen (DO) and turbidity at the site and
surrounding area during dumping operations.
Triggers levels should be established for each parameter with readings to be taken along set
transects emanating from the edge of the site.
7-26
7.8.2.4 Crustacean Monitoring Programme
A crustacean monitoring programme is recommended for the dumpsite to determine any
impact on shellfish stocks and the recovery period – this should be based on the crab stock.
It is suggested that individual fishermen should be contracted to fish at pre-determined
locations in the region of the dumping site. Verification of fishing activity and catch would be
required. The programme should include baseline monitoring of the site prior to dumping and
resumed after dumping to examine recovery of the site.
7-27
7-28
8.0
Air and Climate
AIR AND CLIMATE
This chapter of the Environmental Appraisal Report describes the existing environment in
terms of climate and emissions to the air, with particular reference to dust and noise. An
assessment is provided of the likely impact on emissions to the air from the proposed
dredging and, where possible, mitigation measures are put forward to reduce the impact of
the scheme.
8.1
CLIMATE
The climate at Sligo is influenced mainly by its topography, being surrounded by relatively
high ground, and coastal situation. Ireland’s climate in general is defined as a “temperate
oceanic climate” and it experiences a lack of temperature extremes compared to other areas.
Summers are generally warm and winters are very mild. There is a regional variation, with
inland areas being cooler in winter and warmer in summer than their coastal counterparts.
8.1.1 Wind
As can be seen from figure 8.1, which shows a cumulative annual average of the wind
speeds and directions taken from the meteorological station at nearby Belmullet between
1957 and 2010, the prevailing winds at Sligo are from the south west. Wind blows most
frequently from the south west to west sector, while winds from the north and east occur
least often. In January, southerly and south-easterly winds are more prominent than in July,
which has a high frequency of westerly winds. Easterly and north easterly winds occur most
often between February and May and are commonly accompanied by dry weather.
Figure 8.1: Windrose for Belmullet Meteorological station 1957-2010
www.meteireann.ie (2011)
8-1
Air and Climate
8.1.2 Temperature
The dominant influence on Ireland's climate in terms of temperature is the Atlantic Ocean.
The waters around the coasts are remarkably warm, 7° to 8°C warmer than the average
global sea temperature at these latitudes, thanks to the warm North Atlantic Drift, the main
ocean current affecting Ireland (Met Éireann, 2011). Prevailing south westerly winds transfer
the heat from the sea to the land, thus creating a lack of temperature extremes when
compared to other areas of similar latitudes. Summer temperatures exceed 30°C usually
only once or twice every decade (though commonly reach 29°C most summers), while
severe freezes occur only occasionally in winter, with temperatures below í10°C being very
uncommon, and temperatures below freezing uncommon in many coastal areas. At the
Belmullet meteorological station, the coldest months are January and February, with average
maximum temperatures of around 8.2°C and the warmest month is August, where average
maximum temperatures are around 17°C. 30 year average sea temperatures (1961-1990),
measured at Malin Head, show average sea temperatures of 6.7°C in February rising to
14.6° in August.
Figure 8.2: 30 year monthly average temperatures (Belmullet) and sea temperatures
(Malin)
8.1.3 Precipitation
In Ireland, the main rain-bearing winds are from the south west, therefore tending to make
the western half of the country wetter. Rainfall in the west generally averages between 1,000
and 1,400 mm per year, however in mountainous districts rainfall can exceed 2,000mm per
year. The eastern half of the country is generally drier, averaging between 750 and 1,000
(mm) of rainfall annually (Figure 8.3).
8-2
Air and Climate
The wettest months in almost all areas are December and January. April is generally the
driest month generally across the country, but in some southern areas June is the driest.
Hail and snow contribute relatively little to the precipitation measured.
Figure 8.3: Met Éireann 1961-1990 mean annual average rainfall
The average annual rainfall for the 5km² area in which Sligo is located, is around 1193mm
per annum, with the wettest months occurring between October-January and May (Figure
8.4). On average, in Sligo the driest month is April, followed by June.
Figure 8.4: Met Éireann Average Monthly Rainfall for 5km² containing Sligo Harbour
8-3
Air and Climate
8.1.4 Potential Impacts on Climate
There are no significant long term gaseous emissions associated with the proposed dredging
which could impact air quality. The proposed dredging will therefore have no impact on the
climate either locally or regionally.
8.1.5 Potential Impacts on Air Quality
No disturbance of dry sediments will occur during the proposed dredging operations. Once
dredged, there will be no increase to the drying areas of the foreshore. The proposed
dredging will therefore have no impact on the air quality in Sligo Harbour.
8.2
NOISE
This section of the assessment will consider the potential noise impact of the proposed
dredging works at Sligo Harbour. The proposed works involve the dredging of sediments
from the navigation channel into Sligo Harbour and its transportation to an offshore dump site
some 34 nautical miles west of the docks. No rock breaking activities will be required.
Dredging will occur along the northern shore of Sligo Harbour, within the navigation channel
extending from Oyster Island to the Deepwater and Barytes jetties. There are a small number
of residential units located along this length of the coast, situated at varying distances from
the shore, the most proximate circa 150m from dredging activity.
Sligo Harbour is situated in an urban area; however, dredging activity will occur in close
proximity to residential properties that are situated within suburban and rural areas. The
dredging operations are expected to last for 4-6 months.
The location of the proposed dredging works is presented in Figure 8.5.
8.2.1 Existing Environment
It is submitted that the existing noise environment in the vicinity of the proposed works is
typical to that of a suburban coastal site, being shaped by the local activity and
environmental conditions. Previous surveys undertaken by this consultancy at various
coastal villages and harbours around Ireland indicate that background levels vary
significantly depending on weather conditions. Background levels are likely range from low
30’s dB LA90 to mid to high 50’s dB LA90 under high wind and rain. Ambient levels are likely
range from mid to high 30’s dB LAeq to low to mid 60’s dB LAeq, again dependant on weather.
8.2.2 Evaluation Criteria
Presently, in Ireland, there are no fixed noise limits for construction noise and the control of
such sources is outside the remit of the EPA. In general it is left to the discretion of the local
council authority and An Bord Pleanàla to determine if fixed limits are appropriate. Such
restrictions are rare, and there is little precedent. In Fingal Council Area discussions are
underway with the Construction Industry Federation to agree time limits of Monday to Friday
daytime, and Saturday morning, but with no restriction on noise levels. However a useful
8-4
Air and Climate
indication of potential impact can be gained by comparison with current practice in Northern
Ireland.
The impact of the short-term works associated with the site preparation and subsequent
construction will be assessed using BS5228 (2009), “Noise and Vibration Control on
Construction and Open Sites”.
Figure 8.5: Location of Dredging Area
8.2.3
Assessment of Temporary Construction Noise Impact
The nearest residential properties to the proposed dredging area are at least 150m from the
extents of the residential properties situated in the Ballincar area.
BS 5228 provides recommendations for temporary construction noise limits, based on an
assessment of the existing ambient noise levels within the vicinity of the works. The “ABC”
method, as found in BS 5228 Section E.3.2, provides an appropriate assessment method for
determining temporary construction noise level targets. The level is determined by rounding
the ambient noise level within the vicinity of the construction works to the nearest 5 dB. This
resultant level is then compared with Category A, B and C values. When this resultant level
is 5 dB less than Category A values, then noise limits should be set in line with Category A
values. When the resultant level is similar to Category A values then noise limits should be
set in line with Category B values. When the resultant level is similar to Category B values or
8-5
Air and Climate
higher, then noise limits should be set in line with Category C values. Table 8.1 below
outlines values for Categories A, B and C.
Table 8.1: Example Threshold of significant impact at dwellings
Assessment Category and Threshold Value
Period LAeq
Threshold Value, in Decibels (dB)
Night-time (23:00-07:00)
Category
A
45
Category
B
50
Category
C
55
Evenings and weekends
55
60
65
Daytime (07:00-09:00) and Saturdays (07:00-13:00)
65
70
75
Therefore, as it is expected that ambient levels at the most proximate residential properties
to the proposed dredging activity will be up to 65 dB LAeq, it would be deemed appropriate to
set construction noise target levels similar Category B.
8.2.4 Comment on Noise Associated with Dredging
With reference to BS5228, noise levels of dredging works are typically 96 dB LAeq at 10m,
however, manufacturers’ data suggests a sound power level of 109 dB Lw, which equates to
a sound pressure level of 81 dB LAeq at 10m. Measured data of cutter suction dredging
activity in Cork Harbour has resulted in an LAeq of 80 dB at 10m.
The DEFRA “Noise Database for Prediction of Noise on Construction and Open Sites”
indicates that a grab hopper dredging ship produces noise levels of 82 dB LAeq at 10m.
Measurement and assessment of specific “state of the art” dredging equipment (cutter
suction rig type) used at Cushendall (Co. Antrim) was conducted on 9 July 1999 by this
consultancy. During normal operations, dredging activity resulted in a specific activity level
of 49.4 dB LAeq at 108m (typically over hard ground or water). Assuming a point source, with
no soft ground absorption, this equates to 70 dB LAeq at 10m.
It can be seen that there is wide variation of noise level from dredging plant, dependant on
the specific plant used. However, typical levels are circa 82 dB LAeq at 10m and this value
will be used for assessment purposes.
Dredging activity will involve the removal of material from the bed of the channel, using a
dredging ship. The ship collects material, through either a chain and bucket system or cutter
suction system, until fully laden. The dredging ship will then steam to a location
approximately 34 nautical miles from the port, outside Donegal Bay, where the material is
discharged from the dredger. The dredging process within Sligo Harbour is expected to take
approximately 90 minutes per tide, with the majority of the remaining time during each tide
spent steaming to and from the material dumping location. Dredging activity will only occur
around the high tide, as at other times the water depth is insufficient for the dredging ship to
enter. Targets set with regard to BS 5228 refer to a 12 hour LAeq for daytime (07:00-19:00)
and an 8 hour LAeq for night time (23:00-07:00). Therefore, it will be necessary to include a
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Air and Climate
correction for on time, as dredging activity will only occur for a short period during daytime
and night time.
Dredging activity will occur, assuming an absolute “worst case” scenario, at circa 150m from
the most proximate residential properties at Ballincar. At all other times dredging activity will
occur at a greater distance from residential properties. Neglecting any ground absorption or
possible screening, but considering a point source, and assuming that dredging is at extent
of works:
Daytime Noise Impact
Dredging Activity Level
=
82 dB LAeq at 10m
Correction for “on time”
=
10 log (80/720)
=
-10 dB
Attenuation by Distance
=
20 log (150/10)
=
24 dB
=
48 dB LAeq, 12hr
Impact at Property (Ballincar)
It can be seen that dredging at the extent of works is within the maximum allowable daytime
exposure of 70 dB LAeq, 12hr for construction noise at the nearest properties. The majority of
dredging activity will occur at a greater distance, therefore it is predicted that the impact at
residential properties will typically be less than calculated above.
Due to time constraints during the construction process, and the dependency on suitable
weather conditions for dredging, it may be necessary for these works to continue throughout
the night. In these circumstances the predicted impact at the most proximate residential
property is as follows:
Night time Noise Impact
Dredging Activity Level
=
82 dB LAeq at 10m
Correction for “on time”
=
10 log (80/640)
=
-9 dB
Attenuation by Distance
=
20 log (150/10)
=
24 dB
=
49 dB LAeq, 8hr
Impact at Property (Ballincar)
It can be seen that dredging at the extent of works is within the maximum allowable night
time exposure of 50 dB LAeq, 8hr for construction noise at the nearest properties. The majority
of dredging activity will occur at a greater distance, therefore it is predicted that the impact at
residential properties will typically be less than calculated above. Therefore, it is possible for
dredging to continue throughout the night for the majority of works, while remaining within
target levels, using appropriate plant.
8-7
8.2.5
Air and Climate
Mitigating Measures for Temporary Construction Works
8.2.5.1 Monitoring
Given the limited impact it would not be appropriate to require regular noise monitoring of the
site. However, occasional measurement of noise levels generated using a Type 2 or better
sound level meter should be conducted to check on the continuing impact of the works.
8.2.5.2 Responsible Person
It is often recommended that the appropriate party should appoint or delegate a responsible
person who will be present on site and who will be willing to answer and act upon queries
from the local public.
8.2.5.3 Night Works
Due to the essential nature of the works, dredging activity must occur within close proximity
to residential properties. It is also likely that dredging activity will occur during night time
hours. Due to the 4-6 month timescale of the works, it is recommended that local residents
are duly notified of intended works in close proximity to their residences, particularly during
night time hours as this will help to alleviate tensions and reduce potential for noise complaint
related to the dredging activity.
8.2.6
Conclusions
The potential noise impact from the proposed works associated with the dredging of Sligo
Harbour has been assessed and appropriate evaluation criteria and target noise levels have
been ascertained.
It has been shown that noise from short-term construction works can be controlled to within
reasonable and previously applied noise level limits at any noise sensitive locations. Some
mitigating measures have been included to provide additional instruction to the contractor.
Other sources of noise effects are not likely to be significant. On completion of the project, no
significant noise impact from the works will occur.
8-8
9.0
Material Assets
MATERIAL ASSETS
This chapter of the Environmental Appraisal Report describes the existing infrastructure of
the settlements around Sligo Harbour in terms of fresh water and waste water treatment,
roads, services and communication. It provides an assessment of the impact of the proposed
dredging and, where possible, puts forward mitigation measures to reduce or eliminate the
impact.
9.1
INFRASTRUCTURE
9.1.1
Water Supply
Historically, there have been issues in the supply of drinking water in the Sligo region,
however since the late 1990s Sligo County Council has carried out very significant
investment in water infrastructure, including the implementation of the Sligo and Environs
Water Supply Scheme.
The Sligo and Environs Water Supply Scheme was designed to provide for the domestic,
agricultural and industrial potable water requirements for Sligo and its outlying regions and
meet the highest possible standards in accordance with all national and E.U. legislation,
thereby;
x
x
x
x
providing adequate water supply for fire fighting within the Borough.
reducing leakage in the existing water supply distribution system and maximising the
benefit of existing resources.
providing adequate water supply to eliminate the severe disruption to supply to
consumers; and
eliminating restrictions on residential, commercial and industrial development.
The scheme provides for the domestic, agricultural and industrial water requirements of Sligo
City and its outlying regions, such as Ballincar, Rosses Point, Strandhill and Ballintogher.
The majority of the drinking water supply for Sligo town and its environs is sourced from
Lough Gill, supplemented by a gravity supply from Kilsellagh, located to the north of the city.
Two water treatment plants are in operation treating water from Lough Gill; Cairns Hill and
Foxes Den with a third plant at Kilsellagh. These three plants have been (or are in the
process of being) upgraded to facilitate the improved treatment and overall quality of the
water supply.
A further five regional water supply schemes supply drinking water to the wider areas of
County Sligo.
However, a number of rural dwellings and small communities throughout Sligo do not have
the benefit of a public mains water supply system. These dwellings rely on group schemes
and individual well supplies. It is an objective of the County Council to ensure that all rural
9-1
Material Assets
water supplies comply with the EC (Drinking Water) (No.2) Regulations 2007 (Sligo County
Council, 2005).
Many private water users rely on groundwater sources that are vulnerable to contamination.
Therefore the protection of underlying aquifers is important for the environmental quality of
rural water supply. As described in Chapter 10.2 of this Report, “Hydrogeology” no impacts
to groundwater supplies are anticipated as a result of the dredging.
The proposed dredging will not pose any demands on or alterations to the drinking water
supply for Sligo town and its environs, beyond providing potable water for the crew on board
the dredging vessel. No impacts are anticipated and no mitigation is therefore required.
9.1.2
Sewerage Infrastructure
The provision of wastewater treatment infrastructure is imperative to facilitate the economic,
social, and physical development of the county and to support settlement growth. In addition,
the continued improvement and provision of this infrastructure is necessary to meet the
requirements of the Urban Wastewater Treatment (Amendment) Regulations 2004.
The Sligo Main Drainage Scheme, commissioned in 2009, has provided Sligo City and
surrounding areas with adequate treatment and drainage capacity to serve up to 50,000 PE
(population equivalent), thereby allowing for future development and growth. The Waste
Water Treatment Plant (WWTP) is sited on the area of reclaimed land adjacent to Sligo Port
at Finisklin which was used for the previous disposal of dredged material from Sligo Harbour
during maintenance dredging in the 1980s and early 1990s.
Figure 9.1: Sligo WWTP at Finisklin
9-2
Material Assets
Prior to the construction of the WWTP, sewage from Sligo town was discharged untreated
into Sligo Harbour.
The treatment works have a capacity to treat waste water for a combined domestic and
commercial population equivalent of 50,000 and it has the capabilty to be expanded to
80,000 at a future date. The facility serves not only Sligo City, but also in the future
surrounding areas including Ballincar, Cregg, Rosses Point Carrowroe and Cummeen will be
connected to the scheme.
In addition to meeting the Urban Wastewater Treatment Regulations, the scheme has also
significantly improved water quality within Sligo Harbour and its surrounding waters, thus
also improving the water quality status in terms of the EU Water Framework Directive, the EU
Bathing Waters Directive, the EU Habitats Directive, and the EU Shellfish Waters Directive.
The proposed dredging at Sligo Harbour will not generate any waste water discharge into the
sewerage infrastructure, therefore it will not pose any impacts or create any additional
pressure on to the provision of waste water treatment services in Sligo. The International
Convention for the Prevention of Pollution from Ships (MARPOL) Annex IV “Prevention of
Pollution by Sewage from Ships” contains requirements to control pollution of the sea by
sewage; the discharge of sewage into the sea is prohibited, except when the ship has in
operation an approved sewage treatment plant or when the ship is discharging comminuted
and disinfected sewage using an approved system at a distance of more than three nautical
miles from the nearest land. Sewage which is not comminuted or disinfected must be
discharged at a distance of more than 12 nautical miles from the nearest land. The dredger
will adhere to these regulations and will not discharge foul waste or bilge water into Sligo
Harbour.
9.1.3
Surface Water
The IPCC (Intergovernmental Panel on Climate Change) predicts that due to climate change
Ireland’s west coast will suffer increased rainfall intensity and more numerous and intense
storms. The increase in rainfall, particularly of high intensity, is likely to result in increased
river, land and associated flood plain water levels. River catchment areas that are influenced
by tidal effects are likely to be impacted more frequently due to combined effects.
The Sligo and Environs Development Plan 2010 – 2016 lists a number of flood protection
aims and policies which should be taken into consideration when planning new development.
Surface water drainage design should reflect the likely increase in intensity and frequency of
rain storms. Outfall levels should take cognisance of potentially higher receiving water
levels. Future potential additional discharges into receiving water that are themselves tidelocked should be analysed and risk-assessed taking cognisance of existing predictions.
SEDP Flood prevention policies:
x P-FP-1 Restrict development within 50 m of ‘soft’ shoreline.
x P-FP-2 Ensure that no further reclamation of estuary land takes place.
x P-FP-4 Assess all coastal defence measures for environmental impact.
9-3
x
Material Assets
P-FP-6 Land uses shall not give rise to increases in the run-off characteristics above
those that currently exist.
The proposed dredging of the navigation channel will not pose any additional pressures on
the area of Sligo town in terms of increasing flood risk.
9-4
9.1.4
Material Assets
Mechanical and Electrical Services
The construction of the new waste water treatment plant at Finisklin has precipitated
significant upgrades to the electricity and telecommunications infrastructure network within
the docklands area (Pat Doyle, Sligo Co. Council pers.comm.). Reinforcement of the
national grid to the western side of Sligo town has taken place and high speed broadband
now exists at the site. It is hoped that these enhancements will assist in attracting new
investment to the area, such as attracting manufacturing industries to the existing Sligo
Business & Technology Park at Finisklin as a secure power supply and high speed
telecommunications links are highly desirable for manufacturers. Should the former landfill
site become approved for re-development in the future, this ground will also have high value
for industrial or business development.
The proposed dredging of the navigation channel at Sligo Harbour will pose no significant
impact to the existing mechanical and electrical services within the docklands area or the
wider Sligo area. All communications and infrastructural connections beneath the channel
should be buried at depths substantially below the dredging level, however the chosen
contractor should have due regard to cables or pipelines beneath the channel and ensure
that the position and depth of these has been correctly identified.
9-5
9.2
Material Assets
TRAFFIC
This section will concentrate on the impact of the traffic generated by the dredging process
on the access to the harbour and also to the adjacent National Primary Route.
9.2.1 Background
The proposed dredging site is located within Sligo Harbour and as part of a recent feasibility
study carried out by Sligo County Council, it has been established that the materials cannot
be disposed of or re-used onshore, therefore it is proposed to dredge the material and
directly transport the material to an offshore dump site, approximately 34 nautical miles from
the harbour.
9.2.2
Existing Baseline Conditions
9.2.2.1 Overview of Existing Industry
The existing harbour area is a busy industrial area, which includes several large oil
distributions yards, building supplier depots and various other industrial warehouses. From a
traffic perspective, this generates substantial movements throughout the day, many of which
are HGVs. The harbour itself is also a working port with ships importing and exporting goods
of both local and national importance including mainly scrap metal, coal, timber and fish
meal. Given the nature of the shallow shipping lane and the available tidal range the number
of ships visiting the port is low. Table 9.1 below, reproduced from the information in Chapter
1, illustrates the docking pattern of Sligo Port over the last number of years and shows that in
recent years the number of ships docking and their associated tonnages have remained fairly
constant therefore causing minimal net increase in associated traffic.
Table 9.1: Docking Pattern at Sligo Harbour
Year
No of Ships
Tonnage
2011
21
49,000
2010
24
52,000
2009
25
53,000
2008
25
41,000
2007
26
46,000
2006
23
43,000
9-6
Material Assets
9.2.2.2 Existing Access Routes
The existing access to the harbour is on Deep Water Quay, which leads onto the N4 via
either Ballast Quay or Finisklin Road. While both routes comprise of a carriageway
approximately 8m wide and include footpaths along both sides. Ballast Quay Road is the
shorter route of the two and would provide a more suitable route as Finisklin Road includes a
school and a railway bridge with limited headroom. In consultation with Sligo County Council
Road Design Office, it was confirmed that the Ballast Quay Road would normally be the
primary route and Finisklin Road would only act as an overflow should the junction of Ballast
Quay and the N4 become congested. These conditions would indicate that the Ballast Quay
Road would offer the most favourable route to the National Primary Road and we will
continue our assessment on this basis. Figure 9.2 below shows a drawing indicating the
relationship of these junctions.
Figure 9.2
Junctions in Vicinity of Port
9.2.2.3 Existing National Primary Road and Access Junctions
The junction of the Ballast Quay Road with the N4 is a signalised crossroads comprising the
through bound N4 to the north and south, Ballast Quay Arm to the west, and Custom House
Quay Arm to the east. The N4 Southbound Arm includes two lanes; one for left turns into
Custom House Quay and ahead movements while the other is a dedicated right turning lane
into Ballast Quay. The N4 Northbound Arm comprises of three lanes; the right hand lane
catering for traffic turning into Custom House Quay, the middle lane for ahead movements
9-7
Material Assets
and the left lane for both ahead movements and for traffic turning into Ballast Quay. Custom
House Quay serves several car parks and provides some limited access to the town centre
and this approach has one lane for all left, right and ahead manoeuvres. The Ballast Quay
Road Arm approach includes three lanes, one dedicated to each of the left, right and ahead
movements. The junction is also well served by pedestrians crossings dedicated crossing
points on all arms.
The access to the harbour is via a priority junction of the Ballast Quay Road and the
Deepwater Quay Road. All arms of the junction are approximately 10m in width and existing
radii are measured at approximately 10m and while good quality footpaths are provided no
crossing points are included.
9.2.2.4 Summary of Existing Network
Good provision currently exists for movements through the signalised Ballast Quay Road/N4
junction with dedicated lanes for all movements through the busiest arms and efficient
pedestrian links that work with traffic flow. A high quality carriageway and footpath links this
junction to the harbour access at Ballast Quay Road/Deepwater Quay Road, a priority
junction with good vehicular capacity but limited pedestrian crossing points.
9.2.3 Existing Flows taken from Model
A Paramics model built for Sligo Town shows 2008 traffic flows between the harbour site and
the N4 national primary route via the Deepwater Quay and the Ballast Quay as per Table 9.2
below. National Traffic Forecasts published by the NRA show an average traffic increase of
5.1% between 2008 and 2010. However our assessment will be more robust if we are to
assume the same traffic figures as 2008; circumstances which many would regard more
likely than recent NRA forecasts.
Table 9.2: Existing Traffic Flows along Primary Route
Route
Deepwater Quay
Ballast Quay
Peak Period
Arrivals
Departures
Two Way
Flow
AM
145
70
215
PM
54
123
177
AM
302
349
651
PM
192
340
532
Deepwater Quay/Barytes Jetty experiences a two way flow of 215 in the AM Peak and 177 in
the PM Peak, with Ballast Quay accommodating a two way flow of 651 in the AM Peak and
532 in the PM Peak. We will use this as a basis for our assessment of how the local
infrastructure copes with the increase in traffic generated by the dredging proposals.
9-8
9.2.4
Material Assets
Predicted Impacts During Dredging
As part of a feasibility report carried out previously by Sligo County Council, it was concluded
that the dredged material could not be reused or disposed of in a suitable manner and so it
was agreed that it should be directly shipped to an off-shore dumping site.
On the basis of the feasibility report it is assumed that the dredging operation will occur
locally and that no material will be transported outside the harbour site. For this reason this
assessment assumes that the only arrivals and departures generated will be the additional
workers required to carry out the works.
For this dredging scheme, it currently remains undecided as to what type of dredging vessel
is to be used; a trailer suction dredger, which aspirates the sediment from the bed, or a
backhoe dredger which excavates the sediment from the bed. For either method, the vessel
is to be deployed on a 24 hour basis with a crew of four/five working in shifts. For each tide
(approx 12.4 hours) the vessel will be dredging for approx 70-80 minutes through high tide as
the channel is too shallow to enter/exit during other periods of the tide. It will spend the
remainder of the shift sailing to and from the dump site, 34 nautical miles offshore, outside
Donegal Bay. An onshore crew of two/three crew will be required to supervise works and
administer offshore operations.
9.2.4.1 Generated Traffic
As part of any Traffic and Transport Assessment, it is normal to establish the arrivals and
departures of the proposed development using TRICS. This investigates arrivals and
departures of sites with a similar land use and so gives trips that are representative of the
proposed site. However; the trips generated by TRICS usually apply to permanent proposals
and not temporary dredging practices such as this. For this reason it is necessary to apply
the number of operatives required for the works and apply trip rates accordingly.
For the purposes of this assessment we have discussed the scope of the works with the
marine consultants as described above and established that an additional workforce of seven
will be required to crew the dredger, four/five on board the dredger and two/three on shore. It
is probable that all crew would live on the dredging vessel over the course of the works and
that any journeys would be taken in a communal van/mini-bus provided by their employers.
This would suggest that traffic movements generated by the dredging works would be
minimal; however in the next chapter we will discuss this in more detail and consider some
assumptions that will ensure a robust assessment.
9.2.5
Mitigation Measures
As referred to previously in Section 9.2.4.1, there will be a limited number of additional
vehicles generated by the site during dredging operations; however this does not allow us to
disregard the effect that alternative travel measures will have on mitigating this traffic or our
9-9
Material Assets
need to provide a thorough assessment. We have considered the sustainable travel methods
available and assessed their suitability.
9.2.5.1 Walking/Cycling
As mentioned earlier, the harbour can be easily accessed from the N4 through good
pedestrian links already provided along both Ballast Quay Road and Deepwater Quay Road.
This principle in supported by the Sligo and Environs Development Plan 2010-2016, which
contains proposals to extend the pedestrian link into the town centre by providing a
waterfront walkway from Hyde Bridge to Hughes Bridge (bridge at N4).
9.2.5.2 Public Transport
At present there are no bus routes that serve the harbour and within the current
Development Plan there are no plans to extend these services. While a railway line does
exist in the harbour area it is only used for freight and not passenger traffic. Therefore public
transport cannot be used as a viable option for travelling to and from the site.
9.2.5.3 Shared Transport
As mentioned previously the most likely mitigation measure to be employed is shared
transport. It is assumed that all of the operatives on the dredger will work for the same
company and that transportation would be provided as part of their arrangement. However
for the purposes of this study and to ensure a robust assessment, we will assume that each
employee will use their own personal mode of transport to the site. (i.e. by car)
9.2.6
Conclusions
The normal criteria to follow when studying network and junction capacity is in line with the
NRA “Traffic and Transport Assessments Guidelines”, which states that the threshold at
which Transport Assessments should be carried out are 10% for normal junctions and 5%
where congestion exists.
9.2.6.1 Comparing Existing and Generated Flows
Table 9.3 below shows the traffic flows received from the Sligo Town Paramics Model
mentioned previously. This assessment has compared the existing arrivals and departures
with associated generated trips in the relevant period.
9-10
Table 9.3
Material Assets
Percentage increase during dredging operations
Deepwater Quay
9.2.7
Ballast Quay
AM
PM
AM
PM
2008 Arrivals
145
54
302
192
2008 Departures
70
123
349
340
Proposed 2010
Arrivals
7
0
7
0
Proposed 2010
Departures
0
7
0
7
% INCREASE
(ARRIVALS)
4.8%
0%
2.3%
0%
% INCREASE
(DEPARTURES)
0%
5.7%
0%
2.1%
Percentage Increase
As shown in Table 9.3, the percentage increase in traffic arising from the predicted trips
generated by the dredging operation remain within the 10% threshold specified by the NRA.
Indeed for Ballast Quay, the percentage increase does not extend beyond the more onerous
5% threshold.
9.2.7.1 Residual Impacts
On the basis of the findings above and the recommendations of the NRA “Traffic and
Transport Assessment Guidelines” this assessment shows that the traffic generated by the
dredging works is within the recommended thresholds. We are satisfied that the works will
not have any adverse effect on the local infrastructure. Indeed the trips are likely to be further
reduced due to the fact that the dredging crew are to reside within the vessel and that all
travel will be via a communal van/mini-bus. This will further reduce the arrivals/departures
and will probably reduce the impact on both the Deepwater Quay Road and the Ballast Quay
Road below the 5% threshold.
9-11
Material Assets
9-12
Geology & Soils
10.0 GEOLOGY AND SOILS
This chapter of the Environmental Appraisal Report describes the natural characteristics of
the site in terms of geology, hydrogeology and the nature of the marine sediments. The
geological regime has been established from the results of sediment testing and geophysical
surveys, supported by a review of geological mapping records. An assessment is made of
the likely impact of the proposed scheme on these natural resources and, where necessary,
mitigating measures are put forward to reduce the impact of the proposed development.
10.1
SOLID GEOLOGY
The bedrock geology of County Sligo has been mapped by the Geological Survey of Ireland
and is published as Sheet 7 of the 1:100,000 Solid Geology Field Series (Sligo-Leitrim).
The geology of County Sligo is complex and indirectly spans more than 1,700 million years.
The geological aspect of the site relative to its regional and local setting is discussed below
and illustrated in Figure 10.1.
The geology of Sligo-Leitrim can be sub-divided into five major divisions for descriptive
purposes:
x
Metamorphic rocks of Proterozoic and partly lower Palaeozoic age (schist and gneiss),
dating from about 1700 to 500 million years, exposed in the Ox Mountains,
x
Sedimentary rocks, often strongly folded and mildly metamorphosed (red sandstone), of
lower Palaeozoic to Devonian age, from 500 to about 360 million years,
x
Almost unfolded sedimentary rocks of Carboniferous age (limestone, limestone/shale
and sandstone), deposited during the period from 355 to 320 million years ago,
x
The post-Carboniferous, intrusive igneous rocks (granite) about 65 million years old; and
x
The Quaternary unconsolidated sediments, younger than 1.6 million years.
Site Location
Figure 10.1: Site Location
10-1
Geology & Soils
10.1.1 Regional Geology
Sligo Harbour is within a zone where mainly Carboniferous era limestone (mainly
Ballyshannon Limestone and Dartry Limestone) and shale rocks are exposed at the surface
(shown in shades of blue/grey in Figure 10.2), although a small inlier of Proterozoic age
rocks outcrops on Rosses Point, at the northern boundary of Sligo Harbour (shown in
yellows, greens and browns on Figure 10.2). This inlier is a site of Geological Interest
highlighted by the GSI in their consultation response, as it exposes the contact between the
Slishwood formation (CZ on Figure 10.2) and the Dalradian (LS on Figure 10.2).
The southern shores of Sligo harbour, as well as Coney Island and Oyster Island are
comprised of Glencar Limestone. The Carboniferous rocks represent a period, between
around 355 and 310 million years ago, where Ireland was gradually submerged by rising sea
levels (Macdermot et al, 1996). This marine transgression took millions of years to envelop
Ireland, spreading northwards from Cork. On land, rivers deposited sand and silt, now
represented by grey sandstones and siltstones. In the shallow nearshore waters, muddy
limestones and shales were formed. Further offshore, pure limestones were formed. Low
hills lay between river valleys or plains; the higher of these were never covered by river
sediments, but were eventually covered by the rising sea. Where this happened, limestones
rest directly on pre-Carboniferous rocks, such as at Rosses Point.
Figure 10.2: Local Geology, from GSI 100k mapping
10-2
10.2
Geology & Soils
HYDROGEOLOGY
Groundwater in Ireland is protected under European Community Legislation (Groundwater
Directive 80/68/EEC) and national legislation, namely the Local Government (Water
Pollution) Acts of 1977 and 1990, which make it an offence to pollute groundwater.
Groundwater is water found below the surface of the earth, often occurring in natural
reservoirs in permeable rock layers. Bedrock formations or sand and gravel deposits which
yield significant quantities of water are called aquifers. The type of rock affects the volume
and chemistry of the water. The limestone rock types around Sligo and Rosses Point have
been identified as aquifers of both local and regional importance, as can be seen in Figure
10.3.
Figure 10.3: Bedrock Aquifers
The Water Framework Directive (WFD) is a European Union directive which commits
European Union member states to achieve good qualitative and quantitative status of all
water bodies by 2015. Waterbodies can relate to surface waters (these include rivers, lakes,
estuaries [transitional waters], and coastal waters), or to groundwaters.
For the purposes of the WFD, Ireland has been divided into six River Basin Districts (RBDs).
For each RBD, a River Basin Management Plan (RBMP) has been prepared. The RBMP
contains information on the status, risks, and objectives for each water body within the RBD.
For each water body, measures are proposed achieve “good status” in water bodies that are
of lesser status at present and to retain good status or better where such status presently
exists.
10-3
Geology & Soils
The body responsible for monitoring groundwater quality is the Environmental Protection
Agency.
10.2.1 Potential Impacts to Groundwater
A number of activities can have an impact on groundwater resources, including:
x
Excessive pumping e.g. from wells for water supply
x
Saline intrusion (risk of over-abstraction in coastal areas pulling sea water into the
groundwater body
x
Pollution from nutrients, e.g. nitrates and phosphates
x
Pollution from chemicals
Figure 10.4: Groundwater Status (2010)
The groundwater bodies in proximity to the proposed dredging area are Rosses Point, Sligo
and Drumcliff-Strandhill. The Sligo and Drumcliff-Strandhill groundwater bodies have
achieved “good” status during their last assessment for the Water Framework Directive. The
Rosses Point groundwater body failed to achieve “good”, or even “moderate” status (Figure
10.4), failing in its chemical status due to poor results in monitoring for loadings of reactive
phosphates and nutrients. Nutrients can be discharged into the aquatic environment through
wastewater from households and industry or by loss of nutrients from agriculture or fish
farming. Agriculture is the main source of nitrogen loading and a major source of
phosphorus loading, although much phosphorus also comes from point sources and sparsely
built-up areas.
10-4
Geology & Soils
All three groundwater bodies are currently assessed as being “not at risk” of saline intrusion.
10.2.2 Predicted Impacts to Groundwater.
The proposed dredging will only remove sediments from the bed of the navigation channel.
No removal of bedrock is envisaged with this scheme, therefore there is no risk of creating a
new pathway for saline intrusion to occur. There is no risk of increasing nutrient loadings as
a result of the proposed dredging.
No mitigation measures are therefore required, in terms of groundwater.
10.3
GROUND CONDITIONS
10.3.1 Dredging Area Sediment Physical Properties
In order to gain knowledge of the physical properties of the sediments along the navigation
channel and enable an appropriate side slope design, Priority Geotechnical were
commissioned to carry out a marine investigation to obtain sediment cores along the
shipping channel at Sligo Harbour.
Figure 10.5: Vibrocore sample stations
10-5
Geology & Soils
The investigation comprised of vibrocore sampling to 3.0m depths at twelve locations (Figure
10.5) and took place in April 2010. Stations 1, 3 and 12 had more than one vibrocore taken.
The fieldwork was carried out in general accordance with BS 5930 (1999) “Code of Practice
for Site Investigation” and Part 9 of BS 1377 (1990), “Method of Tests for Soil for Civil
Engineering Purposes, in situ Tests”.
A Geo-corer 3000 was used to obtain the 100mm diameter continuous core, sediment
samples (Figure 10.6).
Figure 10.6: Vibrocorer
The sediment conditions were such that there were 3 distinct sediments identified: silt, sand
and coarse to fine shell.
Inside the Port of Sligo, VC01 and VC02 indicated slightly sandy silt and very clayey gravel
sediments to a depth of 1.0m below the existing bed level. Location VC03 indicated slightly
silty sandy shell sediment to 1.0m depth. The shell fragments accounting for 70% of the
material by mass. It should be noted that these stations are outside the proposed dredging
area.
Of the 8 stations inside the dredging area, locations VC04 to VC05 indicated sandy silt to
3.0m depth. At VC06 the silt containing 42% shell fragments was underlain by silty sand with
11% shell content by mass. Locations VC07 and VC08 identified slightly sandy silt with
some shell fragments, 3% to 15% to 3.0m depth. The silt was of very high plasticity. At
locations VC09 to VC11 slightly silty sand with up to 14% shell fragments was identified to a
depth of 3.0m. VC12 was characterised by silty very sandy shell to 2.5m depth.
10-6
Geology & Soils
The sediments are summarised in the following table, Table 10.1. The full report on the
sediment properties is included in Appendix 6A.
Table 10.1: Summary of Sediment Conditions
Stratum Encountered
Range of sediment thicknesses
Locations
Slightly sandy/ gravelly SILT
1.0m to 3.0m
VC01*, VC02*, VC07
and VC11
Slightly sandy SILT with shell
1.0m to 3.0m
VC06 and VC08
Sandy SILT
1.0m
VC04
Slightly silty sandy SHELL
1.0m to 2.5m
VC03, VC12* and
VC12.1*
Very silty SAND
2.0m to 3.0m
Slighty silty SAND
2.0m to 3.0m
VC04, VC05 and
VC06
VC09 , VC10 and
VC11*
*Station location outside of final dredging area
10.4
OFFSHORE DISPOSAL SITE
10.4.1 INFOMAR Survey
Donegal Bay is one of the areas which has been surveyed for the INFOMAR project (The
INtegrated Mapping FOr the Sustainable Development of Ireland’s MArine Resource).
INFOMAR is a joint venture between the Geological Survey of Ireland and the Marine
Institute. The programme is a successor to the Irish National Seabed Survey (INSS) and
concentrates on creating a range of integrated mapping products of the physical, chemical
and biological features of the seabed in the near-shore area. Consultation was therefore
held with the Geological Survey of Ireland (GSI) regarding the proposed offshore disposal
site in addition to the dredging area.
The GSI responded that the dumping site at the outer edges of Donegal Bay is located
behind (west of) an important moraine (Figure 10.7), approximately running NE-SW, which,
along with indentified currents, would act as a natural barrier to the re-deposition of any
dredged material towards Donegal Bay and Sligo Bay. No particular forms of life (cold water
corals and others) were identified in that area on the seabed during the 2008 INFOMAR
survey.
10-7
Geology & Soils
Offshore Disposal Site
Figure 10.7
GSI/Marine Institute INFOMAR Moraine Shaded Relief Image
Reproduced from http://www.infomar.ie/ (2011)
The moraine is a glacial deposition feature which takes the form of a large ridge running
roughly north to south offshore from Rossan Point, Co. Donegal. Moraines are composed of
sediments which were eroded and transported by a large ice sheet from the Northwest Ice
Dome. After the Last Glacial Maximum (~14,000 years ago) there was a general trend of
retreat of ice. Evidence of this is seen in the lower ridge features in the top right corner of the
image above, showing the episodic retreat of the ice sheet depositing glacial sediments as it
went. However, at some stage it is thought that the ice retreat was slowed/stopped or
readvanced allowing large amounts of sediment to be deposited in one ridge that eventually
formed this spectacular moraine feature, now lying in 60 metres of water. (GSI, 2010)
In addition to the detailed bathymetry data collected by the INFOMAR project, the GSI also
were able to collect additional information on the seabed properties by analysing the strength
of the acoustic signal returned from the seafloor. This is known as backscatter. Differing
seafloor types, such as mud, sand, gravel and rock will have different backscatter values
depending on the amount of energy they return to the receiving equipment. Rocky areas will
typically have high returns, while soft sediments like mud are more likely to absorb energy
and have low backscatter returns. These differing values were used to generate a greyorder image (i.e. dark for high returns, bright for low returns) of the seabed which can be
used to examine the nature of the seafloor. The backscatter results are correlated with
sediment grab samples also taken from the seabed during the survey, to build a more
accurate picture of the physical properties of the seabed.
10-8
Figure 10.8
Geology & Soils
GSI Backscatter Image of Dumpsite
The GSI returned backscatter and ground truthing information on the seabed in the vicinity of
the proposed dump site area:
x
x
x
x
The dark part in the centre of Figure 10.8 labelled “gravel” represents the moraine;
The closest sample (blue dot) from the proposed dump site (6km) is made of coarse
sand and gravel, so it is anticipated that the proposed dump site would have the same
substrate;
The mixed dark and pale grey is identified as fine sand with shells (as the higher
acoustic reflectivity is due to a biological component (mainly understood as shell hash
accumulated by currents) and it is likely that the seabed in this area is a diverse habitat,
no cold water corals though as it is not deep enough and they grow on more rocky
substrates)
Any pale grey area is made of fine sand.
10-9
Geology & Soils
10.4.2 Field Surveys
10.4.2.1
Physical properties of the dump site sediments
In addition to the desktop survey of the data available from INFOMAR, two visits were made
to the proposed dump site, at spring tide and neap tide, to recover sediment samples from
the proposed disposal area for granulometric analysis and chemical testing as well as the
collection of benthic faunal information.
Figure 10.9
Grab Sample Stations January/February 2011
Grab samples were recovered from four stations within and adjacent to the proposed dump
site and were subject to analysis.
The results of the granulometric analysis carried out on the 4 sediment samples are included
as Appendix 6B while Table 10.2 presents a summary of these results. In general, the
sediments collected in and around the dumpsite (Stations 1-3) were typically made up of fine
sand with varying amounts of coarse sand and gravel. This corresponds well with the
properties of the sediment to be dredged. It can be seen on the backscatter image in Figure
10.9 that these stations fall on pale grey areas, which is consistent with the descriptions
provided by the GSI.
In their survey design, the Marine Insitute requested that a sample be taken from a station
located approximately 1km remote from the dump site (Station 4). The sediment collected
from this station, located approximately1.5 km south west of the site, was coarser in nature
with a high proportion of coarse sand. It can be seen in Figure 10.9 that this station is within
10-10
Geology & Soils
a darker coloured area of the backscatter image, again consistent with the GSI’s description.
This station will not be within the main deposition area and is unlikely to be affected by the
dumped sediments.
Table 10.2
Station
Results of the granulometric analysis on the dump site sediments
Gravel
(>4 mm)
C. Sand (1
– 4mm)
M. Sand (0.5–
1mm)
Fine Sand (0.0630.5 mm)
Silt/Clay
(<0.063mm)
1
0
0.4
0.7
96.0
2.8
2
0
3.1
0.6
94.9
1.4
3
0
0.2
1.8
97.0
1.0
4
9.5
70.8
16.3
3.3
0
Table 10.3
Physical properties of the dump site sediments
Station
ID
Colour
Smell
%
Water
1
Grey
brown
none
21.7
2
Grey
brown
none
19.6
3
Grey
brown
none
28.6
4
Grey
brown
none
16.3
10-11
10.4.2.2
Geology & Soils
Chemical properties of the dump site sediments
In accordance with the EPA’s Dumping at Sea Licence Application Guidance (2010),
samples were recovered from the proposed offshore dump site and were subjected to
chemical analysis. As the proposed dumpsite is a new site, these samples provide the EPA
with a baseline which will aid in considering the impacts of using the site should any future
applications be made.
Sediment samples were taken at the locations outlined in Figure 10.9 by means of a 0.1 m²
Day grab. It was intended to take a single grab at three stations along the southwest-north
east axis of the dumpsite and a fourth approximately 1 km from the dumpsite in the direction
opposite to the residual current for sediment analysis. However, bottom type dictated where
it was possible to take these grabs, which returned the locations as outlined in Figure 10.9.
When samples were returned from each station, notes were logged on sediment type,
amount, colour, smell and any other information that was considered relevant. A sample of
surface sediment was taken from the centre of the grab and placed in a suitable cleaned
container. All sampling jars were marked externally with date, station number, sample
number and survey reference number and placed in a cooler box.
The sampling parameters were set following consultation with members of the Marine
Licensing Vetting Committee (MLVC). Although the MLVC no longer directly assess
dumping at sea licence applications, a number of its members are on the EPA advisory
committee. The results of the sediment chemical testing are presented below.
Table 10.4 Proposed Dumpsite Baseline Sediment Testing Results
St1
St2
St3
St4
CRM
Carbon, Organic (%)
0.94
0.570
0.47
3.57
0.524
Mercury (mg/kg)
0.007
0.005
0.003
0.001
0.0866
Aluminium (mg/kg)
28300
28200
24700
19800
65800
Arsenic (mg/kg)
4.15
5.10
5.64
64.8
21.1
Cadmium (mg/kg)
0.145
0.158
0.209
0.088
0.216
Chromium (mg/kg)
272
304
693
21.4
89.0
Copper (mg/kg)
555
628
669
2.72
36.7
Lead (mg/kg)
11.7
11.0
11.4
15.5
21.7
Lithium (mg/kg)
13.8
12.7
8.48
11.6
70.7
Nickel (mg/kg)
184
223
447
7.54
42.4
Zinc (mg/kg)
99.7
109
112
22.5
156
Dibutyl Tin (ȝg/kg)
9.00
<3
656
Tributyl Tin (ȝg/kg)
<3
<3
478
CaCO3 (mg/kg)
3.60
3.78
3.03
3.42
0.013
Aldrin (ȝg/kg)
<1
-
-
<1
17.8
DDE-pp (ȝg/kg)
<2
-
-
<2
21.3
DDT-op (ȝg/kg)
<1
-
-
<1
19.0
10-12
Geology & Soils
DDT-pp (ȝg/kg)
<2
-
-
<2
19.2
Dieldrin (ȝg/kg)
<3
-
-
<3
21.6
Endrin (ȝg/kg)
<2
-
-
<2
24.3
HCH-alpha (ȝg/kg)
<1
-
-
<1
22.4
HCH-beta (ȝg/kg)
<1
-
-
<1
23.3
HCH-delta (ȝg/kg)
<1
-
-
<1
21.1
HCH-gamma (ȝg/kg)
<1
-
-
<1
22.3
Hexachlorobenzene
(ȝg/kg)
<1
-
-
<1
24.4
Hexachlorobutadiene
(ȝg/kg)
<1
<1
24.0
Isodrin (ȝg/kg)
<2
-
-
<2
18.0
TDE-pp (ȝg/kg)
<1
-
-
<1
23.3
PCB28 (ȝg/kg)
<0.1
-
-
<0.1
4.48
PCB52 (ȝg/kg)
<0.1
-
-
<0.1
5.56
PCB101 (ȝg/kg)
<0.1
-
-
<0.1
5.16
PCB118 (ȝg/kg)
<0.1
-
-
<0.1
4.28
PCB138 (ȝg/kg)
<0.1
-
-
<0.1
3.60
PCB153 (ȝg/kg)
<0.1
-
-
<0.1
5.52
PCB180 (ȝg/kg)
<0.1
-
-
<0.1
3.31
Hydrocarbons, total
(mg/kg)
4.95
-
-
0.08
1.43
10.4.3 Dumpsite Sediments Properties Conclusions
The sediments at the proposed dumpsite are typically made up of fine sand with varying
amounts of coarse sand and gravel. The sediments are brown or grey/brown in colour with
no particular smell. Contaminant analysis of sediments was undertaken at four stations
within and adjacent to the dump site to provide a baseline record of sediment chemistry.
Disposal of the dredged material at the proposed dump site will pose no significant impact to
the physical or chemical properties of the bottom sediments at this site.
10-13
Geology & Soils
This page has been left intentionally blank.
10-14
Coastal Processes
11.0 HYDRODYNAMIC MODELLING
Hydrodynamic modelling was undertaken to investigate the impact of the dredging
operations on Sligo Harbour. The modelling examines the effect of the dispersion and fate of
material put into suspension during the period of the dredging operations.
11.1
COMPUTATIONAL MODEL
OPERATIONS (5,500m³)
OF
WATER
INJECTION
DREDGING
Hydrodynamic modelling was undertaken to investigate the impact of the dredging
operations on Sligo Harbour. The modelling examines the effect of the dispersion and fate of
material put into suspension during the period of the dredging operations.
11.1.1 Modelling Software
The computational models used in this study were based on the MIKE 21 coastal process
software which has been developed by the Danish Hydraulics Institute. The modules of this
coastal process modelling system used in this study comprised:
x
2D hydrodynamic flow models
x
Particle tracking models
11.1.2 Hydrodynamic Flow Model
The main hydrodynamic flow model used in the study was a 2D MIKE21 nested HD flow
model consisting of a 30m grid outer model and a finer 10m grid inner model. The extent of
the nested flow model is shown in Error! Reference source not found. below.
11.1.2.1
Dredged Spoil Dispersal Model
The dredged spoil disposal modelling was undertaken using the MIKE 321npa model. This is
a particle tracking model that uses the hydraulic flow regime from the MIKE21 nHD model to
simulate the transport and fate of material discharged to the water column. The model can
include variable graded material and takes effect of re-erosion of deposited sediment so it is
particularly suitable for the simulation of the disposal of dredged spoil.
11-1
Coastal Processes
Figure 11.1: Extent of 30 and 10 metre grid nested flow model
11.1.3 Bathymetry
The bathymetry for the model studies was taken from very detailed LiDAR and multi-beam
hydrographic surveys of the entire model area undertaken by the Geological Survey of
Ireland in 2008 under the INFOMAR project. These surveys comprised some 46 Gigabytes
of xyz data. A narrow beam hydrographic survey was undertaken of c.850m of the
navigation channel leading to the Deepwater Jetty in October 2011 (Figure 11.2) to provide
accurate data on the quantity of material to be dredged.
11-2
Coastal Processes
Figure 11.2: Extent of LiDAR Bathymetry and 2011 Bathymetric Survey
11.1.4 Model Calibration
The models were calibrated against flow measurements undertaken in December 2009 using
two ADCP current meters, one deployed to the west of Deadman's Point and the other in the
channel to Drumcliff Bay. The model and current meter velocities were compared for tidal
conditions with the same tidal range and the model results were found to be consistent with
the field measurements.
11.1.5 Model Simulations
11.1.5.1
Tidal Flow Modelling
Model Tidal Flow Regime
The tidal flow modelling was undertaken for a whole month of tides based on a typical period
31 January 2003 to 2 March 2003. The fresh water flow into Sligo harbour was set at 14.7
cumecs which was derived from the annual average flow for the catchments feeding into the
Garavogue River. The tidal curve at Oyster Island for the model period is shown in Figure
11.3.
11-3
Coastal Processes
Figure 11.3: Tidal curve for 1 month simulation period.
The tidal modelling was undertaken for the existing bathymetry and for the bathymetry with
the proposed dredged channel completed. Typical flow patterns are shown in Figure 11.4
and Figure 11.5; which illustrate mid flood and mid ebb tides respectively around Sligo
harbour for a spring tide.
Figure 11.4: Typical flow patterns in Sligo harbour - flood tide
11-4
Coastal Processes
Figure 11.5: Typical flow patterns in Sligo harbour - ebb tide
11.1.6 Dredging Plume Simulation Modelling
11.1.6.1
Dredging Programme
The dredged plume modelling simulations were undertaken to provide information on the
dispersion and fate of dredged material discharged to the water column during the water
injection dredging of some 5,500 cubic metres of material required to clear the approach
channel to the Deepwater jetty and remove pockets of sediment from the berths at both the
Deepwater and the Barytes jetties.
The dredging will focus on 5 target sites within the dredging area outlined, as shown in
Figure 11.6, where the channel depth has become dangerously shallow.
A conservative approach has been taken to calculate the dredging impacts, using the “worst
case” impacts.
General information on the water injection dredging process has been obtained from
dredging contractors Van Oord, who have substantial experience in this field.
It is proposed that dredging will take place over a period of spring tides. The water depth
and current velocities in the channel are such that the dredger will only be able to work for
approximately 4.5 hours of every tidal cycle. Dredging operations will only occur on the
ebbing tide in order to assist with the travel of the mobilised sediment away from the port
area.
The quantities involved (5,500m³) are relatively small. It is thought that the dredger will be
able to remove around 1,000m³ of sediment per tide, therefore it will take only around 5 or 6
11-5
Coastal Processes
tides to complete the operations. In order to take account of the length of time it may take for
particles put in to re-suspension during subsequent tides to settle out, the model has been
run for 28 days to present a complete picture of final dispersion and settlement patterns.
11.1.6.2
Flow Model Data
The dredging plume modelling was undertaken using the M321 npa particle tracking model
which simulates the transport and deposition of material discharged into the water column.
The model uses the data from the tidal model simulation as the basic hydrodynamic input to
the simulations.
11.1.6.3
Sediment Composition
As part of the sampling regime for the larger capital and maintenance dredge project
proposed within Sligo Harbour, 12 No. samples from the bottom sediments along the entire
5.2km length of the navigation channel were collected for physical, chemical and radiological
testing. The full results of this testing are presented in Attachment C.1 and C.2.
The location of the sampling stations in relation to the dredging area is shown in Drawing 4
It can be seen that Station Dr-5 is within the proposed Water Injection Maintenance Dredging
Area, whilst Stations Dr-4 and Dr-6 are approximately 150m upstream and downstream of
the Dredging Area respectively.
11-6
Coastal Processes
Figure 11.6: Target areas (A-E) for maintenance dredging by Water Injection Dredging
Table 11.1: Dredging Area Sediment Samples – Descriptions
Station Location
Colour
Smell
%
ID
Water
Grey/brown
none
66.6
Dr-4
Channel
c. 200m south Mud
east of
dredging area
boundary
WGS84
54° 16' 52.79"
N
8° 29' 21.3" W
ITM
568140,
837059
11-7
Dr-5
Inside
dredging area
Coastal Processes
Grey/brown
Muddy sand
none
54.4
Grey/brown
Muddy/sand
none
64.3
WGS84
54° 17' 1.93" N
8° 29' 32.86"
W
ITM
567932,
837343
Channel
c. 200m north
west of
dredging area
boundary
Dr-6
WGS84
54° 17' 9.89" N
8° 29' 41.78"
W
ITM
567773,
837590
Table 11.2: Dredging Area Sediment Samples – Granulometry Results
Station
Dr-4
Dr-5
Dr-6
Gravel
(>4 mm)
0
0
0.5
C. Sand
(1 – 4mm)
2.1
1.0
0.4
M. Sand
(0.5– 1mm)
5.4
2.5
0.3
Fine Sand
(0.063-0.5 mm)
52.8
83.4
85.4
Silt/Clay
(<0.063mm)
39.6
13.1
13.4
The information from the three samples shows that the material to be dredged is
predominantly a fine grey silty sand.
Water Injection Dredging puts the seabed layer into suspension by injecting water into the
subsoil, thus fluidising it. This fluidised bottom layer, the thickness of which (typically
between 1m and 3m) is highly sensitive to both the soil parameters and the distance
between the injector pipe and the seabed ("stand-off distance"), then behaves as a density
current.
The low injector pressure (approx.1 bar) and keeping a small stand-off distance are key
factors in minimising turbidity. The optimum stand-off distance, which depends upon the
settled sediments’ particle size distribution and permeability, is often determined through
11-8
Coastal Processes
practical experience. The properties of the induced fluid mud layer depend on a large
number of factors, but of prime importance are the particle size and viscosity of the sediment.
The fate of the material being put into suspension by the dredger has been assessed using
the Mike 321 npa model. The model simulates the fate of the material from the dredger by
releasing particles into the water column at a source 0.5m above the bed and tracking each
particle throughout the simulation process. A range of grain sizes have been used in the
model, in order to cater for the sediment grading of the dredged material. The grading used
for the main source was based on the grading in the PSA results from the bed material
samples. This source had the distribution of grain size shown below.
Grain Dia mm % Occurrence
11.1.6.4
0.375
0.187
0.090
0.050
6
62
20
7
0.030
5
Dredging Simulations
The dredging programme and tidal conditions were as noted in the above sections.
Dredging operations were assumed to be undertaken over 5 consecutive tides.
The simulations for the dredging were run for the full 28 day tidal sequence to give the
overall pattern of dispersion and deposition including the effects of particle re-suspension
from the whole of the dredging operation.
11.1.7 Results of the Dredging Simulations
11.1.7.1
Sediment Deposition
The results of the water injection dredging simulations are shown graphically by a series of
model output diagrams. The figures show the sediment deposition depths during dredging
and at the completion of the dredging, as well as the peak and average envelope values for
the suspended sediment concentrations throughout the dredging.
The maximum deposition envelope diagram (Figure 11.7) represents the maximum value
that occurred at each grid point in the model at any time during the simulation period, even if
the period of the peak value is very short.
The maximum peak sediment deposition depth in mm can be roughly calculated by dividing
the kg/m² by a figure of 1.65. This shows that in the areas of the harbour coloured green, the
maximum peak deposition depth is c.4mm – 6mm. However, in some areas around the
training walls, peak deposition could reach c.24mm to 48mm.
11-9
Coastal Processes
However, it should be noted that these peak values are typically of a very short duration and
tend to occur as current speeds drop during slack tide. The material may then be raised into
suspension again and moved further from the dredging area as the tidal currents pick up
during the next tide.
This re-suspension will cause the final settlement pattern to be more defined (Figure 11.8),
with the dredged material settling around the training wall, in sheltered areas on the northern
shore of Cartron Marsh and some of being swept out of the harbour to settle on the Bungar
Bank and offshore from Rosses Point.
The pattern of residual sediment deposition following the completion of the dredging is
shown in Figure 11.8.
In general, deposition depths in these areas will be beneath 3.0mm with only very limited
areas receiving more than 10mm of deposition. Overall the amount of sediment deposition in
the harbour area on completion of water injection maintenance dredging operations is
considered to be a localised temporary impact of moderate negative magnitude1.
1
When using the NRA EcIA criteria for assessing impact magnitude
11-10
Coastal Processes
Figure 11.7: Peak sediment deposition depths in Sligo Harbour during water injection
dredging operations
(also showing sensitive areas/monitoring stations – See 1.1.9)
11-11
Coastal Processes
Figure 11.8: Final sediment deposition depths on completion of water injection
dredging operations
(also showing sensitive areas/monitoring stations – see 1.1.9)
11-12
Coastal Processes
11.1.8 Suspended Sediments, pH and Dissolved Oxygen
Dredging also has the potential to cause temporary increases to the amount of suspended
sediments held in the water column.
The hydrodynamic model was also used to predict the duration and extent of the changes to
suspended sediments within the sensitive environment of Sligo Harbour.
In accordance with the monitoring requirements of Council Directive 79/923/EEC, on the
quality required of shellfish waters, and Council Directive 91/492/EEC, which sets down the
health conditions for the production and placing on the market of live bivalve molluscs, the
Marine Institute collect water and shellfish samples from major shellfish growing areas at
regular intervals and analyses them for physicochemical parameters, trace metal levels and
chlorinated hydrocarbon concentrations. Sampling results were obtained from the Marine
Institute for the shellfish beds within Sligo Harbour for use as a baseline indicator of
suspended sediments.
Table 11.3 below shows suspended sediment concentration values measured in 2009 -2011
at this water quality sampling location. The station is also shown as Station Mon-3 in Figure
11.10.
Table 11.3: Measured suspended sediment in Sligo Harbour
by Probe
PSAL
TEMP
(PSU)
(degC)
Date
Actual
Lat
Actual
Long
Sample
Depth
(m)
D
OXY
(%)
pH
(sc)
03/12/09
54.2893
-8.5238
0.5
99
8
16.19
8.2
16/12/09
54.2893
-8.5238
0.5
96.3
8.11
26.5
7.79
20/01/10
54.2893
-8.5238
0.5
109
8.23
13.03
7.05
16/02/10
54.2893
-8.5238
0.5
108
8.45
23.7
7.57
23/03/10
54.2893
-8.5238
0.5
103
8.32
31.69
9.7
14/04/10
54.2893
-8.5238
0.5
135
8.48
16.65
13.1
17/05/10
54.2893
-8.5238
0.5
124
8.31
31.85
13.7
23/06/10
54.2892
-8.5287
0.5
140
8.68
28.12
18.1
13/07/10
54.2892
-8.5242
0.5
130
8.42
32.22
17.7
23/08/10
54.2898
-8.5252
0.5
102
8.34
28.46
17
20/09/10
54.2883
-8.5263
0.5
143
8.8
25.32
16.4
21/10/10
54.2893
-8.5232
0.5
114
8.11
30.11
13.2
13/06/11
54.2895
-8.5240
0.5
110
8.27
28.74
18.9
11/07/11
54.2895
-8.5242
0.5
131
8.15
24.5
18.8
14/12/11
54.2893
-8.5238
0.16
108
7.97
25.58
5.3
TURB
(%)
22.9
CPHL
(ȝg/l)
By Lab
SUSP COLOR
(mg/l)
(sc)
25.6
18.6
12
13.6
<2
6.6
72
7.9
8
<4
<2
30.2
136
(Source: Marine Institute data request)
It can be seen that measured values vary widely depending on the date when the
measurements were taken (from <2 to 72 mg/l). The sediments disturbed by the dredging
process in the navigation channel will cause temporary increases in suspended sediment
concentration within Sligo Harbour during dredging operations.
11-13
Coastal Processes
As stated above, actual dredging operations will only occur for around 4.5 hours per tide
(12.4 hours) and dredging should be substantially completed over a period of 5 tides. The
dredging should be timed to occur only during the early part of the ebbing tide, in order to
give the mobilised particles the greatest opportunity of being transported a sufficient distance
downstream.
The influence of the dredging may continue for several more days, as the sediments
removed from the site are brought into re-suspension during subsequent tides, therefore the
simulations were run for a total of 28 days.
The average value envelope for the suspended sediment concentrations throughout the
dredging is presented below in Figure 11.9.
On this figure the green areas show mean suspended sediment concentrations of 80100mg/l, rising to 200-300mg/l in the yellow areas immediately surrounding the dredging
area during the water injection maintenance dredging campaign.
In practice however, dredging does not cause a continuous increase above background for
the duration of operations but rather causes the suspended sediment concentration to rise
rapidly shortly after active dredging begins during each tide, achieving a peak around the
period of slack water, before returning back to background or near-background values before
the next dredging session begins on the next tide. Following completion of dredging, the
displaced material lying on the seabed will be swept up into suspension during subsequent
tides as current speeds increase, settling out temporarily as speeds drop again during slack
water before being picked up again and moved on during the next tide.
11-14
Coastal Processes
Figure 11.9: Mean suspended sediment concentrations during water injection
dredging operations (for bottom 0.5m of water column)
(also showing sensitive areas/monitoring stations – see 1.1.9)
11-15
Coastal Processes
11.1.9 Sensitive Areas
During the ecological baseline studies (see Appendix D.1(viii)), four areas which have the
potential to be vulnerable to adverse impacts of the dredging activities were identified.
These areas are indicated on Figure 11.10.
Figure 11.10: Location of Identified Sensitive Areas and Timeseries Locations
Google aerial photo dated 2006 © Google/Digitalglobe/NASA
Area 1: The area surrounding Cartron Marsh and Standalone Point, where dredging activity
has the potential to cause impacts on important bird feeding areas by affecting forage or prey
species.
Area 2: an environmentally important habitat of seagrass (Zostera) which may be vulnerable
to smothering caused by the dredging.
Area 3: encompassing the main area of commercial and natural shellfish beds, including the
large mussel bank in the centre of the harbour.
Area 4: a commercial clam production area
In order to portray in a more appropriate manner the magnitude and duration of the changes
to the suspended sediment concentrations within the harbour, a time series showing the
peak concentration of suspended sediments in the bottom 0.5m of the water column during
and after dredging as well as sedimentation depths has been produced for 4 points:
Point Mon-1 (Cartron Marsh)
Point Mon-2 (Southern Cummeen Strand)
Point Mon-3 (Commercial mussel bed and Marine Institute baseline monitoring station)
Point Mon-4 (Commercial clam bed)
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Coastal Processes
The results are presented only for the bottom 0.5m as it is changes to this part of the water
column that will have greatest impacts on the shellfish and intertidal/subtidal bird prey and
forage species which are present within the harbour.
Figure 11.11 to Figure 11.14 shows the time series of peak suspended sediments and peak
sedimentation for the duration of the proposed water injection dredging campaign at each of
the four stations within Sligo Harbour.
0.5m and Sedimentation for Carton Marsh Area during dredging campaign (Point Mon1)
It can be seen in Figure 11.11 that the area most affected, with the highest peak values of all
of the time series recorded is in Cartron Marsh, due to it being the closest station to the
dredging area. The red lines show the predicted peak suspended sediment concentrations
in the bottom 0.5m of the water column while the blue lines show the peak depth of sediment
settling out (depths in mm being approximately equivalent to the kg/m² divided by 1.65). It
can be seen that during dredging operations, which will occur for 3 days over the first spring
tide period in the model, the peak suspended sediment levels increase rapidly with
increasing current speed during each tide. The highest peaks, occurring on 3 of the spring
tides, reach levels of around 4-5g/l, but more typical peak values are below 1.5g/l.
The temporary rises in suspended sediment concentration typically last up to 3 hours, but
with the peak values (seen as “spikes” on Figure 11) lasting for a much shorter period of only
11-17
Coastal Processes
15-30 minutes. The period between peaks (tides), when concentrations return back to
baseline, or near baseline, levels will be much longer (around 9 hours). The short duration of
the peak concentrations is confirmed when we revisit the mean suspended sediment
concentration values for the time series (Figure 9) which shows a mean concentration of
60mg/l throughout the duration of the timeseries at Point Mon-1.
It can be seen from the blue lines in the Carton Marsh time series that when the current
speeds drop, the material settles out with the greatest peak sedimentation depth of around
13mm occurring during the tide immediately following the completion of the dredging
operations. After 5 days, the depth of sediment being settled out during the slack tide is in
the order of 2.5mm. It can be seen that during the neap tides the current speeds are not
sufficiently strong to pick up the deposited material during each tide and it remains in place
for several days, however during the next spring tide the stronger current speeds pick up
more sediment, causing a brief rise in both suspended sediments and subsequent
settlement, before the material is finally flushed out of the area at the end of the spring tide,
around 20 days after dredging operations began.
The effects of the water injection dredging at Cartron Marsh can therefore be predicted to be
moderate negative in magnitude but temporary in duration.
Figure 11.12: Time series showing peak Suspended Sediment Concentration in
bottom 0.5m and Sedimentation for Southern part of Cummeen Strand during
dredging campaign (Point Mon-2)
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Coastal Processes
At Point 2, on the southern shore of Cummeen Strand, it can be seen in Figure 11.12 that it
takes until the next spring tide before the sediment mobilised by the dredging reaches the
site. Peak suspended sediments at this site are modelled to reach around 600mg/l on the
highest spring tide following the dredging, with more typical peak values below 100mg/l. The
average suspended concentration at this point across the modelling period is less than
20mg/l. In between tides, sedimentation will be barely perceptible with levels of around
0.4mm occurring during slack tide. The impact arising from this small increase in suspended
sediment and sedimentation is predicted to be neutral and temporary.
Figure 11.13: Time series showing peak Suspended Sediment Concentration in
bottom 0.5m and Sedimentation near commercial shellfish farm during dredging
campaign (Point Mon-3)
At Point 3, which is located at the Marine Institute monitoring station close to the commercial
shellfish farm on Cummeen Strand, small peaks in suspended sediment (red lines) can be
seen during the spring tides (Figure 11.13). These peak increases will be in the order of 50250mg/l with a small number of tides where material in suspension will settle out temporarily
in this site. Average suspended sediment concentrations throughout the modelled period at
this site are below 20mg/l. The depths of sedimentation are not predicted to be significant,
with temporary sedimentation depths in the order of 0.4 to 0.8mm (blue line) predicted. The
impact arising from this small increase in suspended sediment and sedimentation at Point 3
is predicted to be neutral and temporary.
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Coastal Processes
Figure 11.14: Time Series showing peak Suspended Sediment Concentration in
bottom 0.5m and Sedimentation for commercial clam farm during dredging campaign
(Point Mon-4)
At Point 4, the commercial clam farm to the west of Cummeen Strand, the effects of the
dredging will be barely perceptible (Figure 11.14). During the spring tide following the
dredging, very small peak suspended sediment concentrations of less than 60mg/ will be
experienced at this site. The predicted impact at this site is anticipated to be neutral and
temporary.
11.1.10
Conclusion
It can be seen from the modelling results that significant elevations in suspended sediment
within Sligo Harbour caused by the dredging only occur in the immediate vicinity of where the
dredger is working, and within the confines of the navigation channel.
The areas in which sensitive habitats have been identified, at Cartron Marsh, southern
Cummeen Strand and at the nearby aquaculture sites will experience very short term
increases in suspended sediment concentrations in the lowest 0.5m of the water column and
small amounts of temporary sedimentation, particularly during the water injection dredging
phase. However, the majority of the dredged material will eventually settle out around the
training walls or will be transported out of the harbour during the following spring tide where
the material will settle out on the sand banks at the entrance to Sligo Harbour and the
residual effects will not be significant.
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Coastal Processes
The chemical analysis of the proposed material to be dredged has shown that it has a
relatively low organic content. The risk of the dredging causing significant impacts to
dissolved oxygen levels in the harbour is therefore considered to be low. Mitigation
measures including real time monitoring of suspended sediment levels and dissolved oxygen
levels are described in Chapter 7, Fisheries and Aquaculture.
11-21
11.2
COMPUTATIONAL
MODEL
OPERATIONS (250,000M³)
Coastal Processes
OF
CONVENTIONAL
DREDGING
11.2.1 Introduction
area during the dredging operations. The modelling was used to examine the effect of:
1. The change in channel bathymetry on the tidal flows and water levels, and
2. The dispersion and fate of material spilled during the period of the dredging
operations.
11.2.2 Computational Models
11.2.2.1
Modelling Software
The computational models used in this study were based on the MIKE 21 coastal process
software which has been developed by the Danish Hydraulics Institute. The modules of this
coastal process modelling system used in this study comprised:
x
2D hydrodynamic flow models
x
Particle tracking models
11.2.2.1.1 Hydrodynamic Flow Model
The main hydrodynamic flow model used in the study was a 2D MIKE21 nested HD flow
model consisting of a 30m grid outer model and a finer 10m grid inner model. The extent of
the nested flow model is shown above in Figure 11.1 in Section 11.1.3.
Figure 11.15: Extent of 30 and 10 metre grid nested flow model
11.2.2.1.2 Dredged Spoil Disposal Models
The dredged spoil disposal modelling was undertaken using the MIKE 321npa model. This is
a particle tracking model that uses the hydraulic flow regime from the MIKE21 nHD model to
simulate the transport and fate of material discharged to the water column. The model can
include variable graded material and takes effect of re-erosion of deposited sediment so it is
particularly suitable for the simulation of the disposal of dredged spoil.
11.2.2.2
Bathymetry
The bathymetry for the model studies was taken from very detailed LiDAR and multi-beam
hydrographic surveys of the entire model area undertaken by the Geological Survey of
Ireland in 2008 under the INFOMAR project. These surveys comprised some 46 Gigabytes
of xyz data.
11-22
11.2.2.3
Coastal Processes
Model Calibration
The models were calibrated against flow measurements undertaken in December 2009 using
two ADCP current meters, one deployed to the west of Deadman's Point and the other in the
channel to Drumcliff Bay. The model and current meter velocities were compared for tidal
conditions with the same tidal range and the model results were found to be consistent with
the field measurements.
11.2.3 Model simulations
11.2.3.1
Tidal Flow Modelling
11.2.3.1.1 Model Tidal Flow Regime
The tidal flow modelling was undertaken for a whole month of tides based on a typical period
31 January 2003 to 2 March 2003. The fresh water flow into Sligo harbour was set at 14.7
cumecs which was derived from the annual average flow for the catchments feeding into the
Garavogue River. The tidal curve at Oyster Island for the model period is shown in Figure
11.3 above in 11.1.4.
The tidal modelling was undertaken for the existing bathymetry and for the bathymetry with
the proposed dredged channel completed. Typical flow patterns are shown in Section 11.1.5
in Figure 11.4 and Figure 11.5; which illustrate mid flood and mid ebb tides respectively
around Sligo harbour for a spring tide.
11.2.3.1.2 Impact of Dredging on Tidal Flow Regime
The impact of the proposed dredging of the channel to the deepwater quay was assessed in
terms of changes to overall tidal levels and tidal flow velocities.
Figure 11.16 – Figure 11.18 show a comparison of the tidal curves at Sligo town for the
existing situation (blue) and with the post-dredging channel in place (red). It can be seen in
Figure 11.16 that during a neap tidal cycle there is an imperceptible difference in water levels
between the existing and post-dredging channels.
The overall average tidal curve shows a minor reduction in water level during low tide, but no
increase in water level at high tide. During an extreme spring tide, there is a slightly greater
reduction in the water level during low tide. The proposed dredging will not result in any
increase in water level at high tide, therefore the proposed dredging of the channel will not
cause any increase in the risk of flooding in Sligo from high spring tides.
The reduction in water level during an extreme low spring tide is caused by the removal of
the bar within the shipping channel by the proposed dredging. At present, this bar slows
down the passage of water exiting the channel at low tide, causing some water be retained
or pooled behind it. If the bar is dredged, the water will be able to drain more freely at low
tide, thus causing lower water levels and possible drying out of the channel upstream of the
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Coastal Processes
bar at extreme low spring tides. As can be seen on Figure 11.18 this drying will last for a
maximum of 2 hours.
Figure 11.16: Comparison of existing and dredged channel tidal curves at Sligo (neap
tide)
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Coastal Processes
Figure 11.17: Comparison of existing and dredged channel tidal curves at Sligo
(overall average)
Figure 11.18: Comparison of existing and dredged channel tidal curves at Sligo
(extreme spring tide)
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Coastal Processes
The impact of the proposed dredging on the flow regime in Sligo Harbour has been assessed
by comparing the mean and peak flow velocities for both flood and ebb tides. Different plots
have been used to highlight the magnitude and location of changes in the tidal current
velocities which are predicted to occur due to the proposed dredging of the channel into
Sligo's deep water quay. The analysis has been shown only for spring tides, as the
differences will be more pronounced during spring tides compared to the effect at neap tides.
Figure 11.19 and Figure 11.20 show the difference in the mean tidal velocity for both flood
and ebb spring tides. In these diagrams, the difference in the tidal velocity is calculated by
comparing the average tidal velocity over the flood or ebb period for the model with the
dredged channel in place and subtracting the equivalent flows for the model with the existing
bathymetry. It will be seen from these diagrams that the difference in the mean velocities is
generally very small (less than 0.1 m/s) and the changes are restricted to the area around
the channel and the northern section of the harbour area.
Figure 11.19: Difference in mean spring flood tide velocity - proposed minus existing
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Coastal Processes
Figure 11.20: Difference in mean spring ebb tide velocity - proposed minus existing
Figure 11.21 and Figure 11.22 show the difference in the peak tidal velocity for both flood
and ebb spring tides. The diagrams show the difference in the maximum tidal velocity that
occurs at any time during the period at every grid cell within the model area. It should be
noted that these peak velocities will not necessarily occur at the same time in each part of
the harbour area. In these diagrams the difference in the tidal velocity is calculated by taking
the peak tidal velocity during the flood or ebb period for the model with the dredged channel
in place and subtracting the equivalent flows for the model with the existing bathymetry.
Figure 11.21: Difference in peak spring flood tide velocity - proposed minus existing
11-27
Coastal Processes
Figure 11.22: Difference in peak spring ebb tide velocity - proposed minus existing
As with the mean tidal flow difference plots, it can be seen that the impact of the dredging on
the peak tidal flow speeds is generally insignificant, except in the area of the channel itself
where increases of up to 0.4m/s may be experienced in localised areas. Peak speeds in the
area north of the navigation channel may be slightly decreased by around 0.1m/s.
In summary, the tidal flow modelling indicates that while the proposed dredging will lower the
level of the low water spring tides in the channel at Sligo, the high spring tide level will be
unaffected by the proposed dredging works. The dredging will have an insignificant effect on
the current flows in the harbour area except in the area of the channel and adjoining northern
section of the harbour. The secondary main harbour drainage channel, to the south of middle
bank, experiences a drop in peak current speeds of up to 0.2 m/s whilst parts of the
navigation channel have increased speeds of up to +0.4 m/s in very localised areas with
more typical peak speed changes in the order of -0.05 to +0.05m/s.
11.2.3.2
Dredging Plume Simulation Modelling
11.2.3.2.1 Dredging Programme
The dredged plume modelling simulations were undertaken to provide information on the
dispersion and fate of dredged material discharged to the water column during the dredging
of some 250,000 cubic metres of material required to deepen the approach channel.
The precise methodology for dredging will not be known until a dredging contractor has been
appointed, therefore a conservative approach has been taken to calculate the dredging
impacts, using the “worst case” impacts. The water depths in the existing channel are such
that it is likely that the dredger will have to dig its way upstream and that it will only be able to
dredge during the upper half of the tidal cycle. Thus for the modelling simulations it has been
assumed that the dredging programme will be organised to dredge during periods when the
water levels are above mid tide level and sail to and from the disposal area during the lower
11-28
Coastal Processes
half of the tidal cycle. For the purposes of the simulation it was assumed that it will take four
months to undertake the dredging work. This gives an average dredging quantity of about
2,100 m³ per day and an excavation rate of about 175 m³ per hour while the dredger is
working in the channel. These figures represent a “worst case” scenario using a stationary
dredger and more than one transportation barge to transport the dredged material to the
proposed dump site. In the event of the dredging operations using a mobile dredger or
single barge, the dredging will take place over a longer period of time with lesser quantities of
suspended sediments being released and the impacts on the environment will be reduced.
11.2.3.2.2 Flow Model Data
The dredging plume modelling was undertaken using the M321 npa particle tracking model
which simulates the transport and deposition of material discharged into the water column.
The model uses the data from the tidal model simulation as the basic hydrodynamic input to
the simulations.
The tidal models for both the existing channel and with the proposed dredged channel in
place were used for the dredging simulation modelling. The hydrodynamics with the existing
channel were used for the dredging of lower section of the channel, i.e. seaward of the end
of the rebuilt training wall, while the hydrodynamics with the proposed deepened channel in
place were used for the simulations of the dredging of the upper channel section up to the
deep water quay. The 30 day tidal curve used in the simulations is shown in Figure 11.23.
Figure 11.23: Tidal curve for hydrodynamic regime used in the dredging simulations
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Coastal Processes
11.2.3.2.3 Bed sediments and dredging losses
As noted in Chapter 10 “Geology and Soils”, a number of bed samples were analysed as part
of the study. The information from the various samples shows consistently that the material
to be dredged is predominantly a fine grey silty sand. Even though there is an increase in
the shell and gravel fraction further downstream in the channel, only the finer fractions are
put into suspension in the water column during dredging, with the heavier fractions settling
out within a few metres of the dredger.
The losses from the dredger have been assessed using on on-site measurements made
during the construction of the Denmark – Sweden fixed link tunnel and bridge and by
reference to data contained in “Scoping the Assessment of Sediment Plumes from Dredging”
CIRIA 547. As the exact type of dredger which will undertake the work is unknown at this
stage, a conservative approach to the losses of material to the water column was taken.
Thus the total losses to the water column were assumed to be 3% of the dredged volume
represented by a 2% source at 2.5 metre below the surface and a 1% source at the surface.
The Mike 321 npa model simulates the fate of the loss of material from the dredgers by
releasing particles into the water column and tracking each particle throughout the simulation
process. A range of grain sizes have been used in the model, in order to cater for the
sediment grading of the dredged material. The grading used for the main source located at
2.5 metres below the surface was based on the grading in the PSA results from the bed
material samples. This source had the distribution of grain size shown below.
0.375
0.187
0.090
0.050
6
62
20
7
0.030
5
The source at the surface had a finer grading, as the losses at the surface come from
overspill or washout of finer fractions of the dredged material. The grading of the source at
the surface used in the study was as follows:
0.090
45
0.050
30
0.030
25
11.2.3.2.4 Dredging Simulations
The dredging programme and tidal conditions were as noted in Sections 11.2.3.2.1 and
11.2.3.1.1 above. The dredging of the channel was considered in two halves, i.e. a lower
section comprising the channel up to the commencement of the rebuilt training wall on the
western side of the channel and an upper section consisting of the section of the channel
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Coastal Processes
beside the rebuilt training wall, up to the deep water berth. Each section of the channel was
assumed to take 2 months to dredge giving a total of 4 months dredging. This is the worst
case scenario, assuming the dredging would be done as quickly as possible. In reality the
dredging could take longer in which case the scale of the impact on the harbour will be
reduced.
In the simulations the dredger was assumed to work its way up the channel from seaward
dredging half the channel width at a time. The sources in the model were moved to keep
track of the dredger with breaks in the sequence while the dredger was travelling to and from
the dump site.
The simulations for the lower and upper channel sections were each run for the 30 day tidal
sequence and then results for each area multiplied up by two to match the appropriate
dredging period. Finally, the results of the dredging of the two channel sections were
combined to give the overall deposition from the whole of the dredging operation.
11.2.3.2.5 Results of the Dredging Simulations
The results of the dredging simulations are shown graphically by a series of model output
diagrams. The figures show the sediment deposition depths at the completion of the
dredging as well as the average value envelopes for the suspended sediment concentrations
throughout the dredging of each of the channel sections. The maximum sediment deposition
depth envelopes are also shown for the deposition of sediment during the dredging of each
of the channel sections.
The maximum deposition envelope diagrams represent the maximum value that occurred at
each grid point in the model at any time during the simulation period, even if the period of the
peak value is very short. The average concentration envelope is the average value at each
grid cell in the model throughout the period when the cell is wet. In these diagrams the period
when the cell dries out (e.g. at low tide) is ignored when calculating the average.
Figure 11.24 - Figure 11.26 show the peak sedimentation depth during the dredging of the
lower and upper channel sections and on final completion of dredging operations. It will be
seen from these diagrams that sediment is temporarily deposited in a small number of
sheltered areas, mainly along the sides of the channel and along the north shore of the
harbour area, during dredging. Away from these sites the deposition depth is low. It should
be noted that these peak values are typically of a short duration and tend to occur during the
turn of the tide. The material may then be re-suspended as the tidal currents pick up during
the next tidal cycle. If unacceptable localised deposits remain at the end of the dredging
process, these may be cleaned up and reinstated after dredging operations are completed.
11-31
Coastal Processes
Figure 11.24 Peak sediment deposition depths during dredging of lower channel
Figure 11.25 Peak sediment deposition depths during dredging of upper channel
11-32
Coastal Processes
The pattern of residual sediment deposition following the completion of the dredging is
shown in Figure 11.26. It will be seen that significant deposition only occurs in a small
number of sheltered areas along the coastline, particularly in the lee of the training wall and
along small parts of the north shoreline.
Figure 11.26 Sediment deposition depths on completion of all dredging operations
The maximum peak sedimentation during dredging in the affected areas is between 20 and
70mm (Figure 11.24 and Figure 11.25). As described above, much of this deposition is
temporary; occurring only for a very short period of time during slack tide and much of the
material will be re-suspended when current speeds pick up during the following tide.
This resuspension will significantly decrease the final residual amount of deposited sediment
(Figure 11.26), which is therefore lower than the “during dredging” peak values within these
localised areas.
The maximum deposition depth of dredged sediments in Sligo Harbour on completion of
dredging is less than 1mm in the majority of the harbour area. The deposition exceeds
25mm only in a small number of very localised sites, which are mainly around the training
wall and northern shore of the harbour. Outside of this area, two very small sites (less than
300m²) will experience final sediment deposition depths in excess of 25mm adjacent to
Coney Island and at the southern shore of Cummeen Strand.
The combined area of the intertidal sites where deposition depths in excess of 25mm will
occur is 3.5ha. This represents 0.07% of the overall SAC area (c.4854ha).
Overall the amount of sediment deposition in the harbour area on completion of dredging is
considered to be insignificant.
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Coastal Processes
11.2.4 Impacts of Dredging on Sensitive Habitats
During the intertidal/subtidal and birds baseline studies, three areas which have the potential
to be vulnerable to adverse impacts of the dredging activities were identified.
These areas are outlined on Figure 11.27, which also shows the mean suspended sediment
concentration in lower 0.5m of water column during dredging of the lower section of the
channel.
Area 1: The area surrounding Cartron Marsh and Standalone Point, where dredging activity
has the potential to cause impacts on important bird feeding areas. The mean suspended
sediment concentration at this location arising from the dredging operations in the lower part
of the channel is shown in more detail on Figure 11.28 and the upper part of the channel
inFigure 11.32.
Area 2: an environmentally important habitat of seagrass (Zostera) which may be vulnerable
to smothering caused by the dredging. The mean suspended sediment concentration at this
location arising from the dredging operations in the lower part of the channel for this area are
shown in detail on Figure 11.29 and for operations in the upper channel in Figure 11.33.
Area 3: encompassing the main area of commercial and natural shellfish beds, including the
large mussel bank in the centre of the harbour.
The mean suspended sediment
concentration at this location arising from the dredging operations in the lower part of the
channel is shown in more detail in Figure 11.30 and for operations in the upper channel in
Figure 11.34.
In all cases the suspended sediment concentration within the bottom 0.5m of the water
column has been plotted as it is changes to this part of the water column that will have
greatest impacts on the shellfish and intertidal/subtidal bird prey and foraging species which
are present within the harbour.
Figure 11.27: Location of potentially vulnerable areas
11-34
Coastal Processes
Mean suspended sediment concentration in lower 0.5m of water column during
dredging of the lower section of the channel
Figure 11.28: Lower channel dredging - mean suspended sediment concentration in
Area 1 – Cartron/Standalone Point
seagrass habitat in southern part of Cummeen Strand
11-35
Coastal Processes
commercial shellfish farm
The average level of suspended sediment in the bottom 0.5m of the water column during the
dredging operations of the upper section of the channel is shown in Figure 11.31 and in more
detail on Figure 11.32 - Figure 11.34.
Figure 11.31: Mean suspended sediment concentration in lower 0.5m of water column
during dredging of the upper section of the channel
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Coastal Processes
Figure 11.32: Upper channel dredging - mean suspended sediment concentration in
Area 1 –Cartron Marsh/Standalone Point
Figure 11.33: Upper channel dredging - mean suspended sediment concentration in
Area 2 – Seagrass habitat in southern part of Cummeen Strand
11-37
Coastal Processes
Figure 11.34: Upper channel mean suspended sediment concentration in Area 3 –
commercial and natural shellfish beds
The concentrations shown in Figure 11.27 - Figure 11.34 are above background values and
are the average over the time when the particular part of the area is wet during the period of
time that particular section of the channel is being dredged.
Overall the impact of the dredging is expected to be relatively small, as both the deposition
depths and the increase in the level of the suspended sediment concentrations in the greater
part of the harbour area are not particularly significant.
In accordance with the monitoring requirements of Council Directive 79/923/EEC, on the
quality required of shellfish waters, and Council Directive 91/492/EEC, which sets down the
health conditions for the production and placing on the market of live bivalve molluscs, the
Marine Institute collect water and shellfish samples from major shellfish growing areas at
regular intervals and analyses them for physicochemical parameters, trace metal levels and
chlorinated hydrocarbon concentrations. Sampling results were obtained from the Marine
Institute for the shellfish beds within Sligo Harbour for use as a baseline indicator of
suspended sediments.
Table 11.4 below shows suspended sediment concentration values measured in 2009 and
2010 at the same sample location.
11-38
Table 11.4: Water Quality Measurements in Sligo Harbour
by Probe
Lab Analysis
Date
(yymmdd)
Fixed Lat
Fixed
Long
Sample
Depth (m)
DOXY
(%)
PH (sc)
PSAL
(PSU)
TEMP
(degC)
TURB
(%)
CPHL
(ug/l)
AG
(ug/l)
AS
(ug/l)
CD
(ug/l)
CR
(ug/l)
CU
(ug/l)
NI
(ug/l)
PB
(ug/l)
ZN
(ug/l)
SUSP
(mg/l)
COLOR
(sc)
091203
54.2893
-8.5238
0.5
99
8
16.19
8.2
54.2893
-8.5238
0.5
96.3
8.11
26.5
7.79
54.2893
-8.5238
0.5
109
8.23
13.03
7.05
-8.5238
0.5
108
8.45
23.7
7.57
-8.5238
0.5
103
8.32
31.69
9.7
100414
54.2893
-8.5238
0.5
135
8.48
16.65
13.1
-8.5238
0.5
124
8.31
31.85
13.7
6.6
54.2893
-8.5238
0.5
140
8.68
28.12
18.1
100713
54.2893
-8.5238
0.5
130
8.42
32.22
17.7
Ͳ
Ͳ
Ͳ
Ͳ
100823
54.2893
-8.5238
0.5
102
8.34
28.46
17
72
7.9
100920
54.2893
-8.5238
0.5
143
8.8
25.32
16.4
101021
54.2893
-8.5238
0.5
114
8.11
30.11
13.2
Ͳ
Ͳ
Ͳ
Ͳ
110613
54.2893
-8.5238
0.5
110
8.27
28.74
18.9
8
<4
110711
54.2893
-8.5238
0.5
131
8.15
24.5
18.8
<2
30.2
111214
54.2893
-8.5238
0.16
108
7.97
25.58
5.3
22.9
136
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
<2
100623
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
54.2893
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
100517
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
13.6
54.2893
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
12
100323
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
54.2893
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
100216
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
18.6
100120
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
25.6
091216
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
Ͳ
111214
54.2893
-8.5238
0.5
-
-
-
-
-
-
<1
<1
<0.04
<0.5
0.7
0.47
0.19
2.88
-
-
120423
54.2893
-8.5238
0.5
-
-
-
-
-
-
-
-
-
-
-
-
-
-
<5
11.8
120423
54.2893
-8.5238
1.72
105
7.99
30.17
11.2
-
0.49
-
-
-
-
-
-
-
-
-
-
120521
54.2893
-8.5238
1.35
122
8.22
30.76
16.74
9.7
5.83
-
-
-
-
-
-
-
-
-
-
Source: Marine Institute Data Request
Coastal Processes
Figure 11.35 shows the locations of 4 model points which have been chosen as they
represent potentially vulnerable areas. These stations are also replicated as suggested
monitoring points Mon-1 to Mon-4. Month-long time series of the suspended sediment
concentration at these stations have been extracted from the model and are presented in in
Figure 11.36 - Figure 11.39. Point 3 (Mon-3) marked on this figure represents the location of
the measured baseline values shown in Table 11.4.
Figure 11.35: Mean suspended sediment concentration in bottom 0.5m at location of 4
points in potential vulnerable areas
It can be seen that measured values vary widely depending on the date when the
measurements were taken (from <2 to 72 mg/l). The sediments disturbed by the dredging
process in the navigation channel will cause temporary increases in suspended sediment
concentration within Sligo Harbour during dredging. Figure 11.36 to Figure 11.39 shows a
time series of the modelled peak suspended sediment concentrations spanning a typical
month at each of the four “vulnerable area” points.
Figure 11.36: Time series showing Suspended Sediment Concentration in Cartron
Marsh Area during dredging (Point 1)
11-40
Coastal Processes
Figure 11.37: Time series showing Suspended Sediment Concentration in Southern
part of Cummeen Strand during dredging (Point 2)
Figure 11.38:
Time series showing Suspended Sediment Concentration near
commercial shellfish farm during dredging (Point 3)
Figure 11.39:
Time Series showing Suspended Sediment Concentration near
commercial clam farm during dredging (Point 4)
It can be seen that when dredging operations occur during spring tides, the suspended
sediment concentration at each of the four sites shown in Figure 11.36 to Figure 11.39 rises
quickly (around the period of slack water during each tide) but it also quickly returns back to
the background values.
During the spring tide period, the suspended sediment concentrations reach relatively high
peak values during each tide (when compared to the measured background in Table 11.4);
11-41
Coastal Processes
however the actual duration of each “spike” is very short (as dredging only occurs for a short
period each tide). The concentration peaks, or “spikes” at any given point will typically last up
to two hours, but with the highest values lasting for a period of only 15-30 minutes. The
period between peaks (tides), when concentrations return back to near baseline levels, will
be much longer (around 10 hours).
As can be seen on Figure 11.36 to Figure 11.39, during the neap tides suspended sediment
concentration levels at each of the four sites remain at background levels during dredging
operations.
In summary, the modelling shows that significant elevations in suspended sediment within
Sligo Harbour caused by the dredging only occur in the immediate vicinity of where the
dredger is working, within the confines of the navigation channel during periods of spring
tides..
The areas in which sensitive habitats have been identified, at Cartron Marsh, southern
Cummeen Strand and at the various aquaculture sites will experience very short term
increases in suspended sediment concentrations in the lowest 0.5m of the water column,
mainly during slack water at spring tides. As described in Section 6.2.4 of Chapter 6,
“Intertidal and Subtidal Flora and Fauna and Marine Mammals,” as these increases are of
short term duration and are well within the tolerance levels of the sensitive flora and fauna
within the harbour, they are not considered to be significant.
11-42
11.3
Coastal Processes
DUMPSITE PLUME MODELLING
11.3.1 Disposal Site Dispersion
Material from the planned channel dredging in Sligo Harbour is to be dumped at a proposed
location offshore of Donegal Bay. The impact of the dumping operation on sedimentation and
suspended sediment loads in the area was assessed by undertaking a computational
modelling exercise using the MIKE321 NPA particle tracking model.
The dispersion characteristics of the proposed disposal site were assessed by simulating the
disposal of circa 49,300m3 of saturated silty sand over a one month period. With an
approximate specific gravity of 1.41t/m3 for 25% saturated silty sand, this equated to circa
69,600 tonnes of dredge material for disposal at the dumping site. The grading of the
disposal material used in the dumping simulations was in accordance with those used in
dredge modelling and are presented in Table 11.1.
The location of the proposed dumping site is shown in Figure 11.40 as a red square, with the
surrounding blue square indicating the extent of the detailed area used in the sediment
modelling.
Extract from Admiralty Chart 2725 & 2767 © Crown Copyright UKHO. Not for navigational use
Figure 11.40: Extents of sediment dumping hydrodynamic model (blue square) and
proposed dump site location (red square)
Given the distance from the dredging site to the disposal site (approx. 50km) and the time
restriction due to the movement of tides in the area, it was calculated that the dredging would
take 5-6 months. In order to understand the effects of the dumping process one month of
dumping was necessary to be modelled, with the assumption that the disposal will occur
during every low tide, with an average dredging rate of 850m3 per dump cycle. This value is
11-43
Coastal Processes
dependant upon barge capacity which was assumed at 1200 tonnes per barge. The speed
of the barge during the dumping was assumed to be 4mph with 10 minutes being required for
the dumping process. It was assumed that no washout from the barges will occur, and that
the disposal source will be located at the water surface.
11.3.2 Modelling System
For the sediment dispersion simulations RPS used the MIKE321 NPA model which describes
the transport and fate of solutes or suspended matter and uses data from the corresponding
hydrodynamic model to provide information on the general movement of the water body.
Within MIKE 321 NPA the sediment is considered as a series of discrete particles being
advected with the surrounding water body and dispersed as a result of random processes in
a 2-Dimensional or 3-Dimensional regime using the Lagrangian approach. Hence, the
resolution of the sediment plume is not restricted by the grid size of the current field.
The model can be used to determine the fate of suspended or dissolved matter that is
discharged or accidentally spilled in lakes, estuaries, coastal areas or the open sea. The
model can simulate the effects of wind driven currents, including a mechanism for dealing
with the overturning currents at the shoreline. The loss of active material from the water
column through either settling or decay can also be included within the model simulations.
The model can use data from 2-Dimensional depth averaged hydrodynamic flow models; in
such cases the MIKE321 NPA model applies a logarithmic vertical velocity profile to the tidal
current component to provide a more accurate assessment of the displacement of particles
located at different depths in the water column. This facility provides a more realistic
representation of the situation at full scale.
In order to run the Mike 321 NPA model, it was necessary to determine the hydrodynamic
conditions across the model domain by means of a series of Mike 21 flexible mesh and
rectangular mesh models. A one month hydrodynamic model with fluxes was used to
construct the 45m grid model used in the dispersion modelling. Tidal level boundaries for the
model which formed the basis of the hydrodynamic data were extracted from RPS’s flexible
mesh Irish Seas Tidal and Surge model (ISTSM) which provides hydrodynamic information
offshore in the water bodies surrounding Ireland. The extent of this base model covered
much of Ireland’s west coast centred on Donegal Bay and the Atlantic Ocean as shown in
Figure 11.41.
11-44
Coastal Processes
Figure 11.41: Flexible mesh model base model
The sediment modelling was undertaken on a 45m grid rectangular mesh, the domain of
which is shown in Figure 11.42 as a red square on the zoomed extent of the flexible mesh
base model. Figure 11.43 shows the extent of the 45m grid model and its bathymetry. The
extent of the deposition area was given as 1km2 and is depicted by a yellow square.
Analysis of the tidal excursion and residual current was used to determine the necessary
extent of the sediment transport model. Due to the low current velocities at the site, the
extent of the 45m grid NPA model was a 11.25 km square area with the dumping site located
in its centre. The model size was sufficient for the analysis as no material exited the model
domain during the course of the simulations, as can be seen in the result plots in Section
11.3.4.
11-45
Coastal Processes
Figure 11.42: Flexible mesh model – zoomed extents
Figure 11.43: Extent of 45m grid with deposition area marked by yellow square
11.3.3 Ambient Tidal and flow Conditions
In order to determine the influence of the proposed disposal, the plume extent and
sedimentation was established over a simulation period of 1 month from mid September till
mid October 2009 and incorporated both spring and neap tidal ranges. A time series of tidal
elevation over the modelling period is shown for the dump site in Figure 11.44.
11-46
Coastal Processes
Figure 11.44: Tidal elevations at the dump site over simulation period
The peak spring flood and ebb tide flow patterns are shown in Figure 11.45 and Figure 11.46
respectively. The tidal velocities in the extent of the model including the dump site are small
with peak spring tidal velocities of circa 0.16 m/s.
Figure 11.45: Tidal flow around deposition site - Mid flood spring tide
11-47
Coastal Processes
Figure 11.46: Tidal flow around deposition site - Mid ebb spring tide
Dredged spoil deposited on the sea bed at the proposed disposal site may also be subjected
to wave action during gales and storms; this is examined in Section 11.3.5.
11.3.4 Modelling Results
11.3.4.1
Model calibration data
The NPA model was verified using field data collected specifically for this study. Drogue
measurements were carried out to provide information on tidal currents in the surface, middle
water column and bed layer during neap (27 Jan 2011) and spring (17 Feb. 2011) tides. In
addition to the release of drogues, current speed and direction was measured at the site of
each drogue drop location. The series of figures below show current speed and current
direction recorded at these locations in the mid water column depth and current speed and
direction from the model results (shown as a solid line).
It should be noted that the model simulation period was not the same as the monitoring
period and therefore data was compared in terms of tidal range. In order to match the data
from when the measurements were collected with the modelled tides the tidal elevation for
Jan 2011 and Feb 2011 was predicted using harmonic data published by the UK
Hydrographic Office. The predicted tidal ranges were aligned with those in the model results
on 6 Oct 2009 for the spring tide (Figure 11.47 and Figure 11.48) and for the neap tide on 11
Oct 2009 (Figure 11.49 and Figure 11.50).
11-48
Coastal Processes
Figure 11.47: Measured and modelled current speed – site of drogue release 1 spring
Tide
Figure 11.48: Measured and modelled current direction – site of drogue release 2
spring tide
Values for current direction measured during the spring tide are slightly higher than those
modelled but current direction correlates well with the measured values. Current speed
measured during neap tide (Figure 11.49) show widely scattered values. As it is very
unlikely that the current speed changed its magnitude so rapidly between successive
readings and that the current changed direction every 10 minutes with such a magnitude, it
has to be concluded that due to low tidal range during neap tide there is significant amount of
noise in the measurement data.
11-49
Coastal Processes
Figure 11.49: Measured and modelled current speed – site of drogue release 1 neap
tide
Figure 11.50: Measured and modelled current speed – site of drogue release 2 neap
tide
The following figures present in detail a sample of the particle tracks for different tidal
conditions and drogue measurements. In each case, the particle tracking facility within the
MIKE modelling software was used to describe the route of a particle when released at an
equivalent location and tidal state as each drogue released in the field measurements. The
hydrodynamic model data was used to determine the course of the particle under advection
for the same duration as the drogue release.
Figure 11.51 shows a drogue drop during neap tide at high water. Figure 11.52 shows a
drogue drop during spring tide at low water and Figure 11.53 shows a mid flood drogue drop
along with Figure 11.54 a mid ebb drop. The white line on the figures indicates the modelled
track of a single particle in the middle of the water column whereas the coloured points
indicate the measured drogue position at a particular time in approximately 5 minute
intervals.
11-50
Coastal Processes
Figure 11.51: Drogue track at neap tide in mid layer (drop at high water) and particle
track from the model
Figure 11.52: Drogue track at Spring tide - mid layer (drop at low water) and particle
track from the model
.
11-51
Coastal Processes
Figure 11.53: Drogue track at mid layer (mid flood drogue drop) and particle track
from the model
Figure 11.54: Drogue track at mid layer (mid ebb drogue drop) and particle track from
the model
As can be seen on these figures, the modelling results largely correspond to the measured
data in terms of direction and the distance the particles will travel. It should be noted that the
11-52
Coastal Processes
modelled data is driven by tidal currents alone and will not replicate meteorological
conditions which may have been present at the time of the field studies.
11.3.4.2
Sedimentation and concentration modelling
Sediment sampling at the proposed dredging site has indicated that the sediment comprises
sand and silt. Table 11.11.5 shows grain distribution used in the modelling. This is in
accordance with the modelling of the dredging process in Sligo Harbour channel.
Table 11.11.5: Grain diameter occurrence used in modelling
Grain Diameter [mm]
% Occurrence
0.375
6
0.187
62
0.090
20
0.050
7
0.030
5
Deposition of the dredged spoil at the disposal site was simulated by modelling the
dispersion of the spoil as the dredger carried out the dumping process at the site. The
dredger was assumed to traverse over the disposal site as it released each load over a 10
minute period. This occurred once in every circa 12 hours at a distance of 1m below the sea
surface. Due to operational constraints the dumping took place during low tide and the
simulations were run for a full month. Figure 11.55 below shows a plot of the course of a
particle released in the centre of disposal area over the modelled 1 month period. This
would represent the path of the finer material which is more easily re-suspended and it can
be seen that the material will be gradually transported towards the open sea due to the
residual current.
11-53
Coastal Processes
Figure 11.55: Track of suspended sediment over a month of tides
The maximum plume concentration in the water column during the modelled period is shown
in Figure 11.56. These values are the maximum that occur at any time during the dredging
operation even if it is only for a very short period of time and would therefore not necessarily
occur concurrently. The mean value of the suspended sediment concentration in the water
column over the one month period is shown in Figure 11.57. It can be seen from these
diagrams that the suspended sediment values beyond the immediate vicinity of the dumping
operation are minimal. Figure 11.58 illustrates total sedimentation depth (in mm) after
deposition of 250,000m3 dredged material, and was calculated by scaling the deposition
observed during the 1 month simulation period. It indicates that the majority of the material
will be deposited and remain within 2km on the dumping site with only a small amount of
material being transported further offshore by the residual current.
11-54
Coastal Processes
Figure 11.56: Maximum suspended sediment concentration in the water column
Figure 11.57: Mean suspended sediment concentration in the water column
11-55
Coastal Processes
Figure 11.58: Final Deposition of sediment at the end of dredging operations
11.3.5 Wave induced Sediment Transport
In addition to the sediment transport induced by tidal currents, wave induced sediment
transport was also investigated. The sediment which is proposed for deposition at the site is
mainly fine sand and silt; it is therefore relatively easily re-suspended. However the water
depth at the site is of the order of 90m which will reduce the impact of waves. Analysis of the
nature of the material suggests that in order for significant re-suspension to occur current
speeds in excess of 0.05m/s would be required, although the very fine silt fraction would
require lower velocities.
Using the horizontal velocity equation it was determined that longer period swell waves
would be required in order to penetrate to the deposited material on the bed; in excess of 10
seconds mean period and with a significant wave-height greater than 3m. The wave climate
within Donegal Bay, for a location close to the proposed dumping site, was examined using a
9 year dataset supplied by the European Centre for Medium-range Weather Forecasting.
Statistical analysis showed that the conditions required to mobilised material at the seabed
occurred for less than 15% of the time. Figure 11.59 shows the wave rose for this period
while Figure 11.60 shows the corresponding plot for the mean wave period.
11-56
Coastal Processes
Figure 11.59: Significant wave height Donegal Bay
Figure 11.60: Mean wave period Donegal Bay
During these events the material at the bed may be re-suspended however any subsequent
transport will take place by advection on tidal currents. In the area of the dump site the tidal
currents are weak and the material would not be transported significant distance before the
current speeds reduce at slack water and the material is deposited, or if it remains in
suspension it will be carried back to the site on the returning tide. This has already been
demonstrated in Figure 11.55.
11.3.6 Dumping at Sea Impacts Summary & Conclusions
The final settlement model (Figure 11.58) shows that most of the dumped sediment will settle
on the seabed close to the dump site. Some of the material will migrate towards the east
under the influence of tidal action, but all particles will settle within 5.5km of the dump site.
11-57
Coastal Processes
An area extending across approximately 2km to the east and south of the dumpsite will
experience deposition in excess of 20mm. Within this, an area measuring approximately
0.5km² will experience deposition depths in excess of 130mm.
It can be seen from the suspended sediment and deposition diagrams that the proposed
dredging will not have a significant impact on bed sediments or water quality in a waters
beyond the immediate vicinity of the dumping site. No mitigation is possible to reduce the
extent of the affected areas, however Section 6.3.4.1 of Chapter 6, “Intertidal and Subtidal
Flora and Fauna and Marine Mammals” describes the significance of this impact, and
concludes that as the impacts are temporary in nature with recolonisation occurring within a
year, there is no significant impact arising from the deposition of the dumped sediments.
Sediment transport due to wave action is likely to be limited at the site due to the 90m water
depth. Any material which is driven into suspension during large swell events will not be
transported far from the site due to the weak tidal currents.
11-58
Cultural Heritage
12.0 CULTURAL HERITAGE
12.1
Introduction
The Archaeological Diving Company Ltd (ADCO) was appointed by RPS Consulting
Engineers on behalf of Sligo County Council to undertake an archaeological and architectural
heritage assessment in advance of dredging works proposed within Sligo Harbour and its
approach channel.
The dredging will occur along the existing approach channel from the quays in Sligo Port to
Oyster Island (Figure 12.1). The dredged material will be disposed of at an approved marine
disposal area located some 52 km (28 nautical miles) northwest of Bungar Bank, west of
Donegal Bay and southwest of Malin More Head, Co. Donegal and north of Downpatrick
Head, Co. Mayo (Figure 12.2).
The study area comprises the works areas, while the architectural heritage assessment is
required to include the immediate vicinity of Sligo Harbour and the wider locality where there
might be any significant impact. The dredge areas are located within a Natural Heritage Area
(NHA), a Special Area of Conservation (SAC) and a Special Protection Area (SPA).
The archaeological and architectural assessment is based on a desktop review of existing
archival and published information. The architectural heritage assessment included a site
inspection of the Sligo Port area and immediate vicinity and is reported as Appendix 7C of
the Report. A marine geophysical survey of the dredge areas and the disposal area was
carried out under licence from the Department of the Environment, Heritage and Local
Government (DoEHLG)1, licence 11D010, and is reported in Appendix 7D of the
Environmental Report. The primary geophysical survey data was reviewed and interpreted
by a maritime archaeologist and is absorbed within the present report.
The following Chapter addresses the known and potential archaeological and architectural
heritage environment; assesses the actual and proposed impacts on that environment from
the works programme; and makes recommendations to resolve any further archaeological
requirements prior to the works programme commencing and during dredging operations.
A full description of the dredging works is presented in Chapter 4, “Project Description”
12.2
ASSESSMENT METHODOLOGY
A desk study of cartographic and archival information was conducted as a preliminary stage
of archaeological assessment for the project.
x
Topographical files in the National Museum of Ireland;
x
Register of Monuments and Places in the Department of Arts, Heritage and the
Gaeltacht (DoA,H&G);
1
Heritage functions were transferred from the Department of Environment, Heritage and Local
Government (which has since been re-named to the Department of Environment, Community and
Local Government) to the Department of Arts, Heritage and the Gaeltacht with effect from 1 May 2011
12-1
x
x
x
x
x
x
x
Cultural Heritage
National Inventory of Architectural Heritage;
Ordnance Survey mapping for the area since the First Edition six-inch series in 1838;
Admiralty Charts;
Other historic mapping;
Inventory of Historic Shipwrecks and the Ports and Harbours record at the DoA,H&G
the record of licensed archaeological work;
relevant published sources were reviewed.
The following legislation, standards and guidelines were considered and consulted for the
purposes of this evaluation:
x
x
x
x
x
x
x
x
x
x
x
x
x
Advice Notes on Current Practice (in preparation of Environmental Impact Statements),
2003, EPA;
Architectural Heritage (National Inventory) and Historic Monuments (Miscellaneous
Provisions) Act, 2000 and the Local Government (Planning and Development) Act 2000;
Frameworks and Principles for the Protection of the Archaeological Heritage, 1999,
(formerly) Department of Arts, Heritage, Gaeltacht and Islands;
Guidelines for the Assessment of Archaeological Heritage Impacts of National Road
Schemes, NRA;
Guidelines on the information to be contained in Environmental Impact Statements,
2002, EPA;
Heritage Act, 1995;
National Monuments Acts, 1930-2004;
Planning and Development (Strategic Infrastructure) Bill, 2006;
Strategic Environmental Assessment (SEA) Pack, 2010 EPA;
In the absence of a specific Code of Practice between the Marine Industry and the
Minister of the Environment, Heritage and Local Government, the following Codes of
Practice that exist between industry and the Minister were consulted: Bord Gáis Éireann
(2002); .Coillte (no date); EirGrid (2009); ESB Networks (2009), Irish Concrete
Federation (2009), National Roads Authority (no date), Railway Procurement Agency
(2007).
The following county and local development plans were considered and consulted for
the purposes of this evaluation:
County Sligo Heritage Plan 2007-2011.
County Donegal Development Plan 2006-2012.
On-site marine geophysical survey and architectural fieldwork has been carried out as part of
the present report.
12.2.1 Limitations
No limitations were encountered during the desk study.
12.2.2 Classification of Impacts/Effects
Impact/effect categories will typically have regard to those set out in the ‘Guidelines on the
information to be contained in Environmental Impact Statements’, 2002, EPA; ‘Advice notes
on Current Practice (in preparation of Environmental Impact Statements), 2003, EPA;
12-2
Cultural Heritage
‘Strategic Environmental Assessment (SEA), 2010’; and ‘Guidelines for the Assessment of
Archaeological Heritage Impacts of National Road Schemes’, no date, National Roads
Authority. Impacts/effects are generally categorised as either being a direct impact, an
indirect impact or as having no predicted impact.
12.3
THE RECEIVING ENVIRONMENT
The specific details of individual observations are set out in Appendix 7A. A general overview
of what the sum of these observations implies is presented below, and this is followed with
individual presentations of the relevant source material.
12.3.1 Overview
The presence of Maeve’s Cairn southwest of Sligo town bears witness to the importance of
Sligo Harbour as a natural inlet and landing place since early prehistoric times. The cairn
which sits on top of Knocknarea acts as a sentinel overlooking the harbour and the
landscape around and about. It would also have served as a beacon, to draw early settlers
safely in from the Atlantic to the haven of the harbour. The development area for the present
project occurs beyond the limits of what was subsequently to become the town of Sligo, and
there is a small collection of artefacts and small field monuments, such as burials known as
barrows, which reveal the extent of the prehistoric footprint on the headlands around the
harbour. Shell middens are found in some numbers along the shoreline and these sites serve
as the real testimony to active marine exploitation. Although none of the midden sites have
been subject to scientific dating, it is clear from their partially buried nature that these most
reasonably belong to the preshistoric period. Oysters, winkles and periwinkles were caught
and processed on the shore, the users then throwing the shells into large heaps or middens,
where they were discarded.
Later settlement sites of enclosures and ringforts are positioned at a slight remove from the
shoreline. They reveal the imprint of settlement in the period after saints Palladius and
Patrick worked in Ireland in the fifth century to bring Christianity and to usher in a social
transformation that was in keeping with change across Europe. Society in the early medieval
period remained rural, and would have focused on crop husbandry and livestock, while the
proximity to the sea that we see around the harbour would have dictated a continued
relationship with fishing and coastal trade.
It is in the later medieval period that Sligo town emerges. A bridge existed in 1188 across the
Garvogue river, establishing the importance attached to the settlement’s location on the main
road north from Galway to Donegal. The word Sligo, Irish Sligeach meaing ‘shelly place’,
tempts one to see the continued connection with shell-fishing. A description of the island at
the mouth of the Garavogue or Sligo River in the year 1599 mentions that, ‘at every tide they
may gather great store of oysters, cockles and mussels, all of which will be a great help with
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her Majesty's stores’.2 Certainly from the seventeenth century, the town relied heavily on
fishing and oyster in particular.
Sligo is also linked intrinsically to the O’Conors during the later middle ages, and the
settlement’s strategic importance, both as a safe haven from the Atlantic and as a
communications hub was endorsed by the construction of a fortification, the arrival of the
Domincans in1253, and also town defences. Sligo was pivotal to powers seeking to control
Ulster. It presented the first significant harbour on the northwest coast south of Donegal,
while routeways through the hills inland gave access across the Curlews to Boyle in north
Roscommon, after which there were ample connections south and east to Roscommon town,
Athlone and ultimately Dublin. These routes on land and sea were to be of critical importance
to the Tudor administration in their attempts to ‘plant’ Connacht and subdue Ulster in the late
1500s, and conversely Sligo was a prize to be kept by the Irish. The presence of Ballincar
castle on the north shore of the harbour reveals something of the later medieval ownership.
The star-shaped fort on Coney Island at the mouth of the harbour is a more telling statement
of the manner in which the town and its settlement were protected in the seventeenth
century.
With relative peace and prosperity in the period after Cromwell, Sligo was able to realize its
trading potential in terms of Atlantic traffic and also fishing, particularly with oysters and
mussels. Navigation into the harbour required the construction of various markers and buoys.
The early nineteenth-century construction on Perch Rock, the Metal Man (1822), is an
example of Victorian prosperity and confidence, with this popular figure pointing out the
direction of safe passage across the straits into the harbour. The presence of private weirs
and mills were increasingly seen as problematic to the growth of the town’s trade. A series of
reports focus on such issues and ultimately reveal the frustration that the compact medieval
town experienced as it tried to grow beyond its boundaries. The town remained focused and
congested to the south of the current works area. By 1884, however, deep water berths had
been constructed, while a railway established in 1898 connected Sligo to Ireland more
generally. Further work in the 1930s looked at the old timber jetties in the deep water quay
area, and replaced them with a 245-feet long concrete wharf. Additional growth occurred in
1936. As will be seen below, the geophysical survey conducted for the present project
reveals crisp images of the navigation aid perches that line the approach channel. Built on
mounds of stone, the perches are particularly apparent across the north side of the Middle
Bank sand mass, where they and the training wall that was built after the perches, serve to
constrain the bank from reforming. The dredging project that is currently proposed is the
most recent in Sligo’s long history of port development, balancing the natural dynamic of a
tidal haven with the need to maintain access from the sea.
2
Quoted from A. J. Went, ‘Historical notes on the oyster fisheries of Ireland’, Proceedings of the Royal
Irish Academy 62 (1961-63): 195-223, p. 213.
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12.3.2 Placenames
Archaeological information is generally identified and located with reference to townland
names, and consequently the townland is the principal basis for registration in both the
archives of the National Museum of Ireland and in the Department of Arts, Heritage and the
Gaeltacht. It is the case that sometimes more local names are cited as well, particularly with
reference to maritime information, which can derive from location at sea, removed from
actual townlands on the shore. The townlands and placenames/topographic features
considered for the present study are indicated in Table 12.1.
Table 12.1
Townlands and placenames identified within the Sligo study area.
Maps
Townland
Other placename
Ordnance Survey
6-inch series, Sligo
Sheet 14
Ballincar
Cartron
Cartron (Honoria Duff)
Cummeen
Finiskilin
Inishmulclohy or Coneyisland
Knappagh More
Rathedmond
Rathquarter
Rinn
Shannon Eighter
Sligo
Tully
Cartron Marsh
Cummeen Strand
Doonanpatrick
Dorrines Strand
Garavogue River
Inner Harbour
Middle Bank
Oyster bed
Seal Bank
Srunamoyle
Standalone Point
OS 6-inch series,
Sligo Sheet 8
Ballyweelin
Rosses Lower
Rosses Upper
Bomore Race Course
Deadman’s Point
Drumcliff Bay
Rosses Point
The Metal man
OS 6-inch series,
Sligo Sheet 7
Ardtermon
Cloghcor
Raghly
Ardtermon Strand
Bird’s Rock
Black rock
Sea Charts
Ardboline
Altconeen
Ballysadare Bay
Black Rock
Blind Rock
Bomore Strand/Point
Bungar Bank
Cartron Marsh
Cluckhorn
Drumcliff Bar
Drumcliff Spit
Pool Doy
Raghly Ledge
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Townland
Other placename
Sligo Bay
Sligo Harbour
12.3.3 Topographic files, National Museum of Ireland
The National Museum of Ireland’s Topographical Files is the national archive of all known
objects reported to the National Museum. These files relate primarily to artefacts but also
include references to monuments and contain a unique archive of records of previous
archaeological excavations. The Museum's files present an accurate catalogue of objects
reported to that institution from 1928. There is a computerised database of finds from the
1980s onwards. The find-spots of artefacts can be an important indication of the
archaeological potential of the related or surrounding area.
There are seven series of entries noted in the records of the National Museum of Ireland and
these are listed in Appendix 7A. An old find provenanced as being ‘from Sligo’ represents an
exotic figurine whose origins are not clear but may ultimately suggest an Iron Age piece from
Iberia. A small amount of artefacts have been deposited in the Museum from the study area
more recently, including two copper axes from Sligo (1959:65, 92), a chert flake (1934:4267)
and three stones flakes (1936:1577-79) from Rosses Lower. These do not amount to
observations of great significance but they do attest to evidence for prehistoric activity in the
wider area. Small collections of material from Raghly suggest the presence of more
substantial archaeological material, ranging from prehistoric times into the early medieval
period (1905:5-9, 1934:4182-4225). There are no apparent records in the Museum for
artefacts or features observed from within the proposed dredging or disposal areas.
12.3.4 Record of Monuments and Places3
The Record of Monuments & Places (RMP) is a list of archaeological sites known to the
National Monuments Service with accompanying RMP Maps, based on OS 6-inch Sheets,
which indicate the location of each recorded site. The RMP list is based on the Sites and
Monuments Record (SMR) files housed in the National Monuments Services offices. The
SMR comprises lists with accompanying maps and files of all known or possible
archaeological sites and monuments, predominately pre-1700 AD in date, for all counties.
These lists were, in many cases, initially based on cartographic, documentary and aerial
photographic sources. The SMR (as revised in the light of available fieldwork) forms the
basis of the statutory RMP. The record is updated on a constant basis and focuses on
monuments that predate 1700 AD. Buildings belonging to the seventeenth-century and later
are not well represented in the archive, although they are considered as archaeological sites
today.
A large number of archaeological sites exist in the landscape around Sligo, ranging in date
from early prehistory to more recent times (Figure 12.3). For the purposes of the present
3
The RMP is maintained by the National Monument Section, Department of Arts, Heritage and the
Gaeltacht.
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study, those monuments that lie within c. 500m of the proposed dredging operations were
considered as they are most likely to reflect the immediate maritime/foreshore context. In
addition, sites on Oyster Island and Coney Island were included for the same reason,
although they are at a further remove from the development areas. The selection presents a
total of twenty-one known monuments, as listed and described in Appendix 7A. None of the
sites occur within the areas proposed for dredging operations.
Sligo is known for its attention to the fishing industry during the nineteenth and early
twentieth centuries, where particular emphasis was given to oyster fishing. The tradition
continues into the present day with aquaculture. It is therefore of little surprise that there are
five known shell midden sites observed on the foreshore around the harbour area (SL008099 and -101, and SL014-13, -56, -63). They are found widely distributed on Coney Island,
Oyster Island, Ballincar, Finisklin and Cartron respectively, as shallow exposures of
concentrated heaps of shells that have become buried over time by the natural accumulation
of soils and sands. These sites do not refer to the recent exploitation of shell fish but rather to
a much older exploitation that may extend back into prehistory, and reveal the presence of
fishing-related activities along the foreshore, where presumably the early fishermen
processed their harvest of shells from netting activity and possibly from work on boats and
small craft. An intertidal survey of the harbour area conducted in 2010 identified a further
midden site southwest of the present study area, on Doonan Patrick Island. The work also
identified a probable fishtrap on the marshy ground in Cartron townland.4
Of the remaining known archaeological sites, the most numerous is a set of three enclosures
and four ringforts, which are located overlooking the northern shoreline of the study area.
Enclosures refer to circular earthworks whose remains are quite denuded but may originally
have been more clearly defined as ringforts. These sites served as the household residences
for the freemen of society in the early medieval period, and the more elaborate types, which
are encircled by more than one bank and ditch, are believed to have been associated with
those of higher status. They are a common site type across Ireland and reveal the presence
of a well settled and populated rural landscape in the period c. 500-1000 AD, which exploited
the marine environment just as it cultivated the soil and raised livestock. There are no early
church sites within the immediate study area, but the well known island site of Inishmurray
lies some kilometres to the north.
The only vestiges within the study area of the bustling activity associated with the late
sixteenth century is a small star-shaped earthen fort on Coney Island (SL014-002), and a
slightly later fortified house and associated wider settlement at Ballincar (SL014-005). The
location of both sites close to the navigation channel reflect the obvious interest in using the
resources that come in from the sea and in controlling them. The location of the star-shaped
fort on Coney Island is positioned on its NE extremity, looking into the harbour rather than
defending its external approaches. A slipway has been identified that may have been
4
Auriel Robinson, ‘Discovering the maritime archaeological heritage of Sligo Harbour and environs’,
unpublished report submitted to the Heritage Council in 2010, grant reference R00697, pp 245, 38.
Further reference is made in Appendix 1 of the present report.
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associated with the fort.5 This would have permitted the occupants to have quick access to
the deep water of Srunamoyle. Without doubt the fort would have served as part of the
larger defences of the town in the seventeenth century, where most attention was given to
the Green Fort, positioned to the north of the town on high ground overlooking the bridge.6
12.3.5 Intertidal Survey
An intertidal archaeological study of Sligo Harbour and its environs was completed in 2010,
and the results of that useful work have been made available and absorbed in the present
study (Table A7.3 in Appendix 7A).7 As noted above, Robinson has added a series of
observations that provide additional sites, including a prehistoric midden on Doonan Patrick
Island, a probable fish-trap in Cartron, and the early slipway on Coney Island. The study has
also presented a large number of mainly nineteenth-century and early twentieth-century
features that comprise of a series of formal bathing places, small jetties, and a number of
abandoned boats and trawlers (Figure 12.4). None of the sites or features occur within the
areas proposed for dredging operations.
12.3.6 National Inventory of Architectural Heritage
The National Inventory of Architectural Heritage (NIAH) is a county by county database that
identifies, records and evaluates the post-1700 architectural heritage of Ireland, uniformly
and consistently as an aid to the protection and conservation of the nation’s built heritage.
The NIAH surveys provide the basis for the recommendations of the Minister for the
Environment, Heritage and Local Government to the planning authorities for the inclusion of
particular structures in their Record of Protected Structures (RPS).
The series of structures recorded for the present project are listed in Table A7.4 in Appendix
7 and are also summarised in Figure 12.4. It amounts to a small number of largely
nineteenth- and early twentieth-century structures, most of which are domestic residences,
but one is a warehouse site on the Sligo quays (Batchelors/Davitt’s warehouse), and all are
at a remove from the development areas. The baseline information serves to further inform
the more recent history and development of Sligo town and the extension of settlement along
the coast, but none of this material will be impacted in any way by the proposed dredging
works.
5
Robinson, ‘Discovering the maritime archaeological heritage of Sligo Harbour’, p. 31.
The Coney Island fort does not appear to have received scholarly attention, but the Green Fort is
mentioned in Paul Kerrigan, Castles and fortifications in Ireland 1485-1945 (Collins Press, Cork 1975),
pp 98, 102, 122-3.
7
Robinson, ‘Discovering the maritime archaeological heritage of Sligo Harbour’.
6
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12.3.7 Cartographic Sources
12.3.7.1
Sligo
Sea charts and Admiralty charts showing Sligo Harbour and the wider area of the Bay reveal
useful information concerning the depths and presence of navigation hazards, as well as
naming places and locations of topographic interest, but they show little that is of
archaeological interest. A series of charts was examined, including Chart 2767 Sligo and
Killalla Bays, 1852-4, reprinted 1957, and Chart 2852 Approaches to Sligo and Sligo
Harbour, 1998. One chart of Sligo and Ballysadare Harbours dated 1852 and corrected in
1859 does show the location of the wreck Lord Drogheda’s yacht, which was lost in 1859
while navigating into Sligo. The yacht ran aground on shallows to the west of Coney Island.
The shallows had been marked by a buoy but that had fallen into disrepair and had not been
in place for two years, to the detriment of the luckless yacht (Figure 12.5).
The Ordnance Survey First edition 6-inch series made in 1838 in turn reveals little
information about the active water bodies within the harbour but does record a series of
elements along the foreshore that reveal the landscape prior to the development of the quay
walls in the 1840s (Figure 12.6). A series of marker buoys and posts define the natural
course of the Garavogue river as it makes its way seawards, meandering through the mud
flats of the inner harbour. This is in contrast to the defined linear navigation channel which is
maintained today and is the subject of the present study, running northwest before
enhancing the relatively straight channel alongside Ballincar and Ballyweelin townlands. The
new dredging works will maintain the approach channel that has been in use for some
considerable time, stopping short of Oyster Island to its East. The 1838 maps record the
foreshore in considerable detail. Apart from the navigation aids there is an absence of
obvious features such as fish traps and quays/jetties that attest to the active use of this area.
Yet, as Robinson’s intertidal survey suggests below, there are features of archaeological
interest that predate the 1800s and were not noted on the early maps. These include a fishtrap and/or fording point across tidal mudflats in Shannon Eighter townland, some 350m from
the navigation channel, and a series of shell middens that complement the existing evidence
of middens recorded in the SMR, attesting to the widespread use of the Bay over time to
exploit oysters as well as periwinkle and other such shellfish.
12.3.7.2
Marine disposal area
Sea charts examined for the marine disposal area included Chart 3471, Irlande Côte NordOuest 1956, and US Chart 4722, Downpatrick Head to Horn Head, 3rd edition 1948. In no
instance were any features observed that indicate the presence of shipwreck material within
the disposal area.
12.3.8 Shipwreck Inventory
The Shipwreck Inventory in the Department of Arts, Heritage and the Gaeltacht’s archive is a
list of recorded instances of wrecking since 1750. The details provided describe the type of
vessel, the journey it foundered on, and information on the ultimate plight of the vessel and
its crew, where possible. In describing the wrecking event, the records will locate the incident
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in relation to the nearest headland or other topographic marker where known. This is not
however a record of where the wreckage lies, since the historic records generally only deal
with the vessel before it sank. Such finer details emerge from other sources, such as
fishermens’ records of snag points and diver records of sites located underwater. These are
included in the Inventory wherever possible but it is true to say that most entries lack this
final level of data. Finally, it should be pointed out that while the Inventory provides a record
of wrecking incidents since 1750, it does not claim to be a comprehensive record for earlier
events, and therefore the medieval and prehistoric periods are not represented in the
archive.
12.3.8.1
Sligo
Thirty-five shipwreck incidents are listed in Table A7.6 of Appendix 7A for the Sligo Harbour
and Bay area. A further twenty-four events are noted in the Historic Shipwreck Inventory but
the information pertaining to their location is quite vague, registered broadly to ‘Sligo’, and
nine more wrecking events are registered to Sligo Bay. Overall, the number of wrecking
events is not significantly large when compared with other coastal stretches around Ireland,
even allowing for the relatively short amount of coastline in the county.8 The known
shipwreck location of the 1588 Spanish Armada vessels to the north of the study area on
Streedagh Strand are without doubt the most discussed of the county’s wrecks. Leaving
these aside, the wrecking events considered for the Sligo Harbour area retain a similar
chronological spread to those recorded elsewhere. Nine relate to the eighteenth century. The
earliest recorded wrecking took place in 1757, when the Sarah was sailing to the Virgin
Islands from Liverpool and was driven ashore in Sligo Bay during foul weather and was
damaged considerably. The ship Brothers had almost made port, sailing from New York in
1788 when she struck on Sligo Bar and was lost. Wreckage because of underwater
obstructions led inevitably to the formalization of safe navigation channels, and the figurative
navigation beacon on Perch Rock, known as the Metal Man and cast in 1819, has his hand
pointing to the safe passage for shipping as they enter and leave the harbour. The largest
number of wrecking events belongs however to the nineteenth century, where a total of fortytwo events are recorded. To encounter foul weather and storms at sea continued to prove
very hazardous, but the large numbers also attest to the growth in maritime traffic associated
with the burgeoning economies of the industrial age. This in turn presented the opportunities
to invest in shore-based infrastructures, and it is in the 1830s and ‘40s that we see the
development of the quayside at Sligo and their extension seawards, and also the
improvement to the pier at Raghly.
There are two known instances of wrecking on the Bungar Bank, and both date to 1859. An
Austrian brig, the Naslieduk was carrying a cargo of maize when she wrecked, while Lord
Drogheda’s yacht, the Fancy, ran aground on shallows just off Coney Island where a
navigation buoy had fallen into disrepair. The site of the Fancy is plotted on an 1859 chart
but it is not plotted on current charts. The specific location of the Naslieduk is not known. In
this, the Austrian brig shares much in common with the majority of the recorded
8
The East coast area has considerable numbers of wrecks clustered around the principal coastal
towns; see Karl Brady, Shipwreck inventory of Ireland. Louth, Meath, Dublin and Wicklow (Dublin,
Stationary Office, no date).
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shipwrecking, but eight (including the Fancy) have been accurately positioned (Figure 12.4).
They include the ruined remnants of the two lighters Gartnasheerie and Molbec, which were
in service in the early twentieth century but are now pulled ashore onto the mudflats. The
majority of such known shipwreck site locations refer to twentieth-century wrecks, and none
of shipwrecks are observed within the works area.
12.3.8.2
Marine disposal area
There are no known shipwreck sites located within the marine disposal area, but three
wrecksites are recorded some distance away, the nearest being the wreck of the Ashcrest
located some 575m SW of the disposal area (Figure 12.7). The Ashcrest was torpedoed in
1940, as was the Hans Broge in 1917 (Figure 12.8), wrecking some 12km away from the
disposal area. The third vessel is that of a modern trawler, the Lady Christine, which was lost
in 2003 and lies c. 3.8km from the disposal area.
12.3.9 Licensed archaeological work
The Excavations Bulletin publishes annual summary accounts of licensed archaeological
excavations undertaken throughout Ireland, which is currently published up to and including
2007.9 Summaries may also be submitted for inter-tidal survey, underwater assessments,
and the archaeological monitoring of marine dredging works (although the former two
categories are not required to be submitted for publication in the Bulletin). The entries
relating to the townlands surrounding Sligo Harbour are presented in Table A7.7 of Appendix
7A and Figure 12.4. There have been thirty-two events recorded. Fourteen of these projects
revealed nothing of archaeological significance. Of the remaining licenses, three were
granted for work within or on the site of known archaeological monuments. Many of the rest
revealed small-scale features such a burned spreads or ditch features, and do not contribute
additional relevant information to the current study. A small series of work has taken place in
Sligo town along the river bank and quaysides area, revealing a range of pre-existing
riverside features. Only three projects are reported in relation to marine activity, excluding
work on the Garvogue river itself. One was for a monitoring project associated with the
redevelopment of Raghly pier (Licence 07E0969). Another was for monitoring work
associated with the laying of a cable on Coney Island (no license number reported). The third
relates to the installation of a new timber jetty within Sligo Port, which required dredging to a
depth of 2.5m. A former timber pile was observed (08D079).
12.3.10
Conclusion
Maritime activity within Sligo Harbour is documented from early prehistoric times. The study
of the wider area indicates a range of sites and features that highlight an active awareness of
the importance of navigation into and out of the town, as a principal port on Ireland’s
northwest coast. The presence of prehistoric midden sites reveals foreshore activity.
9
Isabel Bennett (ed.) Excavations Bulletin: summary accounts of archaeological excavations in
Ireland, (Bray, Wordwell).
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Reference to known shipwrecking events highlights the Bungar Bank as a location where
wreckage debris can be expected to be observed, while the attention paid to establishing
safe access through the shallows of the inner harbour suggests an awareness of hazardous
access into Sligo. So too does the presence of twentieth-century wrecks on the mudflats.
While no archaeological material has occurred within the locations of proposed dredging,
there is an inherent potential for new archaeology to be revealed during capital dredging
projects along the approach channel to the port and on Bungar Bank. The potential was
confirmed within Sligo Port with the observation of a timber pile associated with the work to
insert a timber jetty in 2008. In such instances, there is a need for archaeological resolution
strategies, to mitigate the possibility for new discoveries.
The presence of three known wreck sites in proximity to the marine disposal area highlights
the need to assess the disposal area more fully for the presence of previously unrecorded
wreckage.
12.4
ARCHITECTURAL SITE ASSESSMENT
A desktop review of existing maps and historic photographs was supported by a series of site
visits in May 2011 (Appendix 7C) in the area around the harbour and around the shore at
Rosses Point near both Coney Island and Oyster Island, to see if any structures there could
be affected by the proposed dredging works.10 There are no protected structures in the area
of proposed development, and no structures of architectural heritage merit were observed in
the vicinity of the site where excavation work and dredging would take place. It can only be
concluded that work should be allowed to continue without any further investigation in
relation to architectural heritage or conservation proposals.
12.5
MARINE GEOPHYSICAL SURVEY
A marine geophysical survey was commissioned to contribute a further level of insight prior
to the commencement of the dredging and marine disposal operations. Such surveys
operate on the basis of emitting sonic pulses through the water column to detect material and
features on and under the seabed. It is usual to deploy a series of devices because each one
is designed to detect particular materials. The present project used two standard devices for
archaeological work: side-scan sonar and magnetometer, and was in compliance with the
requirements set by the DoEHLG for marine geophysical survey for archaeological purposes.
The survey was conducted along the approach channel, on Bungar Bank, and at the marine
disposal area. The work was conducted by Irish Hydrodata Ltd in April 2011, under licence
11R010. The primary data and associated mapping were examined by ADCO and the results
are presented below. Irish Hydrodata’s own report is included as Appendix 7D of this Report.
Side-scan sonar captures data to construct an image of the seabed surface over the area it
operates. It is an excellent device for mapping the seabed and for detecting hard anomalies,
such as those of stone and metal, and also of hard wood. It cannot detect material that is
10
A comprehensive statement of the architectural heritage assessment is presented as Appendix 7c of
the Report.
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buried, and it is difficult to observe soft woods because the sonic pulse passes through such
material without registering a difference with the ambient water. Magnetometers are used to
detect ferrous metal. In this they can complement the sonar by clarifying whether a sonar
contact contains significant metal – and is therefore manmade. Magnetometers also detect
anomalies below the seabed surface, and therefore can detect buried material. However,
unlike the sonar devices, magnetometers gather their information by emitting pulses directly
underneath; they cannot sweep the seabed from one side to the other as sonar does, and
consequently are limited to a vertical and near-vertical range of detection. The magnetometer
needs to pass more or less directly overhead of an anomaly to detect it.
12.5.1 Nature of record
The record is comprehensive. Side-scan sonar and magnetometer survey was conducted
over the survey areas. The following equipment was used:
x
L³-Klein System 3000 simultaneous dual frequency digital side-scan sonar system.
x
Geometrics G882 marine magnetometer (caesium)
12.5.2 Harbour
12.5.2.1
Survey Grid
The narrowness of the survey area resulted in two survey lines of data being acquired,
extending from the quays in Sligo Port to a point off the north side of Oyster Island (Figure
12.9). The lines were acquired in opposite directions to each other. Towards the western
extent of the survey area where the channel broadens sufficiently, the lines were spaced
90m apart, but were generally much closer to each other because of the confined nature of
the approach channel, and in places overlapped. Each line was set at a range of 75m. The
survey has provided ample overlap and the ability to view the same areas of seabed from
opposed directions.
12.5.2.2
Side-scan Sonar Survey
The data is generally very well defined. The bed area varies in consistency along the
surveyed route (Figure 12.10). There is a confused pattern of folded siltation at the quays
area, which gives way to a compacted hard bottom to the north as the approach channel
passes by Cartron and Ballincar townlands. The bed then retains greater amounts of siltation
as one proceeds through the harbour westwards, with patches of regular sand ripples
evident south of Rosses Upper.
The primary observations relate to the series of navigation aids, perches and markers that
define either side of the approach channel (a detailed list of side-scan sonar [ss] anomalies is
presented in Appendix 7D; see also Figure 12.13 - Figure 12.16). Those on the West and
South side of the channel survive as well-constructed circular mounds of foundation stones,
often measuring 10-12m in diameter and rising c. 3m in height (Figure 12.11). Lengths of
cable or chain are sometime apparent down one side. A training wall has been constructed
to link the perches on the south side of the approach channel as it crosses Middle Bank. The
sonar data clearly shows that building of the perches predates the training wall, and that the
wall is fractured in places. Anomaly ss5 represents the perch that defines the terminus of the
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training wall. A noticeable scour pocket has developed on the western or seaward side of the
perch, indicative of the exposed nature of the harbour area in this location. The navigation
aids on the North and East side of the channel are not as well defined but are nevertheless
clearly visible.
There are few indications of anomalies that cannot be explained in terms of the channel
markers. A series of anomalies were observed in this regard (Appendix 7D). All but one
occur as small-scale linear or irregularly-shaped features that are observed on the bed of the
approach channel, and may result from casual discard and are probably best described as
debris. In one instance however (ss25) the anomaly may be indicative of a more significant
feature. It survives as a c. 16m long negative anomaly that is long and narrow, almost boatshaped in form with a defined bow section and a stern section (Figure 12.12). It is 3.1m wide
at its centre. The anomaly is located at a point where the Cartron marsh enters the river. A
spread of stonework is evident on one side, while the anomaly itself is situated in silt. This
suggests the possible presence of a small quay area that is now inundated. The stonework
may also retain the base of a former navigation marker. It is some 70m from the recorded
location of the Gartsheerie that is pulled ashore. The magnetometer survey detected
elevated readings adjacent to the sonar anomaly, indicating the presence of a substantive
metal feature. The location is positioned adjacent to the proposed dredging area, and should
be assessed further for its archaeological potential.
Table 12.2 Side-scan sonar anomalies identified within the harbour area*
Reference
Description
Archaeological
Potential
ss25
Boat-shaped
negative
anomaly
measuring 16m long by 3.1m wide in the
middle, this feature has what appears to
be a defined bow and stern, and rests in
an area of silt directly against a stone
area that appears to be set, measuring
8m by 7m in size. Corresponds to mg9.
However the data presents it as a
negative image with no internal features
that one can expect of actual wreck
sites. It remains unclear what this image
is.
Unclear, possibly high
*Anomalies listed cannot be explained as modern features associated with the Port or as most likely
casual debris (for further information see detailed description, Appendix 7D).
12.5.2.3
Magnetometer Survey
The magnetometer survey was conducted in tandem with the side-scan sonar survey.
Overall, the survey has highlighted little evidence of natural background variation so that any
fluctuations observed most probably derive from human activity (a detailed list of
magnetometer [mg] anomalies is presented in Appendix 7D; see also Figure 12.13 - Figure
12.16). As can be expected, the survey conducted within the active port area produced
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excessively high levels of magnetic readings, reflecting the presence of working boats and
other devices. Elsewhere, the survey revealed a complementary sequence of localised
anomalies that correspond to the locations of the navigations aids. In a small number of
instances there was also a localised variation where no buoys or other navigation aids can
be identified. In those instances, the magnetic anomaly must derive from another metallic
source. Some of these locations correspond with sonar anomalies, indicating that the
anomaly lies exposed on the channel bed. In those instances where the magnetic anomaly
does not correspond with sonar data, it suggests that the magnetic feature is either very
small in scale and/or is buried. The results are presented in Table 12.3.
Table 12.3
Magnetometer anomalies identified within the harbour area*
Reference
Description
Archaeological
Potential
mg9
Extended intense fluctuation in magnetic
field over 28m-long area (recorded
reference point refers to the centre of the
highest readings). This anomaly is within
20m of the centrepoint of ss25 and
logically refers to the same feature.
Unknown, possibly high
* Anomalies listed cannot be explained as modern features associated with the Port (for further
information see detailed description, Appendix 7D).
12.5.3 Marine Disposal Area
12.5.3.1
Survey Grid
A 1km² grid was surveyed by running lines E-W in opposite directions, achieving a standard
zig-zag pattern of data acquisition. Lines spacing was set at 45m with range at 75m,
ensuring ample overlap. Because of the depth of the seabed in this location (approx. 90m),
particular set-up was required to ensure that the sonar towfish would be sufficiently weighted.
As indicated on Figure 12.17, the survey lines had to take account of sea-swell, but the close
spacing of the tracklines ensured that the full survey area was covered adequately.
12.5.3.2
Side-scan Sonar Survey
The underwater sea state intruded into the survey data, but the level of overlap in the survey
tracklines accounted for the intrusion. The seabed has a sandy/silty surface, with some sand
ripples noticeable (Figure 12.18).
Only a small number of anomalies were identified (a detailed list of side-scan sonar [ss]
anomalies is presented in Appendix 7D; see also Figure 12.19). The majority are probably
natural features and are considered as such. Two anomalies may represent manmade
remains. Anomaly ss307 is a well-defined isolated short linear object occurring in a sandy
area; it appears to be a piece of debris. Anomaly ss300 is poorly defined at the very north
end of the survey area, c. 100m north of and outside the defined disposal area. It is possible
to discern a boat-shaped profile, measuring 24.9m long x 5.9m wide. The anomaly is not
clearly visible, and it was not detected on the other survey lines, but it represents the only
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anomaly detected in the marine disposal area data that suggests the possible presence of in
situ wreckage debris. The magnetometer data does not indicate an anomaly, but it passed to
the south and may not have been able to detect the feature at that distance. Anomaly ss300
lies outside the defined limits of the disposal area and will therefore not be impacted on.
Table 12.4
Side-scan sonar anomalies identified on marine disposal area survey*
Reference
Description
Archaeological
Potential
ss300
A boat-shaped anomaly measuring
24.9m long x 5.9m wide, located c. 100m
north of disposal area. The data trace
shows a principal area of anomaly on
one side, with a less-clearly defined
tapering shape on the other.
Unclear, possibly high
*Anomalies listed cannot be explained as modern features or as most likely casual debris (for further
information see detailed description, Appendix 7D).
12.5.3.3
Magnetometer Survey
The magnetometer survey was conducted in tandem with the side-scan sonar survey. It
indicates a natural variation within the seabed deposits but few localized fluctuations
suggestive of manmade remains. Three anomalies in total were observed, each representing
very small-scale and localized fluctuations.
12.5.4 Conclusion
The area surveyed included the development areas and the channel to the north of the
jetties. Side-scan sonar and magnetometer surveys were conducted within the specifications
for marine geophysical surveys as defined by the DoA,H&G. The survey revealed the
navigation aids that line the approach channel to the Port. A single possible feature of
archaeological interest was observed within the harbour area, close to Cartron marsh, which
may represent the presence of a submerged iron wreck (anomaly ss25/mg9). However the
details are not entirely clear. A series of other anomalies were highlighted throughout the
areas surveyed. Correspondences of sonar contacts with magnetometer contacts indicates
metallic remains on the surface, while magnetometer targets in isolation indicate that there is
material buried beneath the covering sands. A single target identified adjacent to and outside
the marine disposal area may indicate the presence of a previously unrecorded feature
(ss300), but the nature is the data is not entirely clear. As it lies c. 100m outside the disposal
area, it will not be impacted upon.
The assessment and surveys conducted for the present report are very comprehensive, and
have not identified material of archaeological significance within any of the project impact
areas. There is no archaeological reason why the dredging works proposed should not
proceed.
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12.6
Cultural Heritage
PREDICTED IMPACTS11
To achieve the required dredging design, the alignment of the proposed dredge channel will
follow very closely the alignment of the existing channel. The proposed channel depth will be
to -3.0m CD. The proposed channel bottom width with be 50m with channel side slopes of 1
in 7. Of the 250,000m³ of material that it is proposed to dredge, 55% lies in the easterly
1500m of the channel nearest the town quays, while the bulk of the remaining 45% lies in the
westerly length of channel, which is approximately 2,200m long, from No 14 buoy to
Ballyweelin Point. The specific type of dredger to be used will not be known until a contractor
is appointed, but it is envisaged that either a suction dredger or a backhoe dredger will be
employed for the work. It is anticipated that dredging will proceed in an upstream direction,
and that dredging will be limited to the upper half of the tidal cycle.
The dredged material will be transported to the disposal area, where it is proposed to release
between 500m³ and 1,050m³ per dredging cycle. Modelling of the dispersion of the sediment
at the disposal area indicates that most of the deposited material will remain close to the
disposal site, with a small amount material migrating towards the east under the influence of
tidal action. The impact of the dumped sediments settling on the sea bed around the dump
site is not considered to be significant.
The dredging represents a direct impact on the seabed, and archaeological monitoring of the
dredging operation is recommended, to ensure the recovery of archaeological material that
may be recovered during the excavation works.
12.7
RECOMMENDATIONS
12.7.1 Pre-construction Measures
The need for further architectural heritage assessment for the dredging project is not
necessary as there will be no impact on features of architectural interest.
12.7.2 Construction Phase Measures
Dredging works will be take place as the primary activity of the present development.
Archaeological monitoring, licensed to the DoA,H&G is recommended during all works where
foreshore or seabed deposits will undergo removal. A suitably qualified competent maritime
archaeologist with experience in riverine/marine dredging environments should undertake the
archaeological monitoring. The archaeological monitoring should be undertaken with the
proviso for full excavation of any archaeologically significant material uncovered as part of
the operation. Licence processing takes a minimum of three working weeks to be processed
by the Department, and archaeologists cannot present on site before the licence is granted.
12.7.3 Archaeological/Cultural Heritage Management
x
Retaining an Archaeologist: a competent maritime archaeologist should be retained for
the duration of the relevant works. The time scale for the construction phase should be
11
Based on information from Chapter 4, “Project Description “and Chapter 11 “Coastal Processes” of
the Report.
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made available to the archaeologist, with information on where and when ground
disturbances and dredging will take place.
x
Sufficient notice: It is essential for the developer to give sufficient notice to the
archaeologist/s in advance of the construction works commencing. This will allow for
prompt arrival on site to monitor the ground disturbances. As often happens, intervals
may occur during the construction phase. In this case, it is also necessary to inform the
archaeologist/s as to when ground disturbance works will recommence.
x
Discovery of Archaeological Material: In the event of archaeological features or material
being uncovered during the construction phase, it is crucial that any machine work
cease in the immediate area to allow the archaeologist/s to inspect any such material.
x
Archaeological Material: If the presence of archaeologically significant material is
established, full archaeological recording of such material is recommended. If it is not
possible for the construction works to avoid the material, full excavation would be
recommended. The extent and duration of excavation would be a matter for discussion
between the client and the licensing authorities.
x
Archaeological Team: It is recommended that the core of a suitable archaeological team
be on standby to deal with any such rescue excavation. This would be complemented in
the event of a full excavation.
x
Archaeological Dive Team: It is recommended that an archaeological dive team be on
standby to deal with any underwater rescue excavation. This team will carry the
necessary commercial dive insurance, be fully certified to HSE/ HSA requirements, and
will conduct its work according to Safety in Industry (Diving Operations) Regulations
1981, SI 422, and 2010 SI (Draft), HSA Diving Standards 2010.
x
Secure wet storage facilities should be provided for the storage of archaeological
material derived from the marine environment within the project works compound.
x
Secure site offices and facilities should be provided on or near those sites where
excavation is required.
x
Fencing/buoying of any such areas would be necessary once discovered and during
excavation.
x
Adequate funds to cover excavation, post-excavation analysis, and any testing or
conservation work required should be made available.
x
Spoil should not be dumped on any of the selected sites or their environs.
Recommendations are subject to the approval of The Department of Arts, Heritage and the
Gaeltacht.
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12.8
Cultural Heritage
FIGURES
Figure 12.1: Admiralty Chart showing Harbour area and proposed dredging works
Figure 12.2: Admiralty Chart showing proposed marine disposal site.
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Cultural Heritage
Figure 12.3: Distribution of RMP sites in Harbour area.
Figure 12.4: Distribution of NIAH sites in Harbour area.
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Figure 12.5: Extract from 1859 sea chart showing the location of the Fancy.
Source: DoEHLG. Note: the wrecksite location is marked by a simple cross NW of Altconeen.
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Figure 12.6: Extracts from OS First Edition 1838 Sheet 14 and Third Edition
- the contrasting topographies of the inner harbour at Finisklin
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Figure 12.7: Map of known wrecksites in the vicinity of the marine disposal site.
Figure 12.8: The Hans Broge, before she wrecked, c. 1907.
Source: www.wrecksite.eu
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Figure 12.9: Marine geophysical survey tracklines within the Harbour area.
Outer harbour, S of Rosses
channel
at
Approach channel, S Approach
deepwater berths, indicating
of Ballincar
a timber pile jetty
Figure 12.10: Seabed images from the sonar data, Harbour area.
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Figure 12.11: Sonar trace showing the terminal perch, ss5.
Note the scour pocket that is developing at the seaward end of the perch. It is also possible
to observe that the training wall is constructed on top of the pre-existing perch foundation.
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Cultural Heritage
Figure 12.12: Sonar trace showing anomaly ss25 within its local context.
North is to the bottom of the image. The anomaly occurs as a tapering linear black feature
that lies against a stony shoreline. The stones appear to be constructed intentionally to
create a right-angled plan, and there is the suggestion of some mounding of stone to the left.
This complex of features may represent a former landing area on the east bank of the river,
close to Cartron marsh.
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Cultural Heritage
Figure 12.13:
Distribution of marine geophysical anomalies observed within the
Harbour area.
Figure 12.14:
Harbour area, East side.
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Figure 12.15:
Harbour area, central zone.
Figure 12.16:
Harbour area, West side.
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Figure 12.17: Marine geophysical survey tracklines at the marine disposal site.
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Figure 12.18: Sonar trace showing nature of seabed imaged at the marine disposal
site.
The sandy seabed with minor fluctuations is shown on the left side of the image. The dark
mottled space in the right side of the image refers to the water column through which the
sonar device is being towed, and the linear yellow line on the far right side is the sonar
trackline.
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Figure 12.19: Distribution of marine geophysical anomalies observed at the marine
disposal site.
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Human Beings
13.0 HUMAN BEINGS
13.1
INTRODUCTION
Several aspects of the well-being of the local community and the wider community within the
vicinity of Sligo Harbour have already been addressed within this Environmental Appraisal
Report:
x
x
x
Impact on commercial fishing activities – Chapter 7
Impact on air quality and noise – Chapter 8
Impact on material assets including traffic – Chapter 9
The potential impacts of the proposed dredging of the navigation channel are described in
detail within these chapters and, where appropriate, mitigation measures are presented.
This chapter of the Environmental Report details the human ‘environment’ of the hinterland of
the subject site in terms of population profile and trends, employment and community
aspects. It then discusses the impact of the proposed dredging on the overall amenity of the
area and puts forward a series of mitigation measures to offset any potential negative
impacts. This chapter of the Report describes how the proposed development will impact on
human beings in the surrounding area, in terms of tourism potential and socio-economic
profile.
13.2
SOCIO-ECONOMIC PROFILE
According to preliminary results from the 2011 Census enumeration (CSO, 2011) the
population of Ireland in 2011 was 4,581,269 persons, compared with 4,239,848 persons in
April 2006. This represents an increase of 341,421 persons since 2006, or 8.1 per cent. In
terms of annual average increase, this translates to an annual increase of 68,284 people, or
1.6 per cent.
Over the previous four-year inter-censal period between 2002 and 2006, the population
increased by 322,645 persons or 2 per cent per annum, which equates to an annual average
total of 80,661; the highest on record. This compares with 1.3 per cent for the preceding
inter-censal period 1996-2002 and the previous high of 1.5 per cent which occurred between
1971 and 1979. The 2011 population was last exceeded in the census of 1861 when the
recorded population was 4.4 million (CSO, 2007).
The very high births in the late 1970s and early 1980s, which reached a peak in 1980 with
74,000 births (today’s 31 and 32 year olds) is a strong distinguishing feature of the State’s
population pyramid (Figure 13.1), as is the sharp fall in births over the subsequent 15 year
period reaching a low point in 1994 (today’s 17 and 18 year olds). The recent recovery in
births, particularly in the last four years, is also clearly evident. The pyramid shape from age
30 and over reflects the effects of mortality as the population grows older (CSO, 2012).
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Human Beings
Within County Sligo, the population has risen by 4,376 persons in the five years 2006-2011
and now stands at 65,393. In percentage terms the increase (7.2 per cent) is marginally
below the State average of 8.1 per cent, but is significantly higher than neighbouring county
Mayo where the population rise is a more modest 5.4 per cent. The average for the entire
western region is 6.1 per cent (Western People, 2011).
A breakdown of the figures shows that the rise in Sligo’s population is fairly evenly spread
across the sexes with 2,263 females and 2,119 males making up the total of 4,376.
The population of Co Sligo now stands at its highest since World War II. After plummeting to
an all-time low of 50,275 in 1971 it has rebounded significantly in recent decades and one
has to go back to the census of 1936 to find a higher population for Co Sligo (67,447).
The population of the three electoral districts (Sligo East, North and West) comprising Sligo
city centre in the 2011 census (CSO 2012) was 17,568 (27% of the overall population of the
county). However, a further 18,145 people live in the wider Sligo city area, outside these
electoral boundaries but within 10 kilometres of the city centre, making a total of 35,713
people, or almost 55% of the county’s population living within 10km of the city centre
including the docks area.
More detailed population breakdown figures for Sligo are not yet available on the 2011
census, however the preliminary report on age breakdown across the County (CSO, 2012)
presents a population pyramid (Figure 13.1) showing that Sligo has very little fluctuation
across all age groups up to the elderly ages. The typical bend in the graph seen for the
State overall and centred around those aged 17 is compensated for by the presence of a
higher number of young people in the student years, no doubt due to the presence of third
level institutions.
Figure 13.1
State
Sligo County
Population pyramids (2011 census) for State and Sligo County
13-2
13.3
Human Beings
ECONOMIC PROFILE
13.3.1 Labour Force
Sligo serves as an administrative, employment, commercial, healthcare and education centre
for the North-West, which accounts for many of the professional services and administration
jobs in the area. The services sector is the primary employer in the City. Sligo also acts as a
distribution centre in the North-West and continues to retain a number of manufacturing jobs.
The IDA has two business parks in Sligo, one at Finisklin, next to the port, and another at
Cleveragh, which accommodate mainly knowledge-based industries and small engineering
companies. The pharmaceutical industry is significant, with several companies producing
goods for this sector (Sligo Co. Co., 2009).
Within broad occupational groups, professional, technical and healthcare workers are a
sizeable percentage of the labour force in Sligo at 18%, with clerical, managerial and
government workers forming 15.9% of the workforce.
This illustrates the importance of (decentralised) government agencies, local authorities and
the regional hospital as a source of employment.
Outside Sligo city, agriculture remains an important part of the local economy, though its
share of economic output and employment is declining. Other related industries such as
forestry, tourism and other rural-based economic activities are emerging and helping to
support the smaller towns and villages of the County.
Figure 13.2 Composition of Working Labour Force in Co. Sligo and State (2006)
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Human Beings
The Financial Crisis of 2008 affected the Irish economy severely, compounding domestic
economic problems related to the collapse of the Irish property bubble. Unemployment
within the State has risen sharply since 2008 (Figure 13.3) from levels of around 4.5% to
over 14%. Many of these job losses have occurred within the construction, property and
financial sectors. The economic climate has also led to increased emigration.
Figure 13.3
State Unemployment Rate
Figure 13.2 shows the composition of the working labour force, as presented in the 2006
census in County Sligo (2011 figures were not yet available at the time of writing). It can be
seen that although the majority of the labour force in Sligo at that time worked in service
industries, a significant proportion worked in Manufacturing (13.3%), Construction (11.5%)
and Wholesale and Retail Trade (12.6%). These occupations (which comprised more than
37% of the workforce in Sligo in 2006 but realistically are expected to be significantly less in
2011) could benefit from development of the port and increased economic activity resulting
from the proposed dredging. The ability to export directly by sea from Sligo could also assist
in attracting new manufacturing businesses to the area.
13.3.2 Fisheries and Aquaculture
There are several licenced aquaculture sites operating within the boundaries of the Harbour,
(although not all are currently actively farmed) with further aquaculture sites within Drumcliff
Bay and Ballysadare Bay (refer to Chapter 7 “Fisheries and Aquaculture”). The local
employment in fisheries and shellfish will remain unaffected, as impacts are not anticipated
to extend beyond the dredging area (also see Chapter 11, “Hydrodynamic Modelling”).
Fishing, as well as potting for lobster and crab also take place within Donegal Bay, including
the area of the proposed offshore dump site. The predicted impacts on fisheries are also
discussed in more detail in Chapter 7, “Fisheries and Aquaculture” and are not expected to
be significant.
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Human Beings
13.3.3 Sligo Port
The economic inputs of Sligo Port are discussed in more detail in Chapter 1.2 “Project
Justification”. Whilst the number of vessels berthing at the port each year has remained
fairly constant, the tonnages transported by these vessels has been increasing steadily.
However, the channel depth is posing a constraint on the future viability of these transport
routes as without dredging these vessels will have to reduce their cargo load to allow
adequate clearance, which may threaten their economic viability. As described in Chapter
1.2, more than 180 jobs are directly dependent on the Port and the indirect benefits extend to
an much wider range of industries. Should the existing cargo vessels be forced to berth at
other ports, it is estimated that €2 million of disposable income would be lost to Sligo Town
and its environs. This would have a major negative impact on local retailers, restaurants and
other services.
13.4
TOURISM
Sligo is part of the north west tourism region, which also encompasses the counties of
Cavan, Donegal, Leitrim and Monaghan. The most recent available regional tourism figures
are from 2009, during which there were 1.4 million tourist visits, generating €319 million in
revenue. Approximately half of the visitors (754,000) were domestic trips made by Irish
residents, earning the region €115 million in revenue. Another significant proportion of
visitors came from Northern Ireland, whose residents made 254,000 visits to the north west,
spending €64 million.
Overseas visitors make a significant contribution to the economy of the north west, having a
much higher per capita spend during their visits. Figure 13.4, from Failte Ireland, shows
annual overseas visitor figures to the north west region between 1999 and 2009. Overseas
visitor numbers dropped substantially in 2001-2002, a pattern reflected in tourist figures
throughout Ireland and not just the north west. The reduction in numbers of overseas visitors
during this period was attributed principally to the outbreak of Foot & Mouth Disease in
Britain in February 2001 and the terrorist attacks on the United States in late 2001. These
events brought to an end the growth trend that had developed across the whole of Ireland
over the previous nine years. From 2002 visitor numbers gradually rose again, however it
can be seen in Figure 13.4 that the global financial crisis in 2008 has had a significant impact
on overseas visitor numbers with a substantial drop in numbers in 2009.
13-5
Figure 13.4
Human Beings
North West Region Overseas Visitor Numbers 1999-2009
Failte Ireland, 2010
Sligo is the second most visited county in the north west region after Donegal (Table 13.1)
Table 13.1
Visitor numbers/revenue north west region 2009
Visitors ‘000s
Revenue € million
Cavan
72
30
Donegal
161
43
Leitrim
27
14
Monaghan
32
12
Sligo
142
42
Figures provided by Failte Ireland (2010) state that angling tourism brought 132,000
overseas visitors to Ireland in 2009 (2% of all visitor numbers) and generated an estimated
spend of €105 million. Golf tourism attracted a further 146,000 overseas visitors (2.2% of all
visitor numbers) generating an estimated spend of €110 million. These activities form a
much greater proportion of the tourism in the north west region, but the Failte Ireland figures
do not include figures from domestic or Northern Ireland tourists, many of whom would travel
to the north west to engage in these activities while on short trips.
Economically tourism is very important to Co. Sligo and provides much needed revenue and
employment, especially in remote rural areas. Golf and fishing therefore form an extremely
important sector of the economy within this region, with other outdoors activities such as
surfing, horse riding and hiking making smaller but nonetheless significant contributions to
the tourism revenue.
13-6
Human Beings
The government sees tourism as a key sector in rebuilding the Irish economy. Whilst the
main aims are to re-attract the lost numbers of tourists from Britain and overseas, there are
significant opportunities to expand within the domestic market and Northern Ireland as
reduced incomes in these areas may prompt families to choose a domestic destination for
their holidays in favour of travelling overseas. This has been helped by cuts in the VAT rate
for restaurants, hotels and tourist attractions from 13.5% to 9% from 2011-2013.
One of the target areas for Tourism Ireland is sea angling, where a group of anglers would
hire a boat and the focus is on catching big fish offshore. The focus is on anticipation of how
big the fish will be rather than the effort/techniques and the main potential market is the
domestic/UK market. In this respect these groups require experienced skippers and usually
have an all-in deal with hotel accommodation (Failte Ireland, 2005).
The potential impact of the proposed dredging on fish and fisheries within the Garavogue
Estuary and the wider Sligo Harbour/Donegal Bay area has been examined in detail in
Chapter 7 – Fisheries and Aquaculture. There will be some limited disturbance during the
dredging activities but these will be temporary in nature and will not pose any significant
impact to recreational or commercial game fishing within the Garavogue River, Lough Gill or
the wider Sligo harbour area.
A recent report commissioned by businesses in Sligo (O’Rourke, 2012) criticises the failure
of Sligo to capitalise on its natural resources as a tourism attraction. Whilst the city itself has
less potential as a tourist attraction, its wealth of quality hotels, bars and restaurants mean
that it is more than equipped to serve as a focal point and base for a successful tourism
industry, linked to the county’s resources of landscape and archaeology.
The O’Rourke report also describes the impact of the Economic Collapse on the retail sector
in Ireland as being “profound”. CSO figures indicate that the total value of retail sales fell by
24% between 2007 and 2011. The fall in sales has not been uniform over the different
sectors of retailing with families concentrating on buying “basics” and cutting down on all
luxury or discretionary expenditure. Sales in Pubs fell by 28% over the period 2007 to 2011
with the fall in sales in some sectors even bigger with a 33% decline in sales in Books and
Newspaper Stores and a 52% decline in sales in Furniture Stores. Tourism is one of the few
industries which has real potential for rapid growth in business activity and employment in
Sligo over the next five years. An increase in tourism will boost employment directly, but will
also support the retail sector which has suffered such a rapid decline in Sligo.
The O’Rourke report makes recommendations for inexpensive improvements to increase
access to the county’s natural resources, such as improving access to sites such as
Benbulben, creating a cycle path network linking the attractions within Strandhill peninsula
and Rosses Point and improving signage to visitor attractions throughout the county. The
report does not make specific recommendations towards maritime tourism, however the
enhancement in accessibility of the navigation channel coupled with the establishment of the
pontoons at the Timber Jetty could create a more rounded tourism experience, where
perhaps visitors could take a boat ride to Rosses Point and subsequently return to the city by
bicycle. In addition, added opportunities for sea angling could be created, as skippers will be
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Human Beings
able to pick up groups of anglers from the city centre for trips offshore at all stages of the
tide.
13.4.1 Bathing Waters
Rosses Point beach, just north of the entrance to Sligo Harbour, is a designated bathing
water and also holds Blue Flag and Green Coast awards. The EPA monitors designated
bathing waters in Ireland against standards in the Bathing Water Quality Regulations 2008
(as amended 2011) which are derived from the EC Bathing Water Directive (76/160/EEC).
Further information on water quality in the context of the EC Bathing Water Directive is
presented in Chapter 14, “Sediment and Water Quality”.
The commissioning of the new waste water treatment works in Sligo has had a significant
positive effect on water quality within the harbour. There are not anticipated to be any
negative impacts associated with the dredging activities within the harbour at Rosses Point
beach; the dredging activities will not contribute to any increase in bacteriological activity and
the influence of other parameters such as turbidity will not extend outside the confines of the
harbour.
13.4.2 Sailing
Sligo has a vibrant marine recreation and leisure culture. Activities such as sailing,
windsurfing, angling, motor boating and rowing are available in Sligo Harbour. Sligo Yacht
Club is located at Rosses Point and hosts competitions in three classes:
x Cruisers
x GP 14s
x Mirrors
with two further classes, Optimist and Laser being promoted (Sligo Yacht Club, 2012).
Sailing takes place 5 days a week between April and October with sailing activities
concentrated outside the harbour in Sligo Bay.
The World Championships for the Mirror class were held at Rosses Point in 1987 and it also
hosted the European Championships more recently in 2010. Rosses Point is one of the
locations competing to again host the Mirror class World Championships in August 2013. In
June 2011 over 100 boats competed in a fortnight long International and World
Championship event for the Fireball class, which was held at Sligo Yacht Club.
These sailing events provide a significant boost to the local economy with sailing teams, their
families, support staff and sponsors staying in local accommodation.
The Fireball
championships also coincided with a series of fringe events such as a Sea Shanty and
Seafearing festival (Sligo Champion, 2011), which attracted significant numbers of local
visitors who would not normally attend sporting events.
As the dredging is to take place within Sligo Harbour, outside the main sailing area, it is
expected that there will be limited impacts to recreational sailing. During dredging, there will
13-8
Human Beings
be an exclusion zone set up around the dredger for safety reasons. This will cause a
temporary restriction to leisure craft using the area of the harbour within the immediate
vicinity of the dredger.
It is recommended that Sligo County Council sets up a liaison with Sligo Sailing Club and any
other clubs with significant numbers of leisure craft users in the harbour to facilitate a safe
co-existence between the dredger and leisure craft. Timetables showing the programmed
dredging activity should be published locally giving adequate advance notice of the areas
that will be affected.
13.5
CONCLUSIONS
13.5.1 Predicted Impacts
The proposed dredging at Sligo harbour will have no negative impacts on the existing
tourism and retail industries in Sligo and should have a positive impact on both sectors upon
completion of the works. During the dredging operations, there may be some temporary
minor disruption to using leisure craft within the harbour, depending on the time of year the
dredging takes place.
13.5.2 Mitigation Measures
Sligo County Council will establish a mechanism for liaison with the local sailing clubs and
recreational users of the harbour. Harbour users will be informed of the programme of works
anticipated over the dredging period, e.g. by newspaper notices and information boards at
slipways and launching sites.
Of particular importance will be the requirement to coordinate with local sailing organisations
to ensure that dredging activities do not pose a conflict with any scheduled major sailing
events.
13.5.3 Residual Impacts
Around 180 jobs directly linked to the port’s commercial activity will be safeguarded by the
proposed dredging works. There is potential for increasing employment both directly and
indirectly as it is hoped that the scheme will become a catalyst to boost tourism and
commercial activity within Sligo city and the wider Sligo Harbour area.
13-9
Human Beings
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13-10
Water Quality and Sediment
14.0 WATER QUALITY AND SEDIMENT
This chapter describes the potential impacts of the proposed dredging in relation to the
marine sediments and water quality. The study area for this assessment is Sligo Harbour,
the Garavogue Estuary1 and the eastern section of Sligo Bay.
14.1
Overview of Existing Legislation
Water Quality data within the study area is monitored by the Environmental Protection
Agency (EPA), the Local Authority and the Marine Institute in response to the following
legislation:
x
x
x
EC Bathing Waters Directive (76/160EEC)
EC Shellfish Waters Directive (2006/113/EC)
EC Water Framework Directive
Monitoring data are then compared against environmental quality standards (EQS) which are
designed to protect the environment and human health. Monitoring is also carried out for
compliance with the EC Urban Waste Water Treatment Directive (91/271/EEC).
The nearest designated bathing water to Sligo Harbour is Rosses Point, which is
approximately 2km from the westernmost limit of the dredging area (Figure 14.1). Rosses
Point is also a Blue Flag beach, although it temporarily lost its blue flag between 2008 and
2010 due to failing to meet the guideline (higher) standards for faecal coliforms in a small
minority of samples taken in 2007 and 2008. County Sligo has two further designated
bathing waters at Enniscrone and Mullaghmore, both of which are more than 5km from the
proposed dredging area and are therefore outside the study area for this Environmental
Report.
Figure 14.1: Designated Bathing Water
1
Garavogue is intentionally spelled a number of different ways in this section, dependent on the spelling used in the source documentation. E.g. the WFD waterbodies are
named “Garavoge Estuary” and “Gill, tributary of Garavogue” in the Local Authority’s River Basin Management Plan.
14-1
14.1.2 Shellfish Waters
In 2009, the Department of the Environment, Heritage and Local Government designated
Sligo Bay and Drumcliff Bay (Figure 14.2) as shellfish areas in accordance with the Shellfish
Waters Directive 2006/113/EC and the European Communities (Quality of Shellfish Waters)
Regulations 2006 (as amended 2009).
Sligo Bay has been listed as a Class B (oysters and clams) bivalve mollusc production area
in the Sea Fisheries Protection Authorities (SFPA) publication “Classified Bivalve Mollusc
Production Areas in Ireland” (2009)”. Drumcliff Bay has also been assigned Class B status
as a production area for mussels, oysters, clams and cockles.
Figure 14.2: Sligo Bay and Drumcliff Bay EC Designated Shellfish Waters
Class B areas are areas from which live bivalve molluscs may be collected, but placed on the
market for human consumption only after treatment in an approved purification centre, or
after relaying relaying in an approved relaying area, or after an EC approved heat treatment
process.
The Sligo Bay designated shellfish water covers an area of 8.6km². The dredging area
ranges from approximately 130 metres at its closest point to 500 metres from the designated
area. Drumcliff Bay shellfish water is more than 3km at its closest point from the dredging
area. The Marine Institute undertake water quality sampling at a station in the eastern
portion of the shellfish area, within one of the licensed clam areas (Figure 14.2).
14-2
Compliance with the Directive is measured against achievement of shellfish water quality
parameter values outlined in Annex I of the Shellfish Waters Directive (2006/113/EC) which
was transposed into Irish law under the European Communities (Quality of Shellfish Waters)
Regulations 2006 - Schedules 2 and 4. Schedule 2 Mandatory values must be fully
achieved, while it must be endeavoured to achieve Guideline values (Schedule 4).
The Regulations in Schedule 4 include a Guide value for faecal coliforms in the shellfish
flesh, but there is no standard or guide value for faecal coliforms in ambient water.
The DOEHLG has published Pollution Reduction Programmes for both Sligo Bay and
Drumcliff Bay which must be implemented by Sligo County Council.
14.1.2.1
Sligo Bay Pollution Reduction Programme (PRP)
The DoEHLG’s Sligo Bay Pollution Reduction Programme (PRP) for this designated shellfish
area was signed into effect by the Minister in December 2009. Under this programme the
Marine Institute is required to carry out a monitoring programme to monitor the condition of
waters in the shellfish growing area and to verify compliance, or otherwise with the water
quality standards outlined in Schedules 2 and 4 of the Quality of Shellfish Waters
Regulations (S.I. No. 268 of 2006) The Marine Institute submits a report on water quality in
respect of the designated area to the Minister each year, and brings to the attention of the
Department any non-compliance with a water quality standard.
UV treatment to protect the shellfish waters has been in place on the primary discharge since
the commissioning of the new WWTP in January 2009.
14.1.3 The Water Framework Directive
Directive 2000/60/EC, establishing a framework for Community action in the field of water
policy (the Water Framework Directive), was adopted by the European Parliament and
Council in 2000. It was transposed into Irish law via the European Communities (Water
Policy) Regulations, 2003 (S.I. No. 722 of 2003), as amended by the European Communities
(Water Policy) (Amendment) Regulations, 2005.
The Water Framework Directive (WFD) creates a legal framework for the protection,
improvement and sustainable management of rivers, lakes, transitional waters (estuaries),
coastal waters and groundwater. It is an over-arching piece of legislation, superseding and
updating existing legislation, and will be the most significant piece of legislation governing the
water environment for the foreseeable future.
The aim of the WFD is to prevent deterioration of the existing status of waters and to ensure
that all waters are classified as at least ‘good’ status (by 2015 in most cases, with all waters
achieving good status by 2027 at the latest). A water body must achieve both good
‘ecological status’ and good ‘chemical status’ before it can be considered to be at good
overall status.
The proposed dredging area extends across two water bodies (Figure 14.3):
14-3
x
x
Garavoge Estuary transitional water body (water body code: IE_WE_470-0100)
Sligo Harbour coastal water body (water body code: IE_WE_470-0000).
Two further water body boundaries are within close proximity to the proposed dredging area
and may also be influenced by the proposed project. These are:
x
Sligo Bay coastal water body (code: IE_WE_450-0000)
x
Gill, tributary of Garavogue (code: IE_WE_35_4183)
Figure 14.3: Water Framework Directive Water Body Boundaries and Overall Status
Sligo Harbour also holds SAC, SPA and EC shellfish water designations. The water quality
requirements for these areas relating to the Habitats, Birds and Shellfish Water Directives
are discussed separately in Chapter 6, Intertidal & Marine Flora and Fauna, Chapter 5, Birds
and Chapter 7, Fisheries and Aquaculture respectively.
This section presents surface water quality information for the waters in the vicinity of Sligo
Harbour where the dredging works are proposed. The sources of the water quality
information summarised in this chapter are:
x
Water body status information arising from the Water Framework Directive monitoring
programme and outlined in the Western River Basin Management Plan (2009-2015)
(WRBD, 2010).
x
Water quality information outlined in the EPA’s most recent water quality report, “Water
Quality in Ireland 2007-2009” (EPA, 2011).
14-4
14.1.3.1
WFD Status Classifications
Environmental Quality Standards (EQSs) for classifying surface water status are established
in the European Communities Environmental Objectives (Surface Waters) Regulations, 2009
(S.I. 272 of 2009). These regulations set standards for biological quality elements,
physicochemical conditions supporting biological elements (including general conditions and
specific pollutants), priority substances and priority hazardous substances.
The ‘ecological status’ of a water body is established according to compliance with the EQS
for biological quality elements, physico-chemical conditions supporting biological elements
and relevant pollutants.
The ‘chemical status’ of a water body is established according to compliance with the EQS
for priority substances and priority hazardous substances.
As well as achieving good ecological and chemical status, a water body must achieve
compliance with standards and objectives specified for protected areas, which include areas
designated by the Bathing Water, Urban Waste Water Treatment, Shellfish Waters, Habitats
and Birds Directives. Waters bodies that are compliant with WFD standards, but that contain
protected areas that are non-compliant with protected area standards, are downgraded to
‘less than good’ status.
In order to establish the WFD status of water bodies, the EPA developed a new, WFD
compliant monitoring programme which began in 2006. It builds on previous monitoring
programmes and provides a comprehensive assessment of water quality and quantity. WFD
status classifications apply at the water body scale and are based on several
samples/surveys targeting the variety of parameters, including biological, physico-chemical,
chemical and hydromorphological elements, required to establish WFD status. The current
status classification is based on monitoring information collected between 2007 and 2009
(EPA, 2011). The final status classifications, based on the results of this complete monitoring
cycle, i.e. 2007 to 2009, were reported in 2011 (EPA, 2011).
The status classification of transitional and coastal water bodies is primarily based on
information and data collected by the EPA, Marine Institute and Central Fisheries Board (now
Inland Fisheries Ireland) between 2007 and 2009. In addition, assessments of the
conservation status of protected areas carried out by NPWS are also taken into account.
14.2
EXISTING WATER QUALITY
Pre 2011, bathing water compliance assessment was based on five microbiological and
physicochemical parameters as required under the 1992 “Quality of Bathing Waters
Regulations”. From 2011 onwards, bathing water compliance is assessed under the
requirements of the 2008 “Bathing Water Quality Regulations” which only monitors two
14-5
microbiological parameters; Intestinal enterococci and Escherichia coli. For the 2011 bathing
season, Rosses Point Beach achieved good water quality status and complied with both the
EU guideline and mandatory values (Figure 14.4 - EPA, 2012). Rosses Point Beach also
achieved good water quality status in the periods 2009 to 2010 and 2003 to 2006 but only
had “sufficient” water quality status in the period 2007 to 2008.
Source: Splash! www.bathingwater.ie
Figure 14.4: Bathing Water Quality Status
The loss of the Blue Flag in 2008 was in part due to adverse weather conditions, but also the
lack of adequate foul waste treatment for Sligo city up to that year. Since the commissioning
of the Sligo waste water treatment plant in 2009, the water quality has risen significantly,
allowing the Blue Flag to be reinstated in 2010 after the beach had achieved the guideline
standard for two consecutive years. With the treatment plant operational, Rosses Point has
comfortably exceeded both the mandatory and guideline water quality targets since 2009.
14.2.2 Shellfish waters
Monitoring of seawater from the designated areas is carried out by the Marine Institute, who
provided RPS with water quality measurement data acquired between 2007 and 2012.
During this time, the water quality in the shellfish waters was generally very good and
comfortably exceeded the guideline values for shellfish waters. The EPA “Water Quality in
Ireland 2007-2009”, Chapter 5 “Quality of Estuarine and Coastal Waters” also confirms that
levels of trace metals in shelfish tissue were also well within EU limits for this period.
Monitoring for microbiological criteria such as levels of E. coli in shellfish waters as well as
phytoplankton and marine biotoxins takes place on a more frequent weekly or monthly basis
and no issues with microbiological tests have been reported in the 6 months to June 2012
(Marine Institute, 2012).
14-6
14.2.3 The Water Framework Directive
The EPA Water Water Framework Status Update based on Monitoring Results 2007-2009
was published in 2011 and presents a review of Irish ambient water quality for the years
2007 to 2009.
The water quality information in relation to transitional and coastal waters outlined in the
report was generated by the EPA as well as other organisations including:
x
x
x
x
x
x
Central and Regional Fisheries Boards (now Inland Fisheries Ireland);
Marine Institute;
Sea Fisheries Protection Authority (SFPA);
National Parks and Wildlife Service (NPWS);
Waterways Ireland; and
Irish Coast Guard.
A water body must achieve both good ‘ecological status’ and good ‘chemical status’ before it
can be considered to be at good overall status. It must also be compliant with standards for
protected areas in the vicinity. The extents of each of the water bodies have been shown
above in Figure 14.3 (on page 14-4).
14.2.3.1
Garavoge Estuary
As shown in Table 14.1, the Garavoge Estuary water body achieved “high” status in relation
to many of the physico-chemical and biological parameters and is compliant with the
standards established in the Habitats and Birds Directives. However, the Garavoge Estuary
failed to achieve overall ‘high’ status due to below high status threshold values measured for
Dissolved Oxygen and therefore was only classified overall as having achieved “good”
status. The water body has been rated as being “1b - probably at risk” of failing to achieve
“good” or “high” status by the end of the WFD cycle in 2015 and its overall objective in the
RBMP is therefore to “protect” the existing status (or improve upon it).
14.2.3.2
Sligo Harbour
Sligo Harbour water body is incorrectly reported in the wfdireland water maps tool as having
achieved “high” status. The tool may not yet have been fully updated following last year’s
publication of the 2007-2009 results. Although the waterbody achieved high status for
almost all the criteria (Table 14.1) and is compliant with the standards established in the
Birds and Habitats Directives, it only achieved “good” status for its morphology due to its
phytoplankton measurements. This status reduces the overall classification to “good” as the
WFD operates on a One Out – All Out (OOAO) basis The water body has been rated as
being “1a - at risk” of failing to achieve “good” or “high” status by the end of the WFD cycle in
2015 and its overall objective in the RBMP is therefore to “protect” the existing status (or
improve upon it).
14-7
Table 14.1: Site Area Transitional and Coastal Waterbody Status
Status Element Description
Status Information
Dissolved Inorganic Nitrogen status
Molybdate Reactive Phosphorus status
Dissolved oxygen as per cent saturation status
Biochemical Oxygen Demand (5-days) status
Macroalgae - phytobiomass status
Macroalgae - opportunistic algae status
Macroalgae - reduced species list status
Angiosperms - Seagrass and Saltmarsh status
Benthic Invertebrates status
Fish status
Hydrology status
Morphology status
Specific Pollutant Status
Overall protected area status
Ecological Status
Chemical Status
Surface Water Status
Extrapolated status
Donor water bodies
OVERALL STATUS
Garavoge
Estuary
Result
Sligo Harbour
Result
Sligo Bay
Result
High
High
Good
High
High
N/A
N/A
High
N/A
Good
N/A
Good
Pass
At least good
Good
Pass
N/A
N/A
N/A
GOOD
High
High
High
High
High
N/A
N/A
N/A
N/A
N/A
N/A
Good
N/A
At least good
High
N/A
N/A
N/A
N/A
GOOD
High
High
High
High
High
N/A
High
N/A
N/A
N/A
N/A
High
N/A
At least good
High
N/A
N/A
N/A
N/A
HIGH
N/A = not assessed
Source: wfdireland.com& EPA (2011)
Table 14.2: Site Area River water body status
Gill, Tributary of
Garvogue
Result
Status Element Description
Status information
Macroinvertebrate status
General physico-chemical status
Freshwater Pearl Mussel / Macroinvertebrate status
Diatoms status
Hydromorphology status
Fish status
Specific Pollutants status (SP)
Overall ecological status
Overall chemical status (PAS)
Extrapolated status
Monitored water body
Donor water bodies
OVERALL STATUS
N/A = not assessed
14.2.3.3
High
Good
N/A
N/A
Good
N/A
N/A
Good
n/a
N/A
YES
N/A
GOOD
Source: wfdireland.com& EPA (2011)
Sligo Bay
As shown in Table 14.1, Sligo Bay water body achieved “high” status in relation to all of the
physico-chemical and biological parameters and is compliant with the standards established
in the Habitats and Birds Directives. The water body therefore was awarded “high” status
overall. The water body has been rated as being “1a - at risk” of failing to achieve “good” or
“high” status by the end of the WFD cycle in 2015 and its overall objective in the RBMP is
therefore to “protect” the existing status.
14-8
14.2.3.4
Gill, Tributary of Garvogue
As shown in Table 14.2, the Gill, Tributary of Garvogue water body achieved “good” status in
relation to all but one of the physico-chemical and biological parameters. The water body
therefore was awarded “good” status overall. The water body has been rated as being “2b –
not at risk” of failing to achieve “good” or “high” status by the end of the WFD cycle in 2015
and its overall objective in the RBMP is therefore to “protect” (or improve) the existing status.
14.2.3.5
Trophic Status
The trophic status of transitional and coastal water bodies is assessed using the EPA’s
Trophic Status Assessment Scheme (TSAS). This assessment is required for the Urban
Waste Water Treatment Directive and Nitrates Directive. The scheme compares the
compliance of individual parameters against a set of criteria indicative of trophic state (DIN,
MRP, chlorophyll, macroalgae, dissolved oxygen). These criteria fall into three different
categories which broadly capture the cause-effect relationship of the eutrophication process,
namely nutrient enrichment, accelerated plant growth, and disturbance to the level of
dissolved oxygen normally present;
x
x
x
x
Eutrophic water bodies are those in which criteria in each of the categories are
breached, i.e. where elevated nutrient concentrations, accelerated growth of plants
and undesirable water quality disturbance occur simultaneously;
Potentially Eutrophic water bodies are those in which criteria in two of the
categories are breached and the third falls within 15 per cent of the relevant threshold
value;
Intermediate status water bodies are those which breach one or two of the criteria;
Unpolluted water bodies are those which do not breach any of the criteria in any
category.
“Water Quality in Ireland 2007-2009” (EPA, 2010) has published the most recent trophic
status for the transitional and coastal waterbodies around Ireland. Since the previous report
in 2005, five water bodies have improved from intermediate to unpolluted status and these
include the Garavogue Estuary, Sligo Harbour in addition to Kinsale Harbour, McSwyne’s
Bay and the Lower Liffey estuary. This marked improvement in status is directly attributable
to the commissioning of the Sligo WWTP.
14.2.3.6
Dissolved Oxygen Levels
Low levels of Dissolved Oxygen (DO) can have adverse effects on aquatic organisms
including slower growth rates, impaired immune response and, in severe cases, mortality.
DO levels are classified as follows:
x Anoxic (0 - 0.5 mg l-1)
x Hypoxic (0.5 – 2.0 mg l-1)
x Deficient (2.0 – 6.0 mg l-1)
x Sufficient (6.0 – 10.0 mg l-1)
14-9
Sligo Harbour water body has been measured as having “sufficient” Dissolved Oxygen levels
during sampling. The Garavogue Estuary has had some “deficient” results which lowered its
WFD DO status to “good”.
14.3
Sediment Quality
14.3.1 Dredging Area – Sediment Chemical Properties
As the approximately 250,000 cubic metres of dredged material is to be disposed of at sea,
sediment contamination testing was undertaken for fourteen marine sediment samples taken
within and adjacent to the dredging area, to ensure that disturbance of these sediments
would not pose a threat of releasing contaminants.
Consultation was held with the Marine Institute, Galway, to determine location stations,
parameters and detection limits for contamination testing, in accordance with the Guidelines
for the Assessment of Dredge Material for Disposal in Irish Waters” (2006).
The sampling programme was undertaken by Aqua-Fact International Services in September
2009. Surface samples were taken by means of a 0.025m² VanVeen grab for subsequent
contaminant analysis, organic carbon content and granulometric analysis. When samples
were recovered on board from each station, notes were logged on sediment type, amount,
colour and smell (Table 14.3).
Granulometric analysis was undertaken by Aqua-Fact in their laboratory.
Sub-samples were sent to the UK Environment Agency’s National Laboratory Service Facility
at Leeds for chemical contaminant analysis of the sand-mud fraction (Ø<2mm). Appropriate
marine Certified Reference Material (CRM) was analysed alongside the samples to ensure
calibration.
Additional samples were also taken from 5 stations (St1, 4, 7, 10 & 12) and were sent to the
Radiological Protection Institute of Ireland for radiological analysis.
14.3.1.1
Sampling Station Locations
The sample locations were specified by the Marine Institute as presented in Figure 14.5.
14-10
Figure 14.5: Sligo Sediment Chemical Sampling Stations
Table 14.3: Dredging Area Sediment Samples - Descriptions
Station
ID
Colour
Smell
%
Water
1*
black/grey Mud
Weak
H2S
72.9
2*
black/grey Mud
Weak
H2S
61.0
3*
black/grey Mud
Weak
H2S
70.2
14-11
4*
Grey/brown
Mud
none
66.6
5
Grey/brown
Muddy sand
none
54.4
6
Grey/brown
Muddy/sand
none
64.3
7
Brown/grey
Sand
none
30.1
8
brown/grey
Sand
none
24.9
9
Grey
Muddy sand
none
56.4
10
Brown/grey
sand
none
21.6
11
Brown/grey
sand
none
25.6
12*
Brown/grey
sand
none
16.4
14-12
* Asterisked Stations are located outside the final dredging area (Stations 1-4 and Station
12)
14.3.1.2
Sediment Quality Results
The results of the granulometric analysis showed that the surface sediments in the inner
harbour area (Stations 1 – 4) were typically made up of fine mud with varying amounts of fine
sand. Consistent with the vibrocore results, the sediment samples collected in the outer
harbour had increasingly higher grain size content (Stns 5 – 12).
The results of the contamination analysis showed compliance with the guideline limits
proposed by the Marine Institute and DCMNR in the publication “Guidelines for the
assessment of dredge material for disposal in Irish Waters” (2006) with the exception of Stn
1, which had elevated Polycyclic Aromatic Hydrocarbons (PAH) levels.
PAHs are one of the most widespread organic pollutants occurring in oil, coal and tar
deposits and are produced as a by-product of fuel burning. In addition to their presence in
fossil fuels they are also formed by incomplete combustion of carbon-containing fuels such
as wood, coal, diesel, fat, tobacco so they can come from many sources. PAHs in the
environment are found primarily in soil sediment, but can also be found in water.
The results of the sediment quality sampling and analysis programme were sent to the
Marine Institute for their review and comment. The Marine Institute reverted with a
requirement to undertake additional PAH analysis. The results of the additional analysis are
also presented in Appendix 8. These additional results were sent to the Marine Institute for
further review and comment.
The most likely source of the elevated PAH levels was a ship which caught fire in the
upstream portion of the port. Although the ship has been removed, residual contamination
may remain in the upper part of the channel. The sampling results confirm that this
contamination is localised only to the immediate area of the channel surrounding the former
location of the vessel.
As the upper part of the channel, above the Barytes and Deepwater jetties is only in use by
recreational vessels which have a much smaller draft than the commercial vessels, there are
no immediate requirements to dredge this part of the channel. Therefore, in consultation with
the Marine Institute it was agreed that dredging would only take place alongside and
downstream of the commercial jetties, thus avoiding disturbance of any of the sediments in
the upper part of the channel (thereby excluding the channel from dredging between Stations
1-4).
During the course of consultations with local fishermen, concerns were raised regarding
contamination of the sediments by the former operation of the untreated sewage outfall at
Finisklin, prior to the commissioning of the new waste water treatment works. The analysis
of the sediments shows that the organic content within all the samples, including those within
the port, is low. Consultation has been held with the Marine Institute who have confirmed
14-13
that the history of the site has been taken into consideration in setting the parameters for
testing. The results of these tests show that the suspension of sediments in the navigation
channel during the dredging process pose no chemical risk to the sensitive habitats within
the harbour nor the habitats at the proposed dump site. The physical impacts of the
sediments (e.g. smothering, increased turbidity) are considered in more detail in Chapter 6.
The results of the radiological analysis undertaken by the Radiological Protection Institute of
Ireland have confirmed that the sediments to be dredged pose no radiological risk.
The Marine Institute have confirmed that the sediment quality of the material to be dredged is
clean and suitable for disposal in Irish Waters (pers comm. Margot Cronin, Marine Institute
15 February 2010) and a separate dumping at sea licence will be applied for in parallel to the
planning/foreshore consents.
14.3.2 Dredged Sediments Properties Conclusions
Physical, chemical and radiological testing of the sediments within the navigation channel at
Sligo Harbour have been undertaken to determine whether these sediments are suitable for
dredging and dumping at sea. The results of the tests have shown that the sediments within
the dredging area are clean and free from contamination and will not pose any significant
impact on the sensitive habitats and species within both the dredging area and the proposed
offshore dump site.
Mitigation measures to reduce the amount of sediment placed into suspension during
dredging activities and thus limit the physical impact of the dredging activity within Sligo
Harbour are described in Chapter 4.0 Project Description and Chapter 11 Coastal
Processes.
14.4
Potential Impacts during Dredging
14.4.1 Short term increase in Suspended Sediment and Turbidity
The scale and extent of increases to suspended sediment during dredging operations are
described in detail in section 11.1.4 of Chapter 11 “Coastal Processes”. The modelled
results show that during dredging, the suspended sediment concentration rapidly increases
during slack water as the tide turns, but quickly returns back to the background values once
current speeds pick up again. Although the concentration reaches relatively high values, the
periods during which this occurs are very short in duration. The period during which
suspended sediment concentrations are elevated within any of the sensitive areas within the
harbour will last on average up to two hours, with the highest peak values lasting 15-30
minutes. The period between peaks, where concentrations return to baseline levels, will be
much longer, around 10 hours per tide.
14-14
The areas which experience the greatest peaks in suspended sediments are along the
northern shore of the harbour, the eastern shore of Coney Island and the area south of the
training wall.
Environmental Quality Standards (EQS) for certain pollutants in surface waters in Ireland are
outlined in the European Communities Environmental Objectives (Surface Waters)
Regulations, 2009 (S.I. No. 272 of 2009). The purpose of the EQS is to limit the quantity of
certain pollutants in surface waters in order to achieve the environmental objectives
established for waters by Directive 2000/60/EC, the Water Framework Directive (WFD).
However, an EQS is not established in these Regulations for suspended sediments. Article 5
of the Shellfish Directive (2006/113/EC) and section 6 of the Quality of Shellfish Waters
Regulations, 2006 (S.I. No. 268 of 2006) require the development of Pollution Reduction
Plans (PRPs) for designated shellfish areas in order to improve water quality in designated
shellfish areas and to achieve compliance with water quality parameter values outlined in
Annex I of the Directive and Schedules 2 and 4 of the Regulations. Imperative (I) values
must be fully achieved while it must be endeavoured to achieve guideline values (G).
There are no guideline values for suspended solids established in the Regulations, however
the mandatory value states:
“A discharge affecting shellfish waters must not cause the suspended solid content of the
waters to exceed the content in unaffected waters by more than 30%”
This measure can be considered conservative as it is designed to protect shellfish life and
growth and shellfish are sensitive to suspended solids as shellfish species are generally
bottom dwellers and/or filter feeders.
In order to be compliant with the shellfish mandatory value for suspended solids, suspended
solid concentrations much not be raised more than 30% above background concentration.
This standard is expressed as a 75-percentile, i.e. the value below which 75 percent of the
observations may be found.
Available suspended solid monitoring results from the Marine Institute water quality
monitoring station in Sligo Harbour (listed in Table 11.1 in Chapter 11) demonstrate that the
background levels measured at the monitoring station in Sligo Harbour have varied between
<2mg/l and 72mg/l between 2009 and 2011.
If we eliminate the highest 25% of readings, the 75th percentile level for suspended
sediments is between 12.0-25.6mg/l. Although there will be some very short term peaks in
suspended sediments, the modelling in Chapter 11 shows that concentrations will return to
background levels within a short period of time. The predicted average increase in
suspended sediments at the Marine Institute water quality sampling point is 10mg/l, therefore
proposed dredging works will not cause water quality issues in this area to an extent that
would constitute a non-compliance with the Shellfish Regulations.
14-15
The localised nature of the impact and the short duration of dredging activity mean that the
impact to water quality within Sligo Harbour is anticipated to be of minor adverse impact
over a short term period.
14.4.1.1
Mitigation and Residual Impact
Solids will be monitored during the dredging. If it is deemed that these concentrations are
rising above predicted concentrations, then a decision can be made to slow the dredging rate
in order to reduce the level of solids escapement.
The short term temporary suspension of solids during dredging will not have any significant
impact on the receiving area in terms of meeting the requirements of the EC Bathing Waters
Directive , the EC Shellfish Waters Directive or the EC Water Framework Directive.
14.4.2 Potential for the Spread of Contaminated Dredged Material
As described above in 14.3.1.2 “Sediment Quality Results”, the material to be dredged has
been extensively tested for levels of contamination by a certified laboratory under the
supervision of the Marine Institute. All of the sediment samples within the area to be
dredged have contaminant levels beneath the lower level2.
There are therefore no significant impacts to water quality arising from contaminated
dredged material anticipated for this scheme. No mitigation is therefore necessary.
14.4.3 Potential for impacts to Dissolved Oxygen and Nutrients
Dissolved oxygen concentrations may decrease in the vicinity of the dredge during the
dredging operation due to increased levels of suspended sediment. Levels of organic
material within the sediment to be dredged have been measured as low, which lowers the
risk of DO reduction. There may also be low levels of nutrients within the silty surface layer
of sediment which may be resuspended and therefore may enter the water column. Again
these events will be short-lived and mostly confined to the dredge area. Any changes outside
of the dredge area will be minimal and transient, returning to background levels following
completion of the dredge. The impact to water quality in terms of dissolved oxygen levels
and nutrient levels is anticipated to be of minor adverse impact over a short term period.
The dredging will not have any significant impact on the receiving area in terms of meeting
the requirements of the EC Bathing Waters Directive, the EC Shellfish Waters Directive or
the EC Water Framework Directive.
14.4.4 Potential for impact on Water Quality in the wider Sligo Bay area
As described in Chapter 11 “Coastal Processes” there will be temporary short term increases
in suspended sediment within the harbour during the dredging period. Due to the enclosed
nature of Sligo Harbour, which only drains into Sligo Bay through the channels to the north
2
The lower level (Level 1) defines a concentration (i.e. guidance value) of a contaminant in sediment
below which biological effects would not be anticipated (Cronin et al, 2006).
14-16
and south of Coney Island, these increases will be almost entirely confined to the harbour
area. Some areas, near the drainage channels will experience very slight increases in
suspended sediment of less than 5mg/l during the dredging. The potential impact on water
quality in the wider Sligo Bay area is therefore regarded to be insignificant and there will be
no impact on the designated bathing waters at Rosses Point due to the dredging project.
14.4.5 Accidental Spillages during Dredging Operations
During dredging, there is the potential for accidental spillages from the dredger itself, such as
fuel oil. However, it will be a requirement of the contract documents that operational
safeguards in regards to best environmental practice will be in place by the dredging
operator who must also demonstrate specific experience in working in environmentally
sensitive areas. With all necessary safeguards in place, the anticipated potential impact will
be of minor adverse significance.
14.4.5.1
Accidental Spillages - Mitigation Measures and Residual Impact
The port of Sligo will already have an oil spill contingency plan in place as required by the
Sea Pollution Act 1999. The Irish Coast Guard is the lead authority designated by the
Minister of Transport to approve plans and levels of response and resources required to
comply with the requirements of this Act. The appointed dredging contractor will be required
to prepare and submit an Environmental Management Plan (EMP) which will be implemented
to reduce or eliminate, where possible, the likelihood of any impact to the marine
environment during construction. The EMP must include the procedures which will be put in
place to deal with any accidental spillages. With these measures in place, the residual
impact of accidental spillages is anticipated as of negligible significance.
14-17
14-18
Summary of Impacts and Mitigation Measures
15.0 SUMMARY OF IMPACTS AND MITIGATION MEASURES
15.1
INTRODUCTION
Chapters 5.0 to 14.0 of this Environmental Appraisal Report assess the likely significant
impacts arising from the proposed coastal protection scheme. This section summarises the
impacts identified and the suggested mitigation, where necessary, to reduce or eliminate the
negative impacts.
Table 15.1 provides a summary of the potential impacts identified within the Environmental
Report and identifies the mitigation measures outlined to reduce or eliminate these impacts.
The timescale during which the mitigation is appropriate is also outlined, as well as who will
be responsible for implementing the mitigation.
15.2
TECHNICAL DIFFICULTIES
The studies involved in assessing the environmental impact of the project have been
undertaken throughout a period spanning more than two years, during which extensive
baseline surveying was carried out, during the appropriate season. As a result, there were
no technical difficulties encountered during the preparation of this Environmental Appraisal
Report.
15-1
Potential Impact
Proposed Mitigation Measure
Who will be
responsible for
implementation
n/a
n/a
Not
Significant
Design & During
Dredging
These measures
will be
implemented by
the contractor
Not
significant
n/a
n/a
Not
significant
Residual
Impact
BIRDS
Physical Disturbance
The physical act of dredging by the dredging vessel and its crew has
the potential to cause some temporary disturbance to waterbird
populations in Sligo Harbour.
15-2
Removal of sediments from the estuary along the shipping
channel.
This will result in the loss of some sub-tidal and intertidal habitat and
has the potential to impact on the stability of the training walls along
the shipping channel, which are an important roost site for waterbirds.
Removal of sediments from the estuary along the shipping
channel.
This will impact directly on the benthic environment and has the
potential to negatively impact on the infaunal macrobenthos which acts
as important food source for waterbird species in the estuary.
Bird species in the harbour are already subject to disturbance from
recreation, transport (shipping movements in the harbour and low
flying aircraft in the area of Sligo Airport) and other activities and
appear to be habituated to current levels of disturbance.
Disturbance to waterbird species as a result of the proposed
dredging activities (either alone or in combination with existing
disturbance levels) will result in an imperceptible impact. It is
extremely unlikely to have a significant negative effect on
waterbirds within Sligo Harbour/Cummeen Strand, even in the
short term therefore no mitigation is necessary.
No mitigation measures are possible in terms of habitat loss, aside
from ensuring that dredging is kept to minimum required footprint.
The proposed dredging will leave adequate distance from the
training walls so that the walls are not disturbed.
No mitigation necessary.
Areas being dredged are demonstrated in Appraisal Report as not
being the principal feeding areas for cSAC/SPA feature bird
species
Time scale,
relative to
project, of
mitigation
implementation
Table 15.1 Summary of Potential Impacts and Proposed Mitigation Measures
Deposition of sediments on mudflats and sandflats
The dispersion and settlement of sediment released during the
dredging works has the potential to cause impacts directly on the
intertidal environment (habitats and fauna) within Sligo Harbour and
also may have associated indirect impacts on waterbird species within
the SPA.
No mitigation necessary.
Areas being dredged are demonstrated in Appraisal Report as not
being the principal feeding areas for cSAC/SPA feature bird
species.
n/a
n/a
Not
significant
No mitigation measures are possible, aside from ensuring that
dredging is kept to minimum required footprint.
During Dredging
These measures
will be
implemented by
the contractor
Not
significant
No mitigation measures are possible.
Sensitive habitats may be monitored during dredging to confirm
that sedimentation is not exceeding predicted levels.
n/a
n/a
Not
significant
Who will be
responsible for
implementation
Residual
Impact
Potential Impact
Time scale,
relative to
project, of
mitigation
implementation
INTERTIDAL FLORA AND FAUNA (DREDGING AREA)
15-3
The removal of estuarine sediments
There will be a loss of benthic habitat along the navigational channel
as a result of sediment removal. Along the channel where dredging
occurs, removal of all surface sediment and associated fauna will
occur over a relatively short time frame. (The dredging will extend
across an area of up to 271,910m², which is 0.56% of the SAC area
(48,541,373m²).
Deposition of sediments on mudflats and sandflats
During and after the proposed dredging operations, sediment is
deposited along the sides of the navigation channel and along the
north shore of the harbour area. Some of the deposition is temporary
and will be resuspended and transported away in subsequent tidal
cycles, however a small amount of residual sedimentation will remain
following completion of dredging operations.
Who will be
responsible for
implementation
Residual
Impact
During Dredging
These measures
will be
implemented by
the contractor
Not
significant
Not
significant
SUBTIDAL FLORA AND FAUNA (DREDGING AREA)
15-4
The removal of benthic habitat
There will be a loss of benthic habitat along the navigation channel as
a result of sediment removal. Along the channel where dredging
occurs, removal of all surface sediment and associated fauna will
occur over a relatively short time frame. (The dredging will extend
across an area of up to 271,910m², which is 0.56% of the SAC area
(48,541,373m²).
No mitigation measures are possible, aside from ensuring that
dredging is kept to minimum required footprint.
Elevation of suspended sediment levels in the water column
Large quantities of suspended sediment in the water column can be
detrimental to fish, bivalves and other aquatic organisms due to
clogging of the gills and impairment of proper respiratory and excretory
functioning and feeding activities.
No mitigation is necessary as suspended sediment levels during
dredging have been modelled as being well within the tolerances
supported by the species in the harbour. Suspended sediment
levels at vulnerable locations will be monitored during dredging to
ensure that they are within the modelled parameters.
During Dredging
These measures
will be
implemented by
the contractor
No mitigation measures are possible. Post-dumping monitoring is
recommended (see fisheries and aquaculture section below)
n/a
n/a
Not
Significant
During Dredging
These measures
will be
implemented by
the contractor
Not
significant
Potential Impact
Time scale,
relative to
project, of
mitigation
implementation
SUBTIDAL FLORA AND FAUNA (PROPOSED DUMP SITE)
Elevation of suspended sediment levels in the water column
Suspended solids in the dumpsite area will be temporarily increased
during the dumping phase. However, mobile species will have the
opportunity to move away from areas affected by the dredge plume.
The sediments will dilute and disperse rapidly as they settle through
the water column to insignificant levels above background.
No mitigation measures are necessary, however a monitoring
programme is recommended to ensure that modelled levels are
not exceeded (see fisheries and aquaculture section below)
The settling of dumped sediments on the sea bed
The majority of the dumped sediments will be deposited and will
remain within 2km of the dumpsite. Benthic species within this area
which are unable to burrow through the dumped sediment may be
smothered. Given the relatively small area of impact relative to the
surrounding habitats, there should be no significant negative impact on
the bottom communities from Donegal Bay
Who will be
responsible for
implementation
During Dredging
and Dumping
Operations
These measures
will be
implemented by
the contractor
Residual
Impact
MARINE MAMMALS
A trained and experienced Marine Mammal Observer (MMO)
should be put in place during dredging and dumping operations.
The MMO will scan the surrounding area to ensure no marine
mammals are in a pre-determined exclusion zone in the 30 minute
period prior to commencing dredging operations.
15-5
Collision Risk
There is a small possibility that collision impacts causing injury or
death may be suffered by individual grey or harbour seals entering the
works zone
Risk of hearing or disturbance/displacement as a result of noise
Underwater works can generate noise at levels harmful to cetaceans
and pinnipeds.
Potential Impact
Time scale,
relative to
project, of
mitigation
implementation
Once operations have begun operations should cease temporarily
if a cetacean or seal is observed swimming in the immediate
(<50m) area of industrial activity and work can be resumed once
the animal(s) have moved away.
Dumping of material at sea should not take place if a cetacean or
seal is within 50m of the vessel.
Any approach by marine mammals into the immediate (<50 m)
works area should be reported to the National Parks and Wildlife
Service.
If feasible, the MMO will take photographs of dorsal fins of
Bottlenose dolphins encountered, for the purpose of contributing to
the Irish Whale and Dolphin Group (IWDG) catalogue of images
for photo-identification.
The MMO will keep a record of the monitoring using an MMO form
“Location and Effort (Coastal Works)” available from the National
Parks & Wildlife Service (NPWS) and submit to the NPWS on
completion of the works.
Not
Significant
Elevation of suspended sediment levels in the water column at
Dredging Site and Dumping Site
Sediment plumes may present a small level of habitat disturbance to
local seals foraging in the area. Visibility may be temporarily reduced.
The areas which will be influenced by the dredging and dumping
plumes are not known as important feeding areas for pinnipeds or
cetaceans.
Water Quality Monitoring
(See fisheries and aquaculture section below)
Who will be
responsible for
implementation
Residual
Impact
During Dredging
and Dumping
Operations
These measures
will be
implemented by
the contractor
Not
significant
During Dredging
These measures
will be
implemented by
the contractor
Not
Significant
Potential Impact
Time scale,
relative to
project, of
mitigation
implementation
FISHERIES AND AQUACULTURE
15-6
Impacts of increased suspended sediment and deposition of
suspended sediments on aquaculture
Sediment deposition at licensed aquaculture sites in Sligo Harbour is
predicted to be very low (<2 mm) during dredging of both the upper
and lower channel, while completion of the works will be lower still (0-1
mm). Manila clam and pacific oysters under cultivation at these sites
are buried naturally in the substrate and will be unaffected by these
negligible levels of sediment deposition.
Turbidity is recorded in National Turbidity Units (NTU) and may be
used as an indicator of the concentration of Suspended Solids
(SS). A programme of calibration linking Turbidity (NTU) and SS
(mg/l) should be carried out using solutions of known SS
concentration made up from samples of the sediments to be
excavated.
Triggers levels should be established which, if exceeded, would
lead to immediate suspension of dredging until levels have
recovered.
Impacts of increased suspended sediment on salmonids
Suspended sediment concentrations in the lower 0.5m of water
column are predicted to remain relatively low throughout dredging
operations. Adult salmonids are most likely to move upstream via the
navigation channel where the mean concentration be slightly higher
but will remain within the Fish Directive recommended limit of 25 mg/l
for salmonid waters. Moreover, suspended sediment concentrations
are likely to be lower in the upper layers of the water column which
salmon more commonly utilise when swimming through estuarine and
coastal waters.
A monitoring programme is recommended to take regular
measurements of dissolved oxygen (DO) and turbidity in Sligo
Harbour during dredging operations. There parameters should be
recorded in the immediate area of dredging and at key locations in
the navigation channel and at shellfish aquaculture sites.
Who will be
responsible for
implementation
Residual
Impact
During Dumping
These measures
will be
implemented by
the licensing
authority
Not
significant
During Dumping
These measures
will be
implemented by
the contractor
Not
Significant
Impacts of increased suspended sediment on eel and lamprey
Eel and lamprey migrating through estuarine environments may
encounter higher than background suspended sediment loads.
Projected levels of suspended sediment are within recommended
guidelines and will not have an adverse effect the upstream and
downstream migrations of eels and lamprey
Potential Impact
Time scale,
relative to
project, of
mitigation
implementation
Impact of dredging on sea angling
Sediment deposition and suspended sediment concentrations are
predicted to be negligible at recognised sea angling locations and
outside of Sligo Harbour where all boat-based fishing activity takes
place
15-7
The impacted seafloor will be re-colonised from the surrounding faunal
community and will integrate as part of the overall habitat. Recolonisation should take place within a relatively short period of time
(12-18 months).
Impact of offshore disposal on other fishery activity
Fish may have reduced feeding opportunities in the area of the
dumpsite due to short term habitat loss on the seabed and reduced
Closure of site to fishing
The dumpsite and surrounding area to a radius of 1km should be
closed to commercial fishing activity during dumping operations.
This will be to avoid any damage to or loss of fishing gear.
A second monitoring programme is recommended for the
dumpsite. This exercise would also take regular measurements of
dissolved oxygen (DO) and turbidity at the site and surrounding
area during dumping operations.
Triggers levels should be established for each parameter with
readings to be taken along set transects emanating from the edge
of the site.
Impact of offshore disposal on crab fishery
Many sessile and some mobile species covered by the dumped
material will be lost, notably where the material settles deepest after
each dumping event. This may include crab although there is
evidence to show that smothering is unlikely to cause mortality in
crabs, which are able to escape from under silt and migrate away from
an area where dumping is taking place.
productivity. However, fish in the vicinity of dredge disposal operations
will avoid areas affected by the dredge plume.
ROV monitoring of seabed
ROV equipment should be deployed following completion of
operations to verify settlement of dumped materials in the
designated area.
15-8
Crustacean Monitoring Programme
A crustacean monitoring programme is recommended for the
dumpsite to determine any impact on shellfish stocks and the
recovery period – this should be based on the crab stock. It is
suggested that individual fishermen should be contracted to fish at
pre-determined locations in the region of the dumping site.
Verification of fishing activity and catch would be required. The
programme should include baseline monitoring of the site prior to
dumping and resumed after dumping to examine recovery of the
site.
Who will be
responsible for
implementation
Residual
Impact
During Dumping
and on completion
of Dumping
These measures
will be
implemented by
the applicant
under the
supervision of
the relevant
licensing
authority
Not
Significant
During Dredging
and on completion
of Dumping
These measures
will be
implemented by
the applicant
under the
supervision of
the relevant
licensing
authority
Not
Significant
Potential Impact
Time scale,
relative to
project, of
mitigation
implementation
AIR AND CLIMATE
Responsible Person
It is recommended that the applicant and contractor should appoint
or delegate a responsible person who will be present on site and
who will be willing to answer and act upon queries from the local
public.
It is recommended that local residents are duly notified of intended
works in close proximity to their residences, particularly during
night time hours as this will help to alleviate tensions and reduce
potential for noise complaint related to the dredging activity.
Dredging noise impact on local residents
Dredging will occur along the northern shore of Sligo Harbour, within
the navigation channel extending from Oyster Island to the Deepwater
and Barytes jetties. There are a small number of residential units
located along this length of the coast, situated at varying distances
from the shore, the most proximate circa 150m from dredging activity
at Ballincar. Dredging operations will occur on a 24 hour basis, but
only for a short period (1-2 hours) every 12 hours.
Monitoring
Occasional measurement of noise levels generated using a Type 2
or better sound level meter should be conducted to check on the
continuing impact of the works.
Who will be
responsible for
implementation
No mitigation measures are necessary
n/a
n/a
Not
Significant
n/a
n/a
Not
Significant
n/a
n/a
Not
Significant
No mitigation measures are possible
n/a
n/a
Not
Significant
Residual
Impact
MATERIAL ASSETS
Impact of Traffic
Dredging works has the potential to create additional traffic to the port
area. However, the increase in vehicle numbers travelling to the port
is not significant.
Potential Impact
Time scale,
relative to
project, of
mitigation
implementation
GEOLOGY
15-9
Potential impacts to Groundwater Resource
The proposed dredging will only remove sediments from the bed of the
navigation channel. No removal of bedrock is envisaged with this
scheme, therefore there is no risk of creating a new pathway for saline
intrusion to occur. There is no risk of increasing nutrient loadings as a
result of the proposed dredging.
HYDRODYNAMIC MODELLING
Impact of Dredging on Water Levels
The proposed dredging will not result in any increase in water level at
high tide, therefore the proposed dredging of the channel will not
cause any increase in the risk of flooding in Sligo from high spring
tides. At extreme low spring tides there will be a slightly larger drying
area for a maximum of 2 hours.
Potential Impact to seabed at dumpsite due to physical or
chemical properties of dredged spoil
Both physical and chemical testing has been undertaken for the
dredged sediment and the receiving sediments at the dump site. The
physical properties of the sediments at the dump site are similar to the
dredged material, and the dredged material is free from contamination.
Who will be
responsible for
implementation
Residual
Impact
15-10
No mitigation measures are possible
n/a
n/a
Not
Significant
Impact of Dredging on sedimentation in Sligo Harbour
During dredging, small areas of the harbour may temporarily
experience sedimentation of up to 70mm for short periods. The
maximum final deposition depth of dredged sediments in Sligo
Harbour on completion of dredging is less than 1mm in the majority of
the harbour area. The deposition exceeds 25mm only in a small
number of very localised sites, mainly around the training wall and
northern shore of the harbour. Two very small areas (less than 300m²)
will experience final sediment deposition depths in excess of 25mm.
n/a
n/a
Not
Significant
During Dredging
Operations
These measures
will be
implemented by
the contractor
Not
significant
Impact of Dredging on suspended sediment levels in Sligo
Harbour
Modelling shows that significant elevations in suspended sediment
within Sligo Harbour caused by the dredging only occur in the
immediate vicinity of where the dredger is working, within the confines
of the navigation channel.
The areas in which sensitive habitats have been identified, at Cartron
Marsh, southern Cummeen Strand and at the various aquaculture
sites will experience very short term increases in suspended sediment
concentrations in the lowest 0.5m of the water column, mainly during
slack water at spring tides. However, these increases are of short
term duration and are well within the tolerance levels of the sensitive
flora and fauna within the harbour.
(See fisheries and aquaculture section above)
Impact of Dredging on Tidal Current Speeds
The difference in the mean tidal current velocities is generally very
small (less than 0.1 m/s) and the changes are restricted to the area
around the channel and the northern section of the harbour area.
Peak velocity increases of up to 0.4m/s may be experienced in
localised areas north of the navigation channel.
Potential Impact
Time scale,
relative to
project, of
mitigation
implementation
Impact of dumping on suspended sediment levels at Offshore
Dump Site
Modelling shows that during dumping operations there will be
temporary increases in suspended sediment levels within the water
column as the dumped materials settle out.
Residual
Impact
During Dumping
Operations
These measures
will be
implemented by
the contractor
Not
significant
On completion of
Dumping
These measures
will be
implemented by
the applicant
under the
supervision of
the relevant
licensing
authority
Not
Significant
During Dredging
These measures
will be
implemented by
the applicant
under the
supervision of
the relevant
licensing
authority
Not
Significant
The increases are shown in the models to be temporary in nature and
not significant however it is recommended that water quality
monitoring is undertaken during dumping operations to confirm that
the modelling predictions are accurate.
15-11
Impact of dumping by depositing sediments on sea bed at
Offshore Dump Site
The final settlement model shows that the dumped sediment will
accumulate on the seabed close to the dump site. An area extending
approximately 2km to the east and south of the dumpsite will
experience deposition in excess of 20mm. Within this, an area
measuring approximately 0.5km² will experience deposition depths in
excess of 130mm.
ROV monitoring of seabed
ROV equipment should be deployed following completion of
operations to verify settlement of dumped materials in the
designated area.
No mitigation is possible to reduce the extent of the area experiencing
final settlement of the dumped sediments, however recolonisation and
recovery should occur within a year.
CULTURAL HERITAGE
Physical impact of dredging within the navigation channel
Excavation has the potential to disturb previously unrecorded
archaeological artefacts.
Archaeological Monitoring
A competent maritime archaeologist should be retained for the
duration of the relevant works. In the event of archaeological
features or material being uncovered during dredging, it is crucial
that any machine work cease in the immediate area to allow the
archaeologist/s to inspect any such material.
If the presence of archaeologically significant material is
established, full archaeological recording of such material is
recommended.
Who will be
responsible for
implementation
Potential Impact
Time scale,
relative to
project, of
mitigation
implementation
Physical impact of dumping on the sea bed
Dumping has the potential to disturb previously
archaeological artefacts.
unrecorded
No mitigation measures necessary
Who will be
responsible for
implementation
n/a
n/a
Not
significant
During Dredging
These measures
will be
implemented by
the applicant
with the
assistance of the
Contractor
Not
Significant
Residual
Impact
Potential Impact
Time scale,
relative to
project, of
mitigation
implementation
HUMAN BEINGS
15-12
Impact of dredging operations on recreation activities in the
harbour
During the dredging operations, there may be some temporary minor
disruption to using leisure craft within the harbour, depending on the
time of year the dredging takes place.
Communication with stakeholder groups
Sligo County Council will establish a mechanism for liaison with
the local sailing clubs and recreational users of the harbour.
Harbour users will be informed of the programme of works
anticipated over the dredging period, e.g. by newspaper notices
and information boards at slipways and launching sites.
Of particular importance will be the requirement to coordinate with
local sailing organisations to ensure that dredging activities do not
pose a conflict with any scheduled major sailing events
Who will be
responsible for
implementation
Residual
Impact
During Dredging
Operations
These measures
will be
implemented by
the contractor
Not
significant
SEDIMENT AND WATER QUALITY
15-13
Temporary increases in Suspended Sediment and Turbidity
within Sligo Harbour in the context of:
x
EU Bathing waters directive
x
EU Shellfish waters directive
x
EU Water Framework Directive
During dredging operations, the suspended sediment concentration
rapidly increases during slack water as the tide turns, but quickly
returns back to the background values once current speeds pick up
again. Although the concentration reaches relatively high values, the
periods during which this occurs are very short in duration.
The changes to suspended sediment and turbidity have been
assessed to not have any significant impact to the sensitive species
and habitats within the harbour area, this will be verified by monitoring.
Potential for impacts to Dissolved Oxygen and Nutrients
Dissolved oxygen concentrations may decrease in the vicinity of the
dredge during the dredging operation due to increased levels of
suspended sediment. Levels of organic material within the sediment
to be dredged have been measured as low, which lowers the risk of
DO reduction. There may also be low levels of nutrients within the silty
surface layer of sediment which may be resuspended and therefore
may enter the water column. Again these events will be short-lived
and mostly confined to the dredge area. Any changes outside of the
dredge area will be minimal and transient, returning to background
levels following completion of the dredge.
Potential Impact
Time scale,
relative to
project, of
mitigation
implementation
Who will be
responsible for
implementation
Residual
Impact
15-14
n/a
n/a
Not
significant
Potential for impact on Water Quality in the wider Sligo Bay area
Due to the enclosed nature of Sligo Harbour, which only drains into
Sligo Bay through the channels to the north and south of Coney
Island, these increases will be almost entirely confined to the harbour
area. Some areas, near the drainage channels will experience very
slight increases in suspended sediment of less than 5mg/l during the
dredging. The potential impact on water quality in the wider Sligo Bay
area is therefore regarded to be insignificant and there will be no
impact on the designated bathing waters at Rosses Point due to the
dredging project.
n/a
n/a
Not
significant
During Dredging
Operations
These measures
will be
implemented by
the contractor
Not
significant
Impact of Accidental Spillages during Dredging Operations
Accidental pollution from dredging plant has the potential to degrade
habitats and bird feeding resources in the harbour.
The appointed dredging contractor will be required to prepare and
submit an Environmental Management Plan (EMP) which will be
implemented to reduce or eliminate, where possible, the likelihood
of any impact to the marine environment during construction.
The EMP must include the procedures which will be put in place to
deal with any accidental spillages. With these measures in place,
the residual impact of accidental spillages is anticipated as of
negligible significance.
Potential for the Spread of Contaminated Dredged Material
During dredging operations, if the material to be dredged contains
contaminants, these can be spread across the receiving area. The
sediments to be dredged at Sligo harbour have been chemically tested
and have been found to be free from contamination therefore there is
no risk of this impact occurring in this project.
Potential Impact
Time scale,
relative to
project, of
mitigation
implementation
Environmental Impact Statement
Table 15.2 Interactions
(see text below for brief description of the interactions)
Human Beings
Cultural Heritage
Geology &
Hydrogeology
Coastal
Processes
Material Assets
Air & Climate
Intertidal and
Underwater Flora
& Fauna
Birds
Birds
Intertidal and
Subtidal Flora
& Fauna
A
Air & Climate
B
None
Material
Assets
None
None
None
Coastal
Processes
C
E
None
None
Geology
None
None
None
None
None
Cultural
Heritage
None
None
None
None
None
None
Human Beings
None
None
G
H
I
None
None
Sediment and
Water Quality
D
F
None
None
J
K
None
A
L
Birds and intertidal/subtidal flora and fauna
Reductions in species abundance and diversity within the intertidal and subtidal
habitats within the harbour has the potential to impact Bird as there may be an
associated reduction in availability of prey or foraging areas. No significant impacts
are predicted to intertidal and subtidal flora and fauna. Mitigation in the form of
monitoring during dredging operations has been recommended in Table 15.1 to verify
that predicted suspended sediment concentrations are achieved. If agreed trigger
levels are exceeded, the dredging methodology can be altered to ensure that harmful
levels are not encountered.
15-15
B
Birds and air and climate
Birds have the potential to be disturbed by dredging noise. However the birds within
the harbour are already subject to disturbance by recreation and commercial vessel
movement within the harbour and are unlikely to be significantly impacted.
C
Birds and coastal processes
The dredging will allow water to drain out of the navigation channel more quickly during
the ebb tide. This will result in a lower low water level during extreme spring tides,
creating a larger drying area than before the channel was dredged for a period of
approximately two hours per affected tide (a few times per year). This impact cannot
be mitigated against but is not considered to be significant.
D
Birds and sediment and water quality
Increased levels of suspended sediments and turbidity have the potential to impact bird
feeding. Mitigation measures in the form of monitoring of suspended sediments to
ensure they are in accordance with the levels predicted in the model (which are not
significant) and do not exceed agreed trigger levels during dredging are recommended
in Table 15.1
E
Intertidal and underwater flora and fauna and coastal processes
Physical alterations to the channel as a result of dredging will have localised minor
adverse impacts on intertidal and subtidal flora and fauna due to alterations in current
speeds. No mitigation is possible, however the estuary is a dynamic environment and
the affected species are adapted to changes in current speeds.
F
Intertidal and Underwater Flora & Fauna and Sediment and Water Quality
Increased levels of suspended sediments and turbidity have the potential to impact
intertidal and subtidal species. Mitigation measures in the form of monitoring of
suspended sediments to ensure they are in accordance with the levels predicted in the
model (which are not significant) and do not exceed agreed trigger levels during
dredging are recommended in Table 15.1. Settlement of suspended sediments has
the potential to impact intertidal and subtidal habitats. Sensitive habitats may be
monitored during dredging to confirm that sedimentation is not exceeding predicted
levels.
G
Air and Climate and Human Beings
Noise from dredging operations has the potential to cause nuisance to residents of
nearby dwellings. Mitigation measures are recommended in Table 15.1.
H
Material Assets and and Human Beings
Increases in traffic generation associated with dredging have the potential to cause
nuisance to commuters. The traffic associated with the proposed scheme has been
assessed and found to be not significant.
I
Coastal Processes and Human Beings
Dredging activities have the potential to cause temporary disruption to recreational use
of the navigation channel. Mitigation measures are recommended in Table 15.1.
15-16
J
Coastal Processes and Sediment and Water Quality
Alterations to the coastal processes in a beach environment harbour have the potential
to alter the distribution of sediments within the harbour, such as causing accelerated
erosion or accumulation of sediments. The changes to current speeds around the
navigation channel associated with the dredging will have no impact on the coastal
processes within Sligo Harbour.
K
Geology and Sediment and Water Quality
Dumping the dredged sediments at an offshore dump site has the potential to
significantly alter the composition of the bed sediments, both in terms of physical
properties or if the sediment is chemically contaminated. The dredged sediments have
been tested and have a similar granulometry profile to the bed sediments at the dump
site. The sediments have also been chemically tested and have been found to be free
of contamination therefore no significant impacts are anticipated and recolonisation
and restoration of habitats on the seabed at the dump site will be able to occur
relatively quickly.
L
Human Beings and Sediment and Water Quality
Excessive levels of suspended sediments or contaminants caused by the dredged
sediments being brought into suspension during dredging operations have the potential
to impact recreation activities such as bathing, or commercial activities such as
aquaculture if safe thresholds are exceeded. Mitigation measures in the form of
monitoring confirm that suspended sediments are not exceeding predicted levels is
recommended in Table 15.1.
15-17
15.3
Conclusions
The Environmental Appraisal and Appropriate Assessment have examined in detail the
potential impacts of the proposed dredging scheme at Sligo Harbour on the sensitive habitats
within the receiving area.
Where possible, every effort has been made to eliminate adverse impacts at source, through
the dredging methodology or by site selection. Where the risk of adverse impact remains,
mitigation has been outlined to reduce the significance of the impact to a level which is
considered to be not significant.
The impact of the generation of suspended sediments and subsequent settlement of these
sediments out of suspension as a by-product of the dredging has been extensively modelled
and assessed. The location of the offshore dump site has been carefully chosen to reduce
the impact of its use by placing at a distance from shore which allows the impacts of the
sediments being dumped to be confined to a small footprint. Detailed hydrodynamic models
have been prepared for both the dredge area and dump site which have been calibrated
against field data collected specifically for this purpose.
Upon completion of dredging and dumping operations, no significant residual negative
impacts have been identified. Some areas within the dredging area and dump site will be
temporarily affected by settling out of suspended sediments but these areas will recover
rapidly.
Monitoring of suspended sediment levels at sensitive areas during dredging has been
recommended as a mitigation measure to protect local aquaculture interests in addition to
the sensitive SAC and SPA habitats and species.
Impacts on commercial fishing for crustaceans at the dump site through damage to stocks
either by mortality or, more likely, by evacuation of the area are expected to be confined to
the immediate locality; probably no more than 0.5km from the dump site. At the proposed
dump site a ROV survey to monitor seabed impact has been proposed.
Throughout the dredging programme it will be important to involve stakeholders, in particular
commercial fishermen, commercial shellfish producers sailing clubs and local residents.
It is recommended that ongoing communication occurs with representatives of the local crab
fishing industry to ensure that fishermen are kept adequately informed with regard to project
progress and information from monitoring as it becomes available.
Sligo County Council, having overall responsibility for Sligo Port, is confident that the
proposed dredging will generate major positive benefits to Sligo city and the wider North
West region by securing its viability as a working commercial port, safeguarding existing jobs
and potentially creating new jobs by attracting businesses requiring cargo transport, and
avoiding the need for future investment in road transportation infrastructure.
15-18
Sligo County Council – Sligo Harbour Dredging
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Southern California Bight. Aquatic Mammals, 21, 51-63.
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abundance of harbour porpoises Phocoena phocoena (L.), white-beaked dolphins
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in the waters around the British Isles. ICES Journal of Marine Science, 52, 55-66.
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G., Masset, N., Klotzer, V & P. Whooley (2009). A note on long-distance matches of
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abundance. Report on research carried out under the Irish Infrastructure Programme (PIP):
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Offshore Support Group (OSG) project 99/38. 61pp.
Ó Cadhla, O., Strong, D., O’Keeffe, C., Coleman, M., Cronin, M., Duck, C., Murray, T.,
Dower, P., Nairn, R., Murphy, P., Smiddy, P., Saich, C., Lyons, D. & Hiby, A.R. (2007).
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Environment, Heritage and Local Government, Dublin, Ireland. 50pp.
Ó Cadhla, O. & Strong, D. (2007). Grey seal moult population survey in the Republic of
Ireland, 2007. Report to the National Parks & Wildlife Service, Department of the
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22pp.
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and Sipunculida. Irish Naturalists’ Journal, 22: 385-387.
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and Sons. pp.385.
Pollock, C. M., Reid, J. B., Webb, A & Tasker, M. L. (1997). The distribution of seabirds
and cetaceans in the waters around Ireland. JNCC Report No. 267. JNCC, Peterborough.
167pp.
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Pollack, C. M., Mavor, R., Weir, C. R, Reid, A., White, R. W., Tasker, M. L., Webb, A. &
Reid, J. B. (2000). The distribution of seabirds and marine mammals in the Atlantic Frontier
nort and west of Scotland. JNCC, Peterborough. 92 pp.
Richardson, W. J., Greene, C.R., Malme, C. I. & Thompson, D. H. (1995). Marine
Mammals and Noise. Academic Press, London, 576pp.
Rogan, E., Penrose, R., Gassner, I., Mackey, M., & Clayton, P. (2001). Marine Mammal
Strandings: A collaborative study for the Irish Sea. Marine Institute/Wales INTERREG
Report No. 8, 53pp.
Roycroft, D., Cronin, M., Mackey, M., Ingram S.N. and Ó Cadhla, O. (2007). Risk
Assessment for Marine Mammal and Seabird Populations in South-Western Irish Waters
(R.A.M.S.S.I.) Published by: Higher Education Authority - An tÚdarás um Ard-Oideacha ,
198 pp.
Selzer, L.A. & P.M. Payne. 1988. The distribution of white-sided dolphin (Lagenorhynchus
acutus) and common dolphins (Delphinus delphis) vs. environmental features of the
continental shelf of the north eastern United States. Marine Mammal Science 4(2):141-153
Shelton, R.G.J., (1973). Some effects of dumping, solid wastes on marine life and fisheries.
In: North Sea Science (ed. E.D. Goldberg) pp 415-436. London: The MIT Press
Summers, C.F., Warner, P.J., Nairn, R.G.W., Curry, M.G. & Flynn, J. (1980). An
assessment of the status of the common seal Phoca vitulina vitulina in Ireland. Biological
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thresholds of a harbour seal. In: Kastelein RA, Thomas JA, Nachtigall PE (eds) Sensory
systems of aquatic mammals. De Spil Publ, Woerden, Netherlands, p 81-93
Thompsen, F., McCully, S., Wood, D., Pace, F. & White, P. (2009). A generic investigation
into noise profiles of marine dredging in relation to the acoustic sensitivity of the marine
fauna in UK waters with particular emphasis on aggregate dredging. Phase 1 Scoping and
review of key issues. CEFAS contract report C3312. MEPF Ref No. MEPF/08/921
Thompson, P. M. & Miller, D. (1990). Summer foraging activity and movements of radiotagged common seals in the Moray Firth Scotland. Journal of Applied Ecology, 27, 492-501.
Thorson, G., 1957. Bottom communities (sublittoral or shallow shelf). Memoirs of the
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Tyler, P.A. and S.E. Shackley. (1980). The benthic ecology of linear sand banks: a
modified Spisula sub community. In: Industrial embayments and their environmental
problems. A case study of Swansea Bay. Ed. M.B. Collins. Pergamon Press. Oxford
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Van Parjis, S.M., Thompson, P.M., Tollit, D.J. & Mackay, A. (1997). Distribution and
activity of male harbour seals during the mating season. Animal Behaviour 54, 1, 35-43.
Van Parijs, S.M., Janik V.M. & Thompson, P.M. (2000). Display area size, tenure length
and site fidelity in the aquatically mating male harbour seal. Canadian Journal of Zoology,
78, 2209 - 2217.
Van der Heul, K., Verboom, Triesscheijn & Jennings (2006).The influence of underwater
data transmission sounds on the displacement behaviour of captive harbour seals (Phoca
vitulina).Marine Environmental Research, 61, 19–39.
Vincent, M.A., Atkins, S.M., Lumb, C.M., Golding, N., Lieberknecht, L.M. & M. Webster.
2004. marine nature conservation and sustainable development – the Irish Sea Pilot. Report
to Defra by the Joint Nature Conservation Committee, Peterborough.
Wilber, D.H. , G.L. Ray, D.G. Clarke andR.J. Diaz (2008). Responses of Benthic Infauna
to Large-Scale Sediment Disturbance in Corpus Christi Bay, Texas. Journal of Experimental
Marine Biology and Ecology, Volume 365, Issue 1, 20 October 2008, Pages 13–22
Gibson AM (1933) Construction and operation of a tidal model of the Severn Estuary.
London, HMSO.
MEMG (2003). Group Co-ordinating Sea Disposal Monitoring. Final Report of the Dredging
and Dredged Material Disposal Monitoring Task Team. Sci. Ser., Aquat. Environ. Monit.
Rep., CEFAS, Lowestoft, (55): 52pp.
Meredith, D. & Fahy, E. (2005). The status of the inshore component of the northern brown
crab cancer pagurus fishery, assessed from a time series of LPUE constructed from
historical sources. Irish Fisheries Bulletin No 23. 14pp.
Newcombe C.P. & MacDonald D.D. (1991). Effects of Suspended Sediments on Aquatic
Ecosystems. North American Journal of Fisheries Management, 11, 72-82.
Simenstad C.A. (1988). Effects of Dredging on Anadromous Pacific Coast Fishes.
Summary and Conclusions from Workshop and Working Group Discussions.
Simenstad C.A. & Nightingale B. (2001). Dredging Activities: Marine Issues. White Paper.
Research project T1803, Task 35. Washington State Transportation Centre.
Tully O, Robinson M, O'Keefe E, Cosgrove R, Doyle O and Lehane B, (2006). The
Brown Crab (Cancer pagurus L.) Fishery: Analysis of the resource in 2004 - 2005. Fisheries
Resource Series, Bord Iascaigh Mhara (Irish Sea Fisheries Board), Dun Laoghaire, Ireland
Vol. 4, 2006, 48pp.
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CHAPTER 8 AIR AND CLIMATE
BS5228 (2009), “Noise and Vibration Control on Construction and Open Sites”.
DEFRA (2005) “Noise Database for Prediction of Noise on Construction and Open Sites
Met Eireann (2011) Wind over Ireland http://www.met.ie/climate-ireland/wind.asp accessed
06/06/11
Met Eireann (2011) Rainfall http://www.met.ie/climate-ireland/rainfall.asp accessed 06/06/11
Met Eireann (2011) Air Temperature
temperature.asp accessed 06/06/11
http://www.met.ie/climate-ireland/surface-
Met Eireann (2011) The Marine Unit http://www.met.ie/marine/marine_climatology.asp
accessed 06/06/11
CHAPTER 9 MATERIAL ASSETS
NRA (2007) “Traffic and Transport Assessment Guidelines”
Sligo County Council (2005) “Sligo County Development Plan 2005-2011”
WFD Ireland (2009) “Western River Basin District - River Basin Management Plan”
CHAPTER 10 GEOLOGY AND SOILS
BS 5930 (1999) “Code of Practice for Site Investigation”
BS 1377 (1990), “Method of Tests for Soil for Civil Engineering Purposes, in situ Tests”.
Cronin, M., McGovern, E., McMahon, T., & Boelens, R. (2006) “Guidelines for the
assessment of dredge material for disposal in Irish Waters” (Marine Insitute/DCMNR)
Environmental Protection Agency (2010) “Dumping at Sea Permit - Application Guidance
Note”
GSI and Marine Insitute(2011) “Donegal Bay – Shaded Relief” (InfoMar Project)
http://www.infomar.ie/surveying/Bays/Donegalv1.php accessed 01/10/10
Macdermott, C.V., Long, C.B. and Harney, S.J. (1996) “Geology of Sligo-Leitrim“
Geological Survey of Ireland
B-12
CHAPTER 12 CULTURAL HERITAGE
Bennett, Isabel (ed.) (various dates.) Excavations Bulletin: summary accounts of
archaeological excavations in Ireland, (Bray, Wordwell),
Brady, Karl, (no date) Shipwreck inventory of Ireland. Louth, Meath, Dublin and Wicklow
(Dublin, Stationary Office
Jacobsthal, Paul, (1938): An Iberian Bronze Found at Sligo, Journal of the Royal Society of
Antiquaries of Ireland , 8 (1938): 51-54.
Kerrigan, Paul, (1975) Castles and fortifications in Ireland 1485-1945 (Collins Press, Cork).
Robinson, Auriel, (2010) ‘Discovering the maritime archaeological heritage of Sligo
Harbour and environs’, unpublished report submitted to the Heritage Council in 2010, grant
reference R00697.
Went, A. J., (1963) ‘Historical notes on the oyster fisheries of Ireland’, Proceedings of the
Royal Irish Academy 62 (1961-63): 195-223
CHAPTER 13
HUMAN BEINGS
CSO
Ireland
(2011)
“Census
Of
Population
2011
Preliminary
http://www.cso.ie/census/2011_preliminaryreport.htm accessed 05/08/11
Results”
CSO Ireland (2007) “Census 2006” Central Statistics Office, Ireland
CSO Ireland (2007) “Census 2006, Volume 7 - Principal Economic Status and Industries”
Central Statistics Office, Ireland.
CSO Ireland (2007) “Census 2006, Theme 13 - 1 : Persons at work or unemployed by sex
and occupation, 2006” Central Statistics Office, Ireland
CSO Ireland (2007) “Census 2006, SAPS - Small Area Population Statistics” Central
Statistics Office, Ireland
CSO Ireland (2007) “Census 2006 Volume 8, Occupations” Central Statistics Office, Ireland.
CSO Ireland (2012) Census 2011, Profile 2: Older & Younger Stationery Office, Dublin
EPA
(2011)
“Splash
–
http://www.bathingwater.ie/epa/home.htm
Annual
Water
Quality
Results”
Failte
Ireland
(2010)
“Tourism
Facts
2009-Angling”
http://www.failteireland.ie/FailteCorp/media/FailteIreland/documents/Research%20and%20S
tatistics/Tourism%20Facts/2009/Tourism_Facts_Angling_2009.pdf accessed 11/08/11
B-13
Failte
Ireland
(2010)
“Tourism
in
the
North
West,
2009”
http://www.failteireland.ie/FailteCorp/media/FailteIreland/documents/Research%20and%20S
tatistics/Tourism%20Facts/2009/rerevised-North-West-2009.pdf accessed 11/08/11
Failte Ireland (2005) “A New Strategy for Irish Angling Tourism”
Government of Ireland (2008) “Bathing Water Quality Regulations 2008”
Irish Tourist Industry Confederation (2011) “Tourism Opportunity – Driving Economic
Renewal”
O’Rourke, F. (2012) “Report on the Tourism Industry in the environs of Sligo City”
Pobal (2007) “Area Profile - Sligo county report” Trutz Haase Social & Economic
Consultants
Sligo County Council (2009) Sligo and Environs Development Plan 2010-2016
Sligo
Champion
(2011)
World
Sailing
event
for
Sligo
http://www.sligochampion.ie/sport/other-sports/world-sailing-event-for-sligo-2574735.html
accessed 18/07/2012
Sligo Yacht Club (2012) “About Us” http://www.sligoyachtclub.ie/index.php?id=2 accessed
25.06.2012
Western
People
(2011)
“Sligo
population
rises
http://www.westernpeople.ie/news/eysnqlgbgb/ accessed 08/08/2011
CHAPTER 13
by
over
7%”
SEDIMENT AND WATER QUALITY
Appleby, J.A., and Scarratt, D.J. (1989) Physical effects of suspended solids on marine
and estuarine fish and shellfish with special reference to ocean dumping: a literature review.
Can. Tech. Rep. Fish. Aquat. Sci. No. 1681.
Cronin, M, McGovern. E, McMahon,T. & Boelens, R. (2006) Guidelines for the
Assessment of Dredge Material for Disposal In Irish Waters
Water Framework Directive (2012) Full
(www.wfdireland.ie accessed 04/05/2012)
Report
for
Sligo
Harbour
Waterbody
Water Framework Directive (2012) Full Report for Garavoge Estuary Waterbody
Water Framework Directive (2012) Full Report for Sligo Bay Waterbody (www.wfdireland.ie
accessed 04/05/2012)
Water Framework Directive (2012) Full
B-14
Report
for
Sligo
Harbour
Waterbody
Water Framework Directive (2012) Full Report for Gill, Tributary of Garvogue Waterbody
Western River Basin District (2010) Western River Basin Management Plan (2009-2015)
EPA (2010) Water Quality in Ireland 2007-2009
EPA (2011) Water Framework Status Update - based on Monitoring Results 2007-2009
Sea Fisheries Protection Authority (2009) “Classified Bivalve Mollusc Production Areas in
Ireland” (2009)”.
EPA (2012) Rosses Point Beach Bathing Water Quality Status www.bathingwater.ie/epa/
accessed 06/06/2012
B-15
This Environmental Appraisal Report was prepared by:
RPS Consulting Engineers
Elmwood House
74 Boucher Road
Belfast
BT12 6RZ
Northern Ireland
Telephone
Facsimile
email
web
+44 (0)28 90 667 914
+44 (0)28 90 668 286
[email protected]
www.rpsgroup.com/ireland
On behalf of:
Sligo County Council
Market Yard Buildings
Market Yard
Sligo
Co. Sligo
Ireland
Telephone
Facsimile
email
web
071 9111960
071 9111990
[email protected]
sligococo.ie
The following sub-consultants carried out specialist studies
Aqua-fact International Limited
Natura Environmental Consultants
Michelle Cronin, BSc. MSc. PhD .
Paul Johnston
F.R. Mark and Associates
ADCO
Raymond Burke Consulting
Intertidal and Underwater Ecology
Birds
Marine Mammals
Fisheries
Noise and Vibration Impact
Intertidal and Underwater Archaeological Impact
Economic Appraisal
B-16

Sligo Harbour - Department of Housing, Planning, Community and

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