Status of Beaches and Bays in Tobago

Mr. Christopher Alexis Oceanography and Coastal Processes 1 Outline —  Introduction
—  Research Objectives
—  Methodology
—  Results
—  Conclusions
—  Recommendations
2 Introduc:on —  C.C.P. coastal geomorphological data (beach profiles) systematically
collected from 1980’s. Currently a collaboration with DNRE of THA
—  This paper focuses on 26 beaches and bays monitored, comprising 42
beach profiling stations around Tobago.
Englishman’s Bay Pigeon Point
3 Introduc:on —  Beaches and coastal dunes are depositional features found along
coasts.
—  Beaches are dynamic and respond to coastal forcing mechanisms.
—  Beach sediment is critical in the protection of the coastline by
dissipating wave energy; thereby acting as a buffer to erosion.
Englishman’s Bay, April 2013
4 Introduc:on How do we analyze the status of beaches? —  Beaches can either be classified as being in a state of Erosion,
Accretion or Dynamic Equilibrium (D.E.).
—  Erosion can occur either horizontally (where the coastline recedes)
or vertically (where the sand elevation decreases). “Net loss”
—  Accretion occurs when there is an increase in sediment along the
beach profile; both horizontally (increasing beach width) and
vertically (building the berm). “Net gain”
—  When these two cycles of erosion and accretion occur without any
long term deleterious effects on the beach, a state of Dynamic
Equilibrium (DE) is said to exist (Van Rijn 1998).
—  No net loss or net gain of sediment
5 Introduc:on —  Beaches however are damaged by sand removal (erosion or
mining), badly designed coastal protection structures or any
activity that prevents sediment sources from replenishing them.
Great Courland Bay, 2008 wave event
Pigeon Point, 2008
6 Research Objec:ves —  To investigate the littoral, morphological and sedimentological
characteristics of beaches and bays.
—  To identify the effects of tidal cycles and seasons.
—  To identify the effects of extreme events (Storms, Hurricanes and
Anthropogenic Changes)
—  To evaluate and monitor erosion and accretion rates.
—  To monitor the stability status and trends of beaches over a time-
series.
7 Methodology 8 Data Collected
—  1. Coastal Processes
—  2. Beach Morphology
—  3. Sediments
9 —  1. Coastal Processes:
(i) Wind Speed
(ii) Wind Direction
(iii) Wave Period
(iv) Wave and Breaker Height
(v) Wave and Breaker Angle
(vi) Breaker Type
(vii) Longshore Currents:
(a) Current Speed
(b) Current Direction
10 —  2. Beach Morphology:
(i) Beach Profiles
(ii) Beach Plan
(iii) Beach Orientation
(iv) Coastline Retreat
Beach profiling done using standard surveying
methods as described by Goudie (1990).
—  3. Sediments:
(i) Upper Foreshore (MHWM)
(ii) Mid-Beach
(iii) Lower Foreshore (MLWM)
Sediments are dry sieved to obtain Folk & Ward
(1957) parameters. (mean, sorting, skewness
& kurtosis)
11 Map of Tobago Showing IMA Sta:ons Selected Results 13 Coastal Classifica:on Map of Tobago Sediment Analysis —  Beaches are an accumulation of sediments ranging in size from
silt to pebble and cobble sizes.
—  Generally, coarser sediments are associated with steeper beach
face gradients and vice-versa.
—  Beach sediment around Tobago generally consists of medium
grained sand that are well to moderately sorted.
—  Beaches that contain a matrix of both sand and pebble size
sediments have bi-modal distributions that are poorly sorted
e.g. Bloody Bay.
15 Goldsborough Bay
Sediment Histogram for Goldsborough Bay Sta:on 2 Percentage (%) 100 80 Normal distribution
60 UB 40 MB 20 LB 0 Black Sand
-­‐2 -­‐1 0 1 2 3 4 Sediment Size (Phi) Pigeon Point
Percentage(%) Sediment Histogram for Pigeon Point Station 2 Sand
100 90 80 70 60 50 40 30 20 10 0 Bi-modal
Poorly Sorted
UB MB LB -­‐2 -­‐1.5 -­‐1 -­‐0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 Pan Sediment size (Phi) Bloody Bay
Sediment Histogram for Bloody Bay 100 90 Matrix of Sand and
Pebbles
Percentage (%) 80 UB 70 Bi-modal
Poorly Sorted
60 50 MB LB 40 30 20 10 0 -­‐3 -­‐2 -­‐1 0 1 2 Sediment Size in (Phi ) 3 4 16 Sediment Analysis Leeward Coast Mean Grain Size Distribution 1.4 (Average Grain Size = 0.27 mm)
Mean Grain Size( mm) 1.2 1 0.8 0.6 0.4 0.2 0 Beach /Bay Std. Dev = ±0.28
1.31
Range = 0.17 –
17 Sediment Analysis Windward Coast Mean Grain Size Distribution 0.9 (Average Grain Size = 0.29 mm)
Mean Grain Size( mm) 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Beach /Bay Std. Dev = ±0.14
0.81
Range = 0.13 –
18 Stability Status of Beaches Leeward Coast
—  The leeward coast is open to the Caribbean Sea and exposed to
the Northeast Trade Winds and Mid-Atlantic storm swells.
—  These bays are exposed to moderate to high wave energy
where breaker heights can exceed 0.65 m.
—  All monitored beaches along this coast were in dynamic
equilibrium (DE) except:
—  Pigeon Point west
—  Mt. Irvine east
—  Little Back Bay west
Eroding
—  Stone Haven west
—  Pigeon point north
—  Mt. Irvine west
Accreting
19 20 Store Bay 1
Store Bay 2
21 Pigeon Point 1
Pigeon Point 1
Pigeon Point 2
Pigeon Point 3
22 Sheerbird’s 2
Sheerbird’s 1
23 Buccoo Bay 1
Buccoo Bay 2
24 Mount Irvine 1
Mount Irvine 2
25 Stone Haven 2
Stone Haven 1
26 Great Courland 2
Great Courland 1
Great Courland 3
Arnos Vale
Arnos Vale
Castara Bay
Culloden Bay
Parlatuvier Bay
Englishman’s Bay
Man O War Bay
Bloody Bay
Shoreline Stability Status of Leeward Coast Beaches Beach/Bay IMA’s Beach Monitoring Station Location Shoreline Stability Status (+Net Annual Accretion (m); -­‐Net Annual Erosion (m); DE Dynamic Equilibrium) Store Bay 1 2 2009 DE DE 2010 DE DE 2011 DE DE 2012 DE DE 2013 DE DE Pigeon Point 1 2 DE DE DE DE DE -­‐4.00 DE 16.00 DE DE 3 DE DE -­‐3.00 -­‐2.50 DE DE DE DE DE DE 1 DE DE DE DE DE 2 DE DE DE DE DE 1 2 DE DE DE DE DE DE DE DE DE DE Mt.Irvine 1 2 DE DE DE DE -­‐0.10 0.70 -­‐0.30 DE -­‐0.10 0.15 Little Back Bay 1 2 DE DE DE DE -­‐0.50 DE -­‐0.60 DE DE DE Stone Haven 1 2 DE DE DE -­‐0.10 DE DE DE DE DE -­‐0.10 Great Courland 1 2 DE DE DE DE DE DE DE DE DE DE Arnos Vale DE DE DE DE DE Culloden Bay DE DE DE DE DE Castara Bay DE DE DE DE DE Englishman's Bay DE DE DE DE DE Parlatuvier DE DE DE DE DE Bloody Bay DE DE DE DE DE Man Of War Bay DE DE DE DE DE Milford Bay Sheerbird’s Point Buccoo Bay PIGEON POINT, STATION 3 Pigeon Point Sta:on 3 2009-­‐2013 1.5 Erosion
Shoreline Recession
1.0 Eleva5on (m) 0.5 Mean Sea Level 0.0 -­‐0.5 10 15 20 25 30 35 Distance from Benchmark (m) PIGEON POINT -­‐ Station 3 Changes in Beach Widths and Volumes March 1991 -­‐ February 2013 30 Change in Beach Width Change in Beach Volume Linear (Change in Beach Width) Linear (Change in Beach Volume) y = -­‐0.0018x + 3.8856 R² = 0.7172 20 10 0 0 -­‐10 -­‐10 -­‐20 8500 9000 Number of Days (Units) 8000 2000 1500 1000 -­‐30 -­‐20 y = -­‐0.0023x + 4.6234 R² = 0.65834 500 Long-term analysis shows
negative changes to beach
width and volume.
30 10 0 — 
Beach profiles indicate
shoreline recession from
2009-2013.
Beach Width (m) 20 — 
40 Beach Volume (m3) 5 7500 -­‐2.0 -­‐5 0 7000 -­‐10 6500 -­‐15 6000 -­‐20 5500 -­‐25 5000 -­‐30 4500 -­‐35 4000 -­‐40 -­‐1.5 3500 -­‐45 -­‐1.0 3000 -­‐50 200907 201102 201203 201302 2500 200903 201011 201108 201206 201308 -­‐30 Mt. Irvine, Sta:on 1 Mount Irvine Bay Sta:on 1 2009-­‐2013 3.0 200903 201011 201108 201206 201308 2.5 2.0 1.5 200906 201102 201203 201302 Eleva5on (m) 1.0 0.5 0.0 -­‐0.5 -­‐1.0 -­‐1.5 -­‐2.0 -­‐2.5 25 30 35 MOUNT IRVINE BAY -­‐ Station 1 Changes in Beach Widths and Volumes March 1992 -­‐ August 2013 20 10 5 5 0 0 -­‐5 -­‐5 -­‐10 -­‐10 -­‐15 Number of Days (Units) 9000 8500 8000 7500 7000 6500 5500 -­‐20 5000 2000 1500 -­‐20 -­‐25 y = -­‐0.0002x -­‐ 0.1267 R² = 0.0418 Change in Beach Width Change in Beach Volume Linear (Change in Beach Width) Linear (Change in Beach Volume) 6000 -­‐15 1000 Long-term analysis indicates
beach is eroding slightly.
10 500 — 
Beach profiles indicate
dynamic equilibrium between
2009-2013.
15 y = 3E-­‐06x -­‐ 0.1071 R² = 1.2E-­‐05 0 — 
Beach Width (m) 15 20 Beach Volume (m3) 20 4500 15 4000 10 Distance from Benchmark (m) 3500 5 3000 0 2500 -­‐5 -­‐25 LiYle Back Bay, Sta:on 1 LiYle Back Bay Sta:on 1 2009 -­‐2013 4.0 200903 201011 201108 201206 201308 3.5 3.0 2.5 200906 201102 201203 201302 Eleva5on (m) 2.0 1.5 1.0 0.5 0.0 -­‐0.5 -­‐1.0 -­‐1.5 -­‐2.0 55 60 65 70 75 Distance from Benchmark (m) LITTLE BACK BAY -­‐ Station 1 Changes in Beach Widths and Volumes March 1992 -­‐ August 2013 40 20 20 0 0 -­‐20 -­‐20 -­‐40 -­‐40 -­‐60 Number of Days (Units) 9000 8500 8000 y = 0.0002x -­‐ 5.7999 R² = 0.0026 7500 2000 1500 -­‐80 1000 Change in Beach Width Change in Beach Volume Linear (Change in Beach Width) Linear (Change in Beach Volume) -­‐60 500 Long-term analysis indicates
erosion.
y = -­‐0.0016x -­‐ 4.2046 R² = 0.02926 0 — 
Beach profiles indicate
dynamic equilibrium during
2009-2013
Beach Width (m) — 
40 Beach Volume (m3) 50 7000 45 6500 40 6000 35 5500 30 5000 25 4500 20 4000 15 3500 10 3000 5 2500 0 -­‐80 Stone Haven Sta:on 2 2009 -­‐ 2013 Stone Haven Bay, Sta:on 2 3.5 200903 200906 201011 201102 201108 201203 3.0 2.5 1.5 1.0 0.5 0.0 -­‐0.5 -­‐1.0 -­‐1.5 -­‐2.0 -­‐2.5 50 55 60 65 70 75 STONE HAVEN -­‐ Station 2 Changes in Beach Widths and Volumes March 1992 -­‐ August 2013 20 20 10 y = -­‐0.0014x + 0.7280 R² = 0.1361 Beach Volume (m3) 0 0 -­‐10 -­‐10 -­‐20 -­‐20 9000 8500 Number of Days (Units) 8000 -­‐30 7500 2000 -­‐40 1500 Change in Beach Width Change in Beach Volume Linear (Change in Beach Width) Linear (Change in Beach Volume) -­‐30 1000 Long-term analysis indicate
erosion.
10 500 — 
Beach profiles indicate
dynamic equilibrium between
2009-2013
y = -­‐0.0042x + 8.2426 R² = 0.43263 0 — 
80 7000 45 6500 40 6000 35 5500 30 Distance from Benchmark (m) 5000 25 4500 20 4000 15 3500 10 3000 5 2500 0 Beach Width (m) Eleva5on (m) 2.0 -­‐40 Windward Coast
—  More exposed beaches and bays to the Atlantic Ocean and the
Northeast Trade Winds.
—  Coastal erosion has prompted construction of coastal defense
structures eg. seawalls and rip rap revetments.
—  Most stations on this coast were generally in a state of dynamic
equilibrium except:
—  Little Rockly west
—  Goldsborough Bay west
—  Barbados Bay west
—  King’s Bay
Eroding
Accreting
37 Anse Bateau
King’s Bay
Richmond
Goldsborough 1
Goldsborough 2
Pinfold Bay
Barbados Bay 3
Minister Bay
Rockly Bay
46 Little Rockly 2
Little Rockly 3
47 La Guira Bay
Canoe Bay
48 Shoreline Stability Status of Windward Coast Beaches Beach/Bay IMA’s Beach Monitoring Station Location Shoreline Stability Status (+Net Annual Accretion (m); -­‐Net Annual Erosion (m); DE Dynamic Equilibrium) Anse Bateux 1 2009 DE 2010 DE 2011 DE 2012 DE 2013 DE King's Bay 1 DE DE DE DE 0.10 1 DE DE DE DE -­‐0.20 1 2 DE DE DE DE DE DE DE DE DE -­‐3.00 1 DE DE DE DE DE 1 DE DE DE DE DE 2 DE DE DE DE DE 3 DE -­‐0.10 DE -­‐0.20 -­‐0.30 1 DE DE DE DE DE Rockly 1 2 DE DE DE DE DE DE DE DE DE DE Little Rockly 2 DE DE DE DE DE 3 DE DE -­‐1.50 DE DE Canoe Bay 1 DE DE DE DE DE La Guira 1 2 DE DE DE DE DE DE DE DE DE DE Richmond Bay Goldsborough Pinfold Barbados Bay Minister Bay Richmond Bay 2009 -­‐ 2013 RICHMOND BAY 3.0 200903 201011 201108 201206 201305 Cliff recession
2.5 2.0 1.0 0.5 0.0 -­‐0.5 -­‐1.0 -­‐1.5 -­‐2.0 -­‐2.5 35 40 45 50 RICHMOND BAY Changes in Beach Widths and Volumes January 1993 -­‐ May 2013 30 30 Change in Beach Width Change in Beach Volume Linear (Change in Beach Width) Linear (Change in Beach Volume) y = -­‐0.0026x -­‐ 1.3285 R² = 0.47551 20 10 10 0 0 -­‐10 -­‐10 -­‐20 Number of Days (Units) 9000 8500 8000 7500 7000 6500 6000 5500 2000 1500 -­‐30 -­‐20 y = -­‐0.0013x + 5.1157 R² = 0.2397 1000 Long-term analysis illustrates
negative changes to beach
volume.
20 500 — 
Beach profiles indicate cliff
recession from 2009-2013.
0 — 
55 Beach Volume (m3) 30 5000 25 4500 20 Distance from Benchmark (m) 4000 15 3500 10 3000 5 2500 0 Beach Width (m) Eleva5on (m) 1.5 200907 201102 201203 201302 -­‐30 Barbados Bay Sta:on 3 2009-­‐2013 4.5 4.0 Cliff recession 3.5 Barbados Bay, Sta:on 3 200910 201011 201102 201108 201203 3.0 2.0 1.5 1.0 0.5 0.0 -­‐0.5 -­‐1.0 -­‐1.5 -­‐2.0 30 35 40 45 50 Distance from Benchmark (m) BARBADOS BAY -­‐ Station 3 Changes in Beach Widths and Volumes May 2009 -­‐ January 2013 Change in Beach Width Change in Beach Volume Linear (Change in Beach Width) Linear (Change in Beach Volume) 40 40 30 y = -­‐0.0006x -­‐ 1.9084 R² = 0.00515 20 20 10 10 0 0 Number of Days (Units) -­‐10 9000 5000 4500 4000 3500 3000 2500 2000 1500 -­‐20 8500 y = 0.0008x -­‐ 1.2490 R² = 0.0107 -­‐10 1000 Long-term analysis net
negative change to beach
width and sand volumes.
30 500 — 
Beach profiles indicate
dynamic equilibrium between
2009-2013
0 — 
50 -­‐20 Beach Volume (m3/m) 50 8000 25 7500 20 7000 15 6500 10 6000 5 5500 0 Beach Width (m) Eleva5on (m) 2.5 GOLDSBOROUGH BAY , STATION 2 Goldsbourough Bay Sta:on 2 2009-­‐2013 2.5 200903 201011 201108 201206 201308 2.0 1.5 0.5 0.0 -­‐0.5 -­‐1.0 -­‐1.5 -­‐2.0 -­‐2.5 -­‐3.0 -­‐3.5 40 45 50 55 GOLDSBOROUGH BAY -­‐ Station 2 Changes in Beach Widths and Volumes July 2000 -­‐ August 2013 30 20 10 y = -­‐0.0045x + 3.8897 R² = 0.61506 0 0 -­‐10 -­‐10 9000 8500 -­‐20 8000 7500 7000 6500 Number of Days (Units) 6000 5000 4500 2000 -­‐30 5500 y = -­‐0.0015x + 2.6844 R² = 0.2121 -­‐20 1500 Long-term analysis shows
negative changes to beach
volume and width.
10 1000 — 
Beach profiles suggest
dynamic equilibrium between
2009-2013.
20 500 — 
There is evidence of sand
mining along the beach.
0 — 
30 Change in Beach Width Change in Beach Volume Linear (Change in Beach Width) Linear (Change in Beach Volume) Beach Volume (m3) 20 25 30 35 Distance from Benchmark (m) 4000 15 3500 10 3000 5 2500 0 Beach Width (m) Eleva5on (m) 1.0 200906 201102 201203 201302 -­‐30 LiYle Rockly Bay, Sta:on 2 LiYle Rockly Bay Sta:on 2 2009 -­‐2013 2.0 200903 200906 201011 201102 201108 201203 1.5 0.5 0.0 -­‐0.5 -­‐1.0 -­‐1.5 -­‐2.0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 Distance from Benchmark (m) LITTLE ROCKLY BAY -­‐ Station 2 Changes in Beach Widths and Volumes January 2004 -­‐ August 2013 30 Beach Volume (m3) 25 20 10 15 0 10 5 -­‐10 y = -­‐0.0015x + 1.0536 R² = 0.15716 0 -­‐20 9000 8500 8000 7500 7000 Number of Days (Units) 6500 6000 5500 5000 4500 4000 3500 3000 2500 2000 1500 -­‐30 -­‐5 y = -­‐0.0011x -­‐ 4.6905 R² = 0.0313 1000 Long-term analysis shows
negative trends in beach
volumes and widths.
20 500 — 
The beach profiles conducted
over the study period suggest
dynamic equilibrium.
30 Change in Beach Width Change in Beach Volume Linear (Change in Beach Width) Linear (Change in Beach Volume) 0 — 
Beach Width (m) Eleva5on (m) 1.0 -­‐10 Conclusion 54 Conclusion —  Most of the beaches and bays monitored between 2009-2013 were
in a state of D.E.
—  The leeward coast beaches are predominantly stable and in
dynamic equilibrium, with accretion occurring at 3 beaches.
—  Although backed by resistant metamorphic rocks in its north-
eastern region, erosion was sometimes observed as a lowering of
sand levels and not as a result of cliff recession.
—  On the windward coast, most beaches experience dynamic
equilibrium, with some erosion due to shoreline recession.
—  The long term analysis for Goldsborough Bay illustrated that
although the beach is dynamic it can be negatively impacted by
sand mining.
55 Coastline Stability Map of Tobago Recommendations 57 Recommenda:ons —  There are areas along the coastline that are not monitored but
accessible such as Queen’s Beach.
—  For larger bays additional stations may be necessary to capture the
changes taking place since it is not always reflected in the current
IMA monitoring stations.
—  La Guira Bay
—  Minister Bay
—  King’s Bay
—  Richmond Bay
—  Goldsborough Bay
58 Why do this? 59 What does this mean? —  Informs decisions on coastal policy and development:
ICZM
—  Setback distances for development
— 
—  Highlights priority areas (coastal protection)
—  Establishes baseline for future studies
60 Thank You! 61