Sedimentation in the Botlek Harbour

Transcription

Sedimentation in
the Botlek Harbour
A research into driving water exchange mechanisms
Port Research Centre
Sedimentation in
the Botlek Harbour
A research into driving water exchange mechanisms
January 2013, Adil El Hamdi
ISBN/EAN: 978-94-6186-126-9
NUR-code: 950
Reeksnummer: 41
© Port Research Centre Rotterdam-Delft.
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Sedimentation in the Botlek Harbour
A research into driving water exchange mechanisms.
Master Thesis
Final Report
Adil EL HAMDI
Jan 2011
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Thesis Committee:
Prof. ir. T. Vellinga
A. Noordijk
Prof. dr. ir. H. Winterwerp
P. Taneja
Technical University of Delft / Port of Rotterdam
Port of Rotterdam
Technical University of Delft / Deltares
Technical University of Delft
Prof. Cheong Hin Fatt
Dr. M. Chui Ting Fong
National University of Singapore
Contact:
Port of Rotterdam
Postbus 6622
3002 AP Rotterdam
The Netherlands
Postbus 5
2600 AA Delft
The Netherlands
21 Lower Kent Ridge Road
Singapore 119077
Singapore
T +31 (0)10 252 10 10
E [email protected]
I www.portofrotterdam.com
T +31 (0)15 27 89 111
E [email protected]
I www.tudelft.nl
T +65 6516 6666
E [email protected]
I www.nus.edu.sg
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ACKNOWLEDGEMENT
In front of you is the final report of my Master thesis. The thesis forms the final part of my Double
Master Programme ‘Hydraulic Engineering and Water Resource Management’. I took this
programme at the Technical University of Delft and the National University of Singapore. The
research itself was done the Port of Rotterdam. Hereby I want to thank the colleagues of the Port of
Rotterdam for supporting me during my research.
However I want to thank the thesis committee in particular, for their guidance and help. The
committee members:
Prof. ir. T. Vellinga ( Head committee)
A. Noordijk
Prof. dr. ir. H. Winterwerp
P. Taneja
Prof. Cheong Hin Fatt
Dr. M. Chui Ting Fong
Technical University of Delft / Port of Rotterdam
Port of Rotterdam
Technical University of Delft / Deltares
And of course I would like to thank my family and my friends too for their support.
Rotterdam, jan 2012
Adil El Hamdi
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SUMMARY
Siltation of harbour basins and navigation channels is a serious problem in the port of Rotterdam as well
in many other harbours all over the world. Due to siltation, basins and channels require frequent
maintenance dredging to guarantee safe navigational depths. The costs associated with these dredging
activities are quite high.
To keep the channels and harbours in Rotterdam navigable, Rijkswaterstaat and the Port of Rotterdam
are dredging approximately 15 million m3 of sediment a year. The dredging cost of the Botlek Harbour
only is already about 3 million Euros a year. It is a task to keep the costs in the Port of Rotterdam as low
as possible to compete with other ports. Reducing maintenance dredging costs is in line with the goal of
the Port of Rotterdam to be the most competitive, innovative and sustainable port in the world.
Most sedimentation within the maintenance area of the Port of Rotterdam occurs in the Botlek.
According data, between 1.5 and 3 million m3/year is dredged in the Botlek Harbour. Although the
current dredging philosophy more or less works, the question arises whether there are solutions that
are more cost-effective. However, the problem is so complex that it narrowed down for the sake of
research quality.
The main causes of siltation in general and specifically in the Botlek Area form an important part of the
study. Hydrodymical models (SIMONA & Delft3D), were used to gain insight in the sedimentation
problem. The focus in this thesis was more on the hydrodynamics. The exchange mechanisms between
the river and Botlek Harbour were investigated, which were needed to examine the effectiveness of
certain solutions. In practice a lot of solutions are proposed in literature, however in this study only a
couple of ‘hard’ measures are investigated. The first possible solution that was examined was the use of
a Current Deflecting Wall. It turned out that the hydrodynamics were very sensitive to the configuration
of the CDW. While sometimes it would lower the exchange flow, at other cases it would even make the
problem worse. The second solution was to make a gap in the Geulhaven dam. However this was not a
good solution as high exchange flows occurred. The last proposed solution, the filling of the underwater
dam, seemed more feasible as it would decrease the exchange flow according the numerical models.
The research has first order results which can be used in further studies. According to this results,
certain solutions will decrease the exchange flows. On turn it would very likely result in lower
sedimentation rates in the Botlek Area. It is expected that some CDW configurations and the filling of
the underwater dam would have a positive effect when it comes to sedimentation. However, this
research is the first step of an extensive study that must made to deal with the problem.
First of all many things can be done to improve the models, for example by using a higher spatial
resolution. Secondly, other sets of conditions must be modelled to see what kind of effect this has on
exchange flows. In addition, sediment must be included in the models to have more insight on the
sedimentation itself. The next step would be a feasibility study, including a cost benefit analysis. It would
be wise to improve the models further and to make a scale model for the most feasible solution. In the
ideal case, were all steps are positive and hard conclusion can be made, it would be a good idea for the
Port of Rotterdam to start a pilot.
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TABLE OF CONTENT
Acknowledgement ........................................................................................................................ 6
Summary ...................................................................................................................................... 8
List of figures ...............................................................................................................................14
List of tables ................................................................................................................................18
1
Introduction .........................................................................................................................20
1.1
2
3
Problem description ......................................................................................................20
1.1.1
General .................................................................................................................20
1.1.2
Botlek Harbour ......................................................................................................20
1.2
Current approach ..........................................................................................................22
1.3
Research goal and questions ..........................................................................................23
System .................................................................................................................................26
2.1
System boundaries ........................................................................................................26
2.2
Site Conditions ..............................................................................................................26
Literature review ..................................................................................................................28
3.1
Estuarine hydrodynamics ...............................................................................................28
3.2
Sediment transport and morphology ..............................................................................30
3.2.1
Sediment properties...............................................................................................30
3.2.2
Non-cohesive sediment properties..........................................................................31
3.2.3
Motion and transport .............................................................................................31
3.2.4
Cohesive sediment and fluid mud ...........................................................................32
3.3
Turbidity maximum .......................................................................................................34
3.4
Reducing costs ..............................................................................................................35
3.5
Measures applied in the past .........................................................................................36
3.5.1
Siltation trap ..........................................................................................................36
3.5.2
Silt screen ..............................................................................................................37
3.6
Minimising harbour siltation ..........................................................................................39
3.6.1
Strategies ..............................................................................................................39
3.6.2
Exchange mechanisms............................................................................................39
3.6.3
Possible solutions...................................................................................................46
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Dredge data analysis .............................................................................................................50
5
Research Strategies and approach .........................................................................................52
6
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5.1
Strategies......................................................................................................................52
5.2
Use of models ...............................................................................................................52
Hydrodynamical models........................................................................................................54
6.1
Software .......................................................................................................................54
6.2
Model equations and assumptions .................................................................................55
6.3
Available models ...........................................................................................................55
6.4
Adjusted model .............................................................................................................57
6.4.1
Boundaries ............................................................................................................57
6.4.2
Hydrodynamical boundary conditions .....................................................................60
6.4.3
Resolution choice...................................................................................................60
Determination of circulations ................................................................................................66
7.1
Horizontal vs. vertical circulation ....................................................................................66
7.2
Formulation ..................................................................................................................66
7.3
Cross sections ...............................................................................................................68
7.4
Data handling and script ................................................................................................69
7.5
Model input ..................................................................................................................70
7.5.1
SIMONA ................................................................................................................70
7.5.2
Delft-3D ................................................................................................................70
7.6
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First results ...................................................................................................................71
7.6.1
Comparison – water level .......................................................................................71
7.6.2
Comparison – salinity .............................................................................................72
7.6.3
Initial field .............................................................................................................73
7.6.4
Comparison with measurements– flow velocities.....................................................74
7.6.5
Flow pattern ..........................................................................................................74
7.6.6
Horizontal circulation – qualitative ..........................................................................81
7.6.7
Circulation – quantitative .......................................................................................82
Contribution exchange mechanisms ......................................................................................84
8.1
Decomposition method .................................................................................................84
8.2
Contribution of the three mechanisms ...........................................................................84
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8.2.1
Cross section A ......................................................................................................86
8.2.2
Cross section B.......................................................................................................87
8.2.3
Cross section C.......................................................................................................88
8.3
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Analysis ........................................................................................................................89
Exchange mechanisms and sedimentation .............................................................................90
9.1
Sediment concentration measurements .........................................................................90
9.2
Combination of results...................................................................................................91
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Measures .........................................................................................................................96
10.1
Solutions to be investigated ...........................................................................................96
10.2
Current Deflecting Wall .................................................................................................98
10.2.1
Variant 1 ...............................................................................................................98
10.2.2
Variant 2a..............................................................................................................98
10.2.3
Variant 2b..............................................................................................................99
10.2.4
Variant 3 ...............................................................................................................99
10.3
Hole in Dam ................................................................................................................ 100
10.3.1
Variant 1 ............................................................................................................. 100
10.3.2
Variant 2 ............................................................................................................. 100
10.4
Filling underwater dam ................................................................................................ 101
10.4.1
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Variant 1 ............................................................................................................. 101
Results ........................................................................................................................... 102
11.1
No measures ............................................................................................................... 102
11.2
Current Deflecting Wall ............................................................................................... 103
11.2.1
Variant 1 ............................................................................................................. 103
11.2.2
Variant 2a............................................................................................................ 104
11.2.3
Variant 2b............................................................................................................ 105
11.2.4
Variant 3 ............................................................................................................. 106
11.3
Hole in Dam ................................................................................................................ 107
11.3.1
Variant 1 ............................................................................................................. 107
11.3.2
Variant 2 ............................................................................................................. 108
11.4
Filling underwater dam ................................................................................................ 109
11.4.1
11.5
Variant 1 ............................................................................................................. 109
Discussion ................................................................................................................... 110
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11.5.1
Density currents................................................................................................... 110
11.5.2
Horizontal exchange............................................................................................. 110
11.5.3
Tidal filling ........................................................................................................... 111
11.5.4
Total ................................................................................................................... 112
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Conclusion, Discussion & Recommendation ...................................................................... 114
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Literature ....................................................................................................................... 118
Appendix A – Map Port of Rotterdam .......................................................................................... 122
Appendix B – Dredge Atlas Botlek ............................................................................................... 128
Appendix C – Dredge data 1995-2010, Botlek Area ...................................................................... 130
Appendix D – Assumptions and approximations D3D ................................................................... 132
Appendix E – Cross sections mouth Botlek ................................................................................... 134
E.1 – Cross section A ............................................................................................................... 134
E.2 – Cross section B ............................................................................................................... 134
E.3 – Cross section C ............................................................................................................... 135
Appendix F – Used depths for script ............................................................................................ 136
Appendix G – Transformation σ to z-plane ................................................................................... 138
Appendix H – Part of Matlab script .............................................................................................. 140
Appendix I – Observation points. ................................................................................................ 148
Appendix J – Validation flow velocities ........................................................................................ 150
Appendix K – Depth averaged velocity profile - CDW – Variant 1 .................................................. 158
Appendix L – Depth averaged velocity profile - CDW – Variant 2a................................................. 162
Appendix M – Depth averaged velocity profile - CDW – Variant 2b ............................................... 166
Appendix N – Depth averaged velocity profile - CDW – Variant 3 ................................................. 170
Appendix O – Depth averaged velocity profile - Hole in dam – Variant 1 ....................................... 174
Appendix P – Depth averaged velocity profile - Hole in dam – Variant 2 ....................................... 178
Appendix Q – Depth averaged velocity profile - Filling underwater dam – Variant 1 ...................... 182
Appendix R – Horizontal flow pattern around Botlek mouth ......................................................... 186
Appendix S – Total flow through cross sections ............................................................................ 192
Appendix T – Decomposed flow through cross sections ................................................................ 198
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LIST OF FIGURES
Figure 1.1 – Area.
Figure 1.2 – Volume maintenance dredging a year in the Botlek area (source: Database PoR).
Figure 1.3 – Current dredging philosophy.
Figure 2.1 – Rijn-Maas estuarine system and boundaries.
Figure 2.2 – Mean tide at Hoek van Holland at mean discharge (Getijtafel 1991.0).
Figure 2.3 – Spring, neap and mean tide at Hoek van Holland. Lobith discharge 2200 m3/s
(Stroomatlas v3).
Figure 3.1 – Classification of estuaries on the basis of vertical structure of salinity.
Figure 3.2 – Salt wedge estuary.
Figure 3.3 – Partially mixed estuary.
Figure 3.4 – Well mixed estuary.
Figure 3.5 – Sediment classification (Wentworth, 1922).
Figure 3.6 – Sediment transport.
Figure 3.7 – Schematic representation of the governing processes between suspension layer and fluid
mud layer. A two layer approach (Winterwerp, 2010).
Figure 3.8 – Schematic description of mud transports (Winterwerp & van Kesteren, 2004).
Figure 3.9 – Lagrangian sketch of harbour siltation under typical hydrodynamic conditions (from: de
Nijs).
Figure 3.10 – Siltation trap at entrance Europoort/Maasvlakte.
Figure 3.11 – Siltation trap at the Botlek entrance.
Figure 3.12 – Placement of the test silt screen.
Figure 3.13 – Design low silt screen.
Figure 3.14 – The mixing layer in the harbour entrance.
Figure 3.15 – Horizontal entrainment mechanism.
Figure 3.16 – Tidal filling and emptying.
Figure 3.17 – Sketch exchange harbour basin – river.
Figure 3.18 – Currents in a tidal harbour a) ebb, b) flood.
Figure 3.19 – Schematisation the components and the combinations of the three.
Figure 3.20 – Row of poles and the corresponding velocity profile.
Figure 3.21 – Current deflecting wall with sills.
Figure 3.22 – Flow pattern. Without and with CDW.
Figure 3.23 – Silt trap.
Figure 3.24 – Egss of Thijsse.
Figure 3.25 – Pneumatic barrier.
Figure 4.1 – Dredged m3 per m2 a year. According data from 1995-2010. (Databaste PoR, 2011).
Figure 4.2 – Costs per m3. According data from 2010. (Database PoR, 2011).
Figure 5.1 – Model validation and calibration.
Figure 6.1 – SIMONA and D3D model.
Figure 6.2 – Paths from centre mouth Botlek.
Figure 6.3 – Estimation tidal excursion (W-E).
Figure 6.4 – Estimation tidal excursion (W - SE).
Figure 6.5 – Large and small model.
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Figure 6.6 – Boundary conditions large and small model.
Figure 6.7 – Model B: Coarse overall, fine local. Shades show the depth contour (Note: legend scale
not fixed).
Figure 6.8 – Relation resolution - computation time.
Figure 6.9 – Courant numbers model B.
Figure 7.1 – Hypothetical cross section harbour mouth.
Figure 7.2 – Horizontal and vertical circulation.
Figure 7.3 – The three cross sections and corresponding observation points at the Botlek mouth.
Figure 7.4 – Scheme to determine the relative contribution of horizontal and vertical circulation.
Figure 7.5 – Initial salinity field (in ppt’s).
Figure 7.6 – Flow pattern at -6 H w.r.t. HW Botlek.
Figure 7.12 – Flow pattern at HW Botlek.
Figure 7.13 – Flow pattern at +1 H w.r.t. HW Botlek.
Figure 7.19 – Vortex at the Botlek mouth.
Figure 8.1 – From two to three components.
Figure 8.2 – Water level of a tide according the model (from LW Botlek to LW Botlek).
Figure 8.3 – Discharge through cross section B according the model (from LW Botlek to LW Botlek).
Positive is harbour outflow, negative is harbour inflow.
Figure 8.4 – Distribution components over time (Cross-section A).
Figure 8.5 – Distribution components over time (Cross-section B).
Figure 8.6 – Distribution components over time (Cross-section C).
Figure 8.7 – Contribution of the three components to the horizontal and vertical circulation.
Figure 9.1 – Measuring stations of the de Nijs’ survey on the 11 th of April 2006 (De Nijs, 2010).
Figure 9.2 – The recorded water level, salinity and suspended particulate matter (top to bottom) at
station 2 on the 11th of April 2006. Open circles are near bead measurements and dots are near
surface measurements (De Nijs, 2010).
Figure 9.3 – Combined results: exchange flows (cross section B) and sediment concentration (De Nijs,
2010).
Figure 9.4 – Goal 1: lowering of the exchange flows in general.
Figure 9.5 – Goal 2: Low flow rates at times of high concentrations.
Figure 10.1 – Mismatch cell boundaries and CDW.
Figure 10.2 – No smooth boundaries possible.
Figure 10.3 – CDW – Variant 1.
Figure 10.4 – CDW – Variant 2a.
Figure 10.5 – CDW – Variant 2b.
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Figure 10.7 – Hole in dam – Variant 1.
Figure 10.9 – Filling underwater dam – Variant 1.
Figure 11.2 – CDW – Variant 1. Exchange mechanisms before and after, cross section B.
Figure 11.3 – CDW – Variant 1. Lay-out.
Figure 11.4 – CDW – Variant 2a. Exchange mechanisms before and after, cross section B.
Figure 11.5 – CDW – Variant 2a. Lay-out.
Figure 11.6 – CDW – Variant 2b. Exchange mechanisms before and after, cross section B.
Figure 11.7 – CDW – Variant 2b. Lay-out.
Figure 11.10 – Hole in dam – Variant 1. Exchange mechanisms before and after, cross section B.
Figure 11.11 – Hole in dam – Variant 1. Lay-out.
Figure 11.14 – Filling underwater dam – Variant 1. Exchange mechanisms before and after, cross
section B.
Figure 11.15 – Filling underwater dam – Variant 1. Lay-out.
Figure 12.1 – Steps to be taken.
Figure 0.1 – Dredge atlas.
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LIST OF TABLES
Table 1-1 – Research questions.
Table 3-1 – Narrowing harbour entrance. Advantages and disadvantages.
Table 3-2 – Row of poles. Advantages and disadvantages.
Table 3-3 – CDW. Advantages and disadvantages.
Table 3-4 – Sill. Advantages and disadvantages.
Table 3-5 – Silt trap. Advantages and disadvantages.
Table 3-6 – Egss of Thijsse. Advantages and disadvantages.
Table 3-7 – Pneumatic barrier. Advantages and disadvantages.
Table 6-1 – Coarse and Fine model.
Table 6-2 – Computation time / simulated time for different combinations. (*Single precision).
Table 7-1 – SIMONA Boundary conditions (provided by the Port of Rotterdam).
Table 7-2 – Simulations with and without salinity at different time steps.
Table 7-3 – Delft3D Parameters (* only required if salinity is turned on).
Table 7-4 – Comparing different time steps.
Table 7-5 – Comparing different time steps and analysing the spin-up time.
Table 7-6 – Initial values at several locations.
Table 7-7 – Average circulation at cross section A.
Table 7-8 – Average circulation at the three cross sections using lowest time step.
Table 8-1 – Distribution and cell & time averaged discharge for the three components at section A.
Table 8-2 – Distribution and cell & time averaged discharge for the three components at section B.
Table 8-3 – Distribution and cell & time averaged discharge for the three components at section C.
Table 11-1 – CDW – Variant 1. Values before and after.
Table 11-2 – CDW – Variant 2a. Values before and after.
Table 11-3 – CDW – Variant 2b. Values before and after.
Table 11-5 – Hole in dam – Variant 1. Values before and after.
Table 11-7 – Filling underwater dam – Variant 1. Values before and after.
Table 11-8 – Effects of measures on density currents.
Table 11-9 – Effects of measures on the horizontal exchange.
Table 11-10 – Effects of measures on tidal filling.
Table 11-11 – Effects of measures on total exchange flow.
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1 INTRODUCTION
1.1 Problem description
1.1.1
General
Siltation of harbour basins and navigation channels is a serious problem in the port of Rotterdam as
well in many other harbours all over the world. Due to siltation, these basins and channels require
frequent maintenance dredging to guarantee safe navigational depths. The costs associated with
these dredging activities are quite high.
The maritime sector and the vessel size grew rapidly in the last few decades. The current scale
increase requires deeper channels and harbours. As this increase is expected to continue in the
future, the required navigational depth increases as well. Intuitively, this will lead to even more
necessary maintenance dredging. All over the world (port-) authorities are trying to reduce
sedimentation in order to decrease the dredging costs. This is rather very difficult to achieve as
siltation is a very complex phenomena and hard to influence. Many possible solutions are proposed
by experts to reduce the sedimentation of harbours. However some solutions require huge
investments while their applicability and suitability in a particular harbour is not fully proven.
Therefore most authorities are not willing to take any risk and adhere to regular maintenance
dredging.
1.1.2
Botlek Harbour
The siltation problem in Rotterdam started in the period from 1957 till 1974 when the port was
expanded by the construction of the Botlek, Europoort and Maasvlakte. In the meantime the
channels Eurogeul, Maasgeul, Maasmond, Caland- and Beerkanaal, and the harbour basins where
deepened to receive larger vessels (MKO, 1987). This development had some serious negative side
effects. The morphological and hydrological balance of the system was disturbed. As a result of this
disturbance, nature wants to go back to its equilibrium situation and therefore sedimentation and/or
erosion occurs. In the case of Rotterdam it is mainly sedimentation and not erosion, due to the deep
maintenance depths. An additional effect of the disturbance is that salt water intrudes further in the
estuary system which in turn can affect the ecology and the fresh water supply.
To keep the channels and harbours in Rotterdam navigable, Rijkswaterstaat and the Port of
Rotterdam are dredging approximately 15 million m3 per year: about two-third by Rijkswaterstaat,
and one-third of the amount by the Port of Rotterdam. While Rijkswaterstaat is responsible for the
main waterways (Maasmond, Maasgeul, Nieuwe Waterweg and Nieuwe Maas, Oude Maas), the Port
of Rotterdam mainly takes care of the harbour basins and their entrances. The fact that two parties
are responsible for the maintenance of the contract depth instead of one, makes the implementation
of a possible solution a bit more complicated. The more stakeholders involved, the harder it is to
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compromise. Most sedimentation within the maintenance area of the Port of Rotterdam occurs in
the Botlek (Figure 1.1). At this moment between 1.2 and 2.5 million m3/year is dredged in the Botlek
Harbour according to data from 1995 until now (Figure 1.2). The cubic meters can be equated to kilos
if the density of the dredged material is known. Mostly this density is estimated as it is not known a
priori.
Figure 1.1 – Area.
Figure 1.2 – Volume maintenance dredging a year in the Botlek area (source: Database PoR).
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1.2 Current approach
The current handling of the siltation problem uses a corrective approach as shown in Figure 1.3. The
bathymetry is measured at regular intervals by a survey boat. The data is then compared with the
required depths, the so called contract depths which can be found in the ‘dredging atlas’ (see page
128). Subtracting these figures indicates the areas where dredging is required.
Figure 1.3 – Current dredging philosophy.
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1.3 Research goal and questions
It is a task to keep the (maintenance dredging) costs in the Port of Rotterdam as low as possible to
compete with other ports. Reducing maintenance dredging costs is in line with the goal of the Port of
Rotterdam to be the most competitive, innovative and sustainable port in the world. As mentioned
before, most of these maintenance dredging cost for the Port of Rotterdam Authority is due to the
siltation in the Botlek Harbour. The topic of the thesis is:
“ Sedimentation in the Botlek Harbour –
A research into driving water exchange mechanisms”.
Although the current approach described in the previous section more or less works, the question
arises whether there are solutions that are more cost-effective. Intuitively one would opt for a
preventive approach instead of a corrective one, namely preventing the sediment from coming into
the harbour. This method is described by in PIANC as KSO: Keep Sediment Out (PIANC 2006). With
respect to this method the corresponding thesis question could be: “How to prevent sediment
intruding the Botlek Harbour?” Before a thorough study can be made to answer this question, we
should consider whether this is actually desirable. Preventing the siltation of the Botlek Harbour,
while siltation rates elsewhere increase is definitely not the solution. This is simply shifting the
problem from one harbour to another one. This can only be attractive if the overall maintenance
dredging costs decreases. It must be taken into account that every proposed solution must be seen in
the system’s perspective and the main objective must kept in mind: reducing the dredging costs.
There are two other strategies that can be implemented, as regards to sediments: Keep Sediment
Moving or Keep Sediment Navigable. A research question could then be “How to keep sediment
moving?” or “How to accept sediment such that the ships can sail through it”.
Up till now sediment itself is considered as the main problem of the high dredging costs. However,
there are many factors than can influence the dredging costs. Perhaps the current dredging pro cess
could be optimised. It is wise to get an overview of all possible solutions in the beginning stage of the
study. When, during the study, more is known about the hydrodynamic and morphological
conditions of Rotterdam harbour area and the dredging processes, some solutions will prove to be
more attractive than others. The main question of this thesis can be summarized as follows:
“ How can the siltation in the Botlek be reduced, in order to reduce the total maintenance dredging
cost for the Port of Rotterdam ? ”
It must be kept in mind that the overall main goal is to decrease the costs. Only solutions which are in
a large extent cost effective for the Port of Rotterdam and more or less also for other parties, are
acceptable. First of all a research as to the possible cause of the sedimentation in general must be
carried out. Secondly we have to find out why siltation rates are high in the Botlek Harbour. In order
to answer these questions, it is wise to analyse the available data. This will give insight in whether a
trend can be identified in the volumes of maintenance dredging. If a pattern is discovered we
investigate how this trend has developed. This might or might not help to find an appropriate
solution.
23
Before brainstorming about the possible solutions for the given problem, it has to be investigated
what measures have been applied in the past. From this lessons can be learned, which can be very
useful when thinking about new possible solutions. Especially because every harbour is unique and
has its own conditions. Also more lessons can be learnt from experiences in other harbours all over
the world. A large variety of solutions exist, because different strategies can be applied. The question
arises which strategy is the most suitable one in this case.
Possible solutions and their impacts on siltation must be explored. This forms the core of the thesis
which at best results in an innovative, cost effective and sustainable solution. All these sub-questions
will lead towards the final answer of the main question. The topic is quite broad and it is easy to stray
from the subject. Therefore the main question is kept in mind all the time during the thesis. Table 1-1
summarises the research questions.
Main Question
Sub-question 1
Sub-question 2
Sub-question 3
Sub-question 4
Sub-question 5
“ How can the siltation in the Botlek be reduced, in order to
reduce the total maintenance dredging cost for the Port of
Rotterdam ?
“ What are the main causes of siltation, in general and specifically
in the Botlek Area ? “
“ Can a trend be recognized in the volumes of maintenance
dredging ? ”
“ Which measures have been undertaken in the past and how
effective were these measures ? “
“ Which strategy is the most suitable in order to decrease the
maintenance dredging costs ? “
“ What are possible cost-effective solutions for the port of
Rotterdam, and in particular the Botlek area, siltation problems ? “
Table 1-1 – Research questions.
24
25
2 SYSTEM
2.1 System boundaries
It was already clear in an early stage of the research that the problem should be solved in a system’s
perspective and not only in the Botlek Harbour area. The Rotterdam Waterway and its harbours form
part of a water system that is being influenced by tide and river discharges from the Rhine and
Meuse. However infrastructural changes, dredging policies and the “memory-effect” of the system
are also important parameters.
The water body can be classified as estuarine and includes the harbours and fairways of Rotterdam.
The figures below shows the Rhine-Meuse estuarine system and its boundaries (Figure 2.1). The upestuary boarders are approximately located at Hagestein (Lek), Tiel (Waal) and Lith (Maas). At the
other side the down-estuary borders are Hoek van Holland and the Haringvliet sluices. From 1970 on
these sluices regulate the distribution of fresh water over the Rotterdam Waterway (in Dutch:
Nieuwe Waterweg). Mainly fine and medium sand can be found at the bed of the Rotterdam
Waterway. Mostly sand is dredged in the fairways, while in the harbours typically mud is dredged.
Figure 2.1 – Rijn-Maas estuarine system and boundaries.
2.2 Site Conditions
The hydrodynamics in the system is mainly determined by:
- Tide
- River discharges
- Density differences
- Wind effects (set-up/set-down)
- The Haringvliet sluices programme
26
The tide, river discharges and the Haringvliet sluice programme form the most important boundary
conditions. Normally the tide at Hoek van Holland at the down-stream boundary is used to
determine the tide. This tide is semi-diurnal and has a mean tidal range of ± 1.75 m and ± 2.0 m at
spring and ± 1.2 m at neap (see Figure 2.2 and Figure 2.3).
Figure 2.2 – Mean tide at Hoek van Holland at mean discharge (Getijtafel 1991.0).
Figure 2.3 – Spring, neap and mean tide at Hoek van Holland. Lobith discharge 2200 m3/s (Stroomatlas v3).
The estuary’s fresh water is supplied by the river Rhine and the Meuse. The distribution of the fresh
water over the Rotterdam Waterway is regulated by the Haringvliet sluices according the discharge
programme LPH ’84. When the Rhine discharge is between 1700 and 3900 m3/s, about 1500 m3/s is
discharged through the Maasmond (Nieuwe Waterweg and Hartelkanaal). For Rhine discharges
lower than 1700 m3/s, the Haringvliet sluices are closed and all fresh water is discharged through the
Rotterdam Waterway.
27
3 LITERATURE REVIEW
3.1 Estuarine hydrodynamics
Estuaries can be classified according to either geomorphology or salinity (Nielsen, 2009). As can be
seen in Figure 3.1, based on salinity, three types can be distinguished: stratified estuary (sharp
interface), partly mixed estuary (gradually change in salinity vertically) and a well-mixed estuary
(strong vertical mixing).
Figure 3.1 – Classification of estuaries on the basis of vertical structure of salinity.
The tide that travels into the estuary is modified by the shoreline and by shallow water. The tidal
range at Hoek van Holland can be categorized as mesotidal.
There are typically three zones in an estuary: an outer zone where the salinity is close to that of the
open sea, a middle zone where there is rapid change in gradient and an upper/riverine zone, where
water may be fresh throughout the tide. Even though there is only 2% in different in density between
fresh (river) and salt water (sea), the horizontal and vertical gradients causes water circulatio n which
in turn results in trapping of sediment particles. The currents are variable both in time and space. The
three types of estuaries are described on the next page (Dyer 2001).
28
Figure 3.2 – Salt wedge estuary.
In salt wedge estuaries the river water tends to
flow out on top of the denser sea water that rest
almost stationary on the sea bed. A wedge of
salt water is formed, penetrating toward the
head of the estuary. This salt wedge has a sharp
salinity interface at the upper surface: a
halocline. Between the two layers there is
friction. The velocity shear between the almost
stationary salt wedge and rapidly flowing surface
layer produce small internal waves. As these
waves break, entrainment is caused: some of the
salty water goes to the upper layer. Salt wedge
estuaries have almost fresh water on the surface
throughout, and almost pure salt water near the
bed.
Figure 3.3 – Partially mixed estuary.
In partially mixed estuaries current velocities
near the bed are large, producing turbulence
and thus mixing of the water column. The mixing
is a two-way process: mixing fresher water
downward and salty water upward. The salt
intrusion is now a much more dynamic feature.
During flood, the surface water travels faster up
the estuary than the near bed water. Therefore
the salinity difference between bed en surface is
minimised. Turbulent mixing will be dominant
here. During ebb entrainment will be dominant
as the fresher water is carried over the salty near
bottom water, which cause stratification. This
process is the so called tidal straining.
Turbulent mixing is active throughout the water
column in well mixed estuaries. Yet, there can be
lateral differences across the estuary in mean
flow velocity and salinity. The currents on one
side of the channel can be flood-dominated,
while those at the other side are ebbdominated.
Figure 3.4 – Well mixed estuary.
29
3.2 Sediment transport and morphology
The Rotterdam harbours and waterways are part of the Rhine-Meuse estuary as was described
before. The river transports sediment to the Rotterdam area. Also from the ocean side sediment
particles are transported to the system. To understand the siltation problem better is good to have
some background knowledge on sediment and its transport. Changes in the morphology are
consequences of gradients in net sediment transport rates. The interaction between water and
sediment is very complex an poorly understood.
3.2.1
Sediment properties
Depending on particle size a distinction can be made between silt and clay, sand, gravel and cobbles.
Clay particles are small and have therefore a large surface area compared to their volume. This
chemically active area leads to cohesive characteristics. Sand on the contrary does not stick together
and thus is called non-cohesive. There is no clear boundary between cohesive sediments and noncohesive sediments. The definition is usually site specific. According Wentworth (Figure 3.5)
sediment particles below ±60 µm can be classified as mud. Mud can be further classified as silt or
clay depending on the particle size. Particles between 60 µm and 2 mm are classified as sand and are
clearly non-cohesive. The properties of cohesive sediment are significantly different from the
properties of non-cohesive sediment. Many studies were done on non-cohesive sediment, while on
the contrary less is known about cohesive sediment transport. The shortcomings of most current
cohesive sediment transport models are caused by insufficient description of relevant physical
processes themselves rather than by their numerical implementation.
Figure 3.5 – Sediment classification (Wentworth, 1922).
30
3.2.2
Non-cohesive sediment properties
The first parameter of sediment is actually mentioned already: the grain size. Besides grain size,
other properties (of grain or bulk) are important for the understanding of sediment processes: e.g.
grain density, fall velocity, angle of repose, porosity and concentration. Most of the sand consist of
quartz with a mass density of 2650 kg/m3. The fall velocity depends on the grain characteristics and
the fluid characteristics. In high concentration mixtures, this velocity in reduced by the presence of
other particles. This is the so called hindered settling.
3.2.3
Motion and transport
Incipient motion is important in the study of sediment transport. It is difficult to define precisely at
what flow condition a sediment particle will move, because of its stochastic nature. Sediment is
transported when the shear stress on the grains is large enough. To assess the initiation of motion,
various forces on an individual grain have to be taken into account: drag, lift and gravity. When an
equilibrium is considered, from proportionality the Shield parameter can be derived. From
experiments the Shields curve can be made, which is only valid for non-cohesive sediment and
uniform flow on a flat bed. Despite this fact, Shields is still mentioned because in is used in many
practical sediment transport formulas.
Sediment transport is defined as the movement of sediment through a well-defined plane. The mass
balance contains the transport in both x and y-direction as well as the bed level. Accretion occurs If
the incoming sediment is more than the outgoing sediment, and for the other way around there is
erosion.
There are different transport modes: bed load transport and suspended load transport. The bed load
transport is the transport of sediment in a thin layer just above the bed. Particles that are
transported without contact with the bed contribute to suspended load transport.
Due to the complexity of flow and sediment conditions, engineers should select appropriate formulas
under different flow and sediment conditions. The different methods can give huge differences in
answers.
Figure 3.6 – Sediment transport.
31
3.2.4
Cohesive sediment and fluid mud
Cohesive sediment is a concern in many waterways and is often closely related to water quality
issues. At locations not very much exposed to the influence of waves and current (low energetic
conditions), often a net deposition of mud is observed. Several processes are important when
considering cohesive sediment transport.
Classical transport models focus on the movement of fine particles in the water column. However,
mud can be present in three manifestations:
- suspended in the water column
- aggregated near the bottom
- solid at the bottom
Sediment particles present in the water column settles under the influence of gravity, as the density
of the particles exceeds the water density. The settling velocity vs of a spherical particle can be
calculated from the Stokes-law given the diameter d p , particle density  p , water density  w and
water viscosity
w .
vs


p
  w  gd p2
18w
(Re  1)
(0.1)
An equilibrium concentration profile can be calculated from the balance between downward particle
convection (by settling) and upward particle diffusion (by concentration gradients). When the
cohesive sediment particles collide they tend to aggregate. In the models, aggregation in often
indirectly considered by the change in settling velocity. Small particles form larger flocs by cohesion
(fluculation). The floc structure and the inter-particle forces determine the settling velocity.
However, aggregate growth is enhanced by an increase in particle concentration. Therefore the
settling velocity will also increase with concentration. At higher concentrations, generally near the
bed, hindered settling is observed. This also influences the settling velocity. Several empirical
relationships are found for settling velocity.
As a result of settling, bed deposition occurs. This process is most efficient a low turbulence
intensities, for example during slack tide. After deposition the sediment tends to get more
compacted as it is slowly ‘buried’ by later deposits. This process is also known as consolidation: the
self-weight of the particles expels the pore water and forces the particles closer together. During
consolidation, the particles that were fluid-supported before deposition, become gradually
supported by the grain matrix. An effective stress (difference between total and pore water pressure)
develops. Outflow of water from the bed is an important part of the process. Consolidation continues
until the pore water pressure is the same as the hydrostatic pressure. The time needed for
consolidation strongly depends on the permeability (linear relationship) and the thickness of the
sediment layer (quadratic relationship).
32
Figure 3.7 – Schematic representation of the governing processes between suspension layer and fluid mud layer. A two
layer approach (Winterwerp, 2010).
A fluid mud layer exist in a highly concentrated suspension of fine grained sediment, in which settling
is hindered, but which has not formed an interconnected matrix of bonds, strong enough to
eliminate the potential for mobility. Processes involved in fluid mud transport are schematically
indicated in Figure 3.7. Fluid mud can either be generated by failure of loosely packed cohesive
sediment beds, or by deposition (if the flux of settling particles exceeds the consolidation rate). Fluid
mud of the first form has a concentration close to the original bed concentration, whereas the mud
concentration of the second form has a lower concentration. The typical density of fluid mud is
between 1040 to 1200 kg/m3. The concentrations vary from few tenths to a few hundred g/l.
When fluid mud is left at rest it will consolidate. However when fluid mud is agitated (e.g. by currents
or waves), the consolidation process will slow down. The transport of fluid mud may result in very
high transport rates compared to the water column sediment transport. The sediment concentration
in fluid mud is in the order of a few hundered kg/m3, whereas the concentration in the water column
is in the order of a few tenths kg/m3.
Figure 3.8 – Schematic description of mud transports (Winterwerp & van Kesteren, 2004).
33
3.3 Turbidity maximum
A couple of years ago field measurements were carried out by De Nijs. He studied the process
influencing the siltation in the Botlek Harbour. This section shows the results found by him (De Nijs,
2009 & 2010).
In the first study, it was found that the limit of salt water intrusion indeed existed in the Botlek area.
The turbidity maximum is also more or less located here. The density exchange was found to be the
dominant cause for the transport of suspended particulate matter into the harbour. The survey data
also suggested that the Botlek Harbour basin has a 100% trapping efficiency. Salinity-induced density
gradients control the transport and trapping of sedimentation in the estuary close to the harbour
entrance, the sediment exchange between the estuary and the harbour, and the trapping in the
basin.
Furthermore it was shown that the turbidity maximum is maintained by trapping of fluvial sediment
at the head of the salt wedge. This trapping process is associated with the raining out of fluvial
suspended sediment from the upper fresher part of the water column, into the layer below the
halocline. The baroclinic shear flows and change in mixing characteristic are the dominant
mechanisms. According to De Nijs, the turbidity maximum is independent of bed-based supply of
mud. The freshwater discharge supplies sediment and ensures that the turbidity maximum is
maintained. Relative motion between salt water and suspended particulate matter occurs because of
lags due to re-suspension. Sediment follows complex pathways and the trapping and transport
mechanisms are three-dimensional. To sum up, the salt induced baroclinic and buoyancy structure
keep the fluvial sediment in the estuary through their effects on currents and turbulent damping. The
length of the salt wedge controls the trapping probability of fluvial suspended matter. The amount of
the suspended matter is mainly determined by the length of the salt intrusion and to a lesser extent
by gravitational flow and tidal pumping. Furthermore, de Nijs found that during flood tide saline and
turbid water bifurcate at the junction into the Nieuwe Maas and Oude Maas and are advected back
into the Rotterdam Waterway during ebb tide, but at different phases of the tide. Figure 3.9 shows
patches indicating elevated suspended concentrations advancing and retreating with the head of the
salt wedge on a semi-diurnal timescale.
Figure 3.9 – Lagrangian sketch of harbour siltation under typical hydrodynamic conditions (from: de Nijs).
34
3.4 Reducing costs
As mentioned before, the amount of maintenance dredging has increased since the sixties as the
port expanded and the navigation depth had to be maintained. This can be seen in seen in the figure
below.
Figuur 3-1 – Amount of maintenance dredging in Rotterdam 1918-1986 (MKO, 1987).
The authorities responsible for the dredging, Rijkswaterstaat and Port of Rotterdam, realised that
something must happen as the costs due to maintenance dredging increased. Therefore a project
was launched by both parties to decrease the costs: “Reducing Costs Maintenance Dredging” (in
Dutch: ‘Minimalisering Kosten Onderhoudbaggerwerk’). The main goal of this project was to come up
with concrete solutions to decrease the maintenance dredging costs. The costs were calculated as
follows:
K=QxPxF
K
Q
P
F
=
=
=
=
costs maintenance dredging in a year
the yearly siltation amount in tons
effort needed to remove, transport and store 1 ton of sediment
price for this effort
By use of this formula, there are three sub goals:
Increase the insight in siltation in order to come with concrete proposals to decrease the
sedimentation.
Increase the insight with respect to the most efficient ways to remove, transport and store
sediment.
Increase insight in cost factors in order to pay as less as possible for the efforts.
35
3.5 Measures applied in the past
Although the MKO-projects date from a time when even less was known about siltation, some good
results were achieved. For example: a more effective approach for dredging processes, lower
dredging prices due to the market approach, better exchange of equipment, transparency and much
more achievements. However the main purpose was to devise concrete solutions to solve the
siltation problem.
3.5.1
Siltation trap
The siltation trap was designed to trap the sediment as much as possible at one location. The
advantage was that silt was not heavily spread out in the region, but instead concentrated at the
location of the trap. As a result, siltation in the hinterland area is minimised. A silt trap leads to a
smaller sailing distance for the dredgers. Also the dredging conditions turned out to be much better.
Furthermore, a better distribution of dredging capacity all over the year can be achieved.
As can be seen in Figure 3.10, the siltation trap was located at the entrance of the
Europoort/Maasvlakte I. This trap had a depth of 2 meter below the bed level and a capacity of
3000000 m3.
Also in the central channel in the Botlek a siltation trap was designed (Figure 3.11). Theoretically not
much was known about the trapping of sediment over here. However, also here it was noticed that
the dredging activities were more efficient.
Figure 3.10 – Siltation trap at entrance Europoort/Maasvlakte.
36
Figure 3.11 – Siltation trap at the Botlek entrance.
3.5.2
Silt screen
According to the MKO project team, there were three concrete solutions to keep the sediment out of
the harbour: a water screen, a pneumatic screen or a closed screen. Early studies showed that the
water screen was not feasible. The pneumatic screen seemed to be a viable solution to keep the
sediment out. However from calculations it appeared that lot of energy was needed to supply the
needed air discharge. The current maintenance dredging approach would be more cost effective
than this solution.
The closed screen remained as the last concrete option. The most important requirement was that it
should not hinder the shipping. Based on the criteria chance of success, reliability, strength, repair
costs and payback several options were selected out of dozens. Initially, most attention was paid to
the horizontal movable screen that could slide over a rail. However this option was left out as the
ship anchors could damage the rail, which would mean that the screen is not movable anymore.
Another requirement was added: the screen should consist of pieces which would suffer least
possible damage due to the anchors. Also, the propeller of the ship should not be damaged. This
resulted in a ‘patchwork’ principle. A flexible silt screen was placed in the Botlek as an experiment
(Figure 3.11 for the exact location). Unfortunately, the interaction between the propeller and the
screen was so intense that many repairs had to be made. So also this solution was not the right one.
The movable screen was again investigated, but this time it was made movable in the vertical
direction. To gain insight in the frequency of damage, first a very low screen of two meter was built
over a width of 4.5 m (see Figure 3.12 for the placement and Figure 3.13 for the design). Apparently
this did not function well since there is no silt screen in the Botlek area at present.
Furthermore an underwater dam is still there, near the Botlek entrance. The idea was to make the
entrance narrower and thus reducing siltation.
37
Figure 3.12 – Placement of the test silt screen.
Figure 3.13 – Design low silt screen.
38
3.6 Minimising harbour siltation
3.6.1
Strategies
All over the world authorities tried and are still trying to solve the sedimentation problem. The
current knowledge is insufficient to apply sediment reducing measures optimally. The low number of
applications in practice makes it even harder. Therefore a lot of research was done by Svašek, SRE,
Deltares and HKV for example, to gain insight in the problem and to finally come with concrete
solutions.
A PIANC working group also studied the siltation problem for a long time. They classified all proposed
solutions in different categories, each presenting a strategy. The successful methods according PIANC
can be classified in six groups:
Keep Sediment Moving & mainly passive
Keep Sediment Moving & passive
Keep Sediment Moving & active
Keep Sediment Out & active
Keep Sediment Out & passive
Keep Sediment Navigable & passive/active
Some methods are well-established and widely applied, while other methods are less established and
need further elaboration.
3.6.2
Exchange mechanisms
Several mechanisms can induce an exchange of matter between a river/channel and a harbour basin.
Three main flow mechanisms can be distinguished (Langendoen, 1992):
-
Turbulent exchange
Exchange due to velocity difference between river and harbour flow.
Tidal filling
Exchange due to net flow through the harbour entrance.
Density currents
Exchange flow driven by a density difference between the river water and the water in the
harbour.
It is important to describe the exchange flows as there is a relationship between the mechanisms and
harbour siltation. In some ports one, or more mechanisms can be dominant, while in other ports all
of the mechanisms play a significant role. There are other mechanisms that produce exchange, for
example wind and shipping. However these mechanism play are less important compared to the
three main mechanisms.
39
3.6.2.1
Turbulent exchange
This type of mechanism exist mainly at harbours that are located at rivers. Since the current
velocities in the river are higher than relative calm harbour basis, a mixing layer originates between
the river and the harbour (Figure 3.14). In this layer mass and momentum is being transferred
between the basin and the river. In the upstream corner wave-like disturbances, turbulent vortexes
(eddies) are developed and grow further in the downstream direction. Following the conservation of
mass, the separating streamline at the upstream corner of the harbour entrance is directed in the
harbour. This is true if the assumption is made that the river current is constant outside the mixing
layer and higher than the velocity in the mixing layer. This is generally the case. The water in the
mixing layer flows partly into the river and partly into the harbour at the stagnation point. The
amount of river and harbour water that is entrained, determines the location of the stagnation point.
Higher entrainment, results in a wider mixing layer and the location of the stagnation point further
into the harbour. The geometry of the harbour is also a very important factor.
The entrainment of harbour water into the mixing zone and the supply of water the other way
around at the downstream side wall, causes a circulating flow. These flows, the so called eddies can
be seen in Figure 3.15. The existence of the eddies is also the reason why generated vortexes enter
the mixing zone. Depending on the harbour geometry one primary or more secondary eddies can
occur.
The mixing layer and the eddies are both important phenomena for the transport of matter from the
river to the basin and in the basin itself. Entrainment processes take care of the exchange of matter
between the river and harbour. The eddies (especially the secondary) cause siltation in the centre as
the water velocities are small there. To decrease the exchange, the development and intensity of the
vortexes must be limited.
Several formulas have been developed to calculate the silt flux through a harbour entrance. However
there is an uncertainty in the answer as it involves an exchange coefficient which is hard to
determine a priori. According the formulas the siltation can be reduced by lessening the cross area,
lowering the exchange coefficient, lowering the river velocity or lowering the river sediment
concentration.
Figure 3.14 – The mixing layer in the harbour entrance.
40
Figure 3.15 – Horizontal entrainment mechanism.
3.6.2.2
Tidal filling
Due to variations in water level at the river, a net flow through the entrance can occur. This can also
be caused by withdrawal or discharge of water from/to the basin. The most common cause of net
flow through the entrance is the water level variation due to tide. The filling of the basin occurs
during flood when the water level increases, while during ebb the decrease of water level results in
emptying (Figure 3.16). The one-dimensional shallow water equations can be used to compute the
tidal motion in a harbour.
Continuity
B
 Q

0
t x
(0.2)
Momentum
Q   Q 2 

g QQ
 
 2
0
  gA
t x  A 
x C AR
(0.3)
Here  is the water level, Q is the flow rate, A the harbour cross section, x the direction parallel to
the harbour axis, g gravitational acceleration, C Chézy coefficient and R the hydraulic radius.
Equation (0.3) can be simplified to  / x  0 at the back wall of the harbour. Usually this
approximation can be applied for the entire harbour. The flow rate through the entrance can be
estimated by:
Qs  Ah

t
(0.4)
41
Here Ah is the storage are of the harbour. The incoming water has a higher concentration sediment
than the outgoing water. Therefore silt remains in the harbour basin. The left silt can be estimated
by:
M   Qin cr dt
(0.5)
In this formula M is the mass of the left silt, Qin is the incoming discharge while cr represents the
sediment concentration in the river. The assumption here is that all incoming silt settles. However in
reality there is also an outgoing sediment flux. In the Botlek Harbour almost all of the sediment is
trapped. Therefore the outgoing flow has very little sediment.
Figure 3.16 – Tidal filling and emptying.
3.6.2.3
Density currents
Density currents are caused by density differences in the water. These differences can be associated
with differences in salinity, temperature, silt content, or a combination of course. However salinity
plays the most important role in a lot of harbours, especially the harbours in an estuarine
environment. Depending on the type of estuary, different flow mechanisms can occur. In a salt
wedge estuary there is strong stratification and thus high and sharp density gradients. Typically in
this kind of estuaries, entrainment is the most dominant process. In well mixed estuaries on the
contrary, turbulent mixing plays the most important role. Well mixed estuary have both mechanisms
than can be dominant depending on the tide. During flood, turbulent mixing will be dominant, while
during ebb entrainment will dominate.
If the channel in front of the harbour is constant of density, the water in the harbour basin will
approach this density. In time the density difference between the two water bodies decrease, which
on turn means that the exchange discharge decreases. However, the densities in the harbour and
channel are not constant, both in time and space. In estuarine systems, the cannel density changes
all the time as a consequence of the tide. Because of this the direction of the density-driven
exchange flow can continually reverse in the harbour entrance.
42
The salinity of the water influences siltation of the channels and harbour basins as it has a large
effect on the flocculation of silt. The flocculation affects the fall velocity of the particles. Harbours
situated on estuaries at the transition fresh-salt water have to deal with large problems when it
comes to siltation.
3.6.2.4
Estimation silt-flux
As already was mentioned the rate of exchange Q between the river and harbour basin is governed
by a number of potential exchange flow processes: horizontal entrainment Qe , tidal filling Qt and
density current. The density current can be subdivided in the saline driven density current Qd , the
temperature driven density current QT and the sediment-induced density current Qs .
Harbour basin siltation rates can be computed by the zero-method approach (Eysink, 1989). This
method is based on the mass balance equation. If we denote the surface area by S and the depth by
h , the harbour volume V is S  h . The averaged suspended sediment concentration in the harbour
basin is ch , while that of the river is ca (here the subscript stands for ambient). The concentration in
the river may vary with time but with another time scale than the harbour concentration. Because of
this it is treated as a constant.
Figure 3.17 – Sketch exchange harbour basin – river.
Although the processes are very complex, an estimation can be made on the amount of silt that goes
through the entrance (Van Schijndel and Kranenburg, 1998).
F   cvdA
(0.6)
A
With F as the silt-flux, c( x, y, z, t ) the local concentration, v( x, y, z, t ) local speed perpendicular on
the entrance and A cross-sectional area. The formula can be simplified.
F  kur  ca  ch  A
(0.7)
43
Here ca and ch are the mean silt concentration in the channel and harbour. The channel velocity is
given by ur , while k is the exchange coefficient. In case of only horizontal entrainment, the
exchange discharge can be described by the next formula (Booij, 1986 and Winterwerp 2005).
Qe  kAur
(0.8)
This exchange coefficient contains many physical processes (e.g. the harbour geometry) and cannot
be determined à priori. Booij and Winterwerp both give a range in the order of 0.02 to 0.05. Because
of the uncertainty in the coefficient the silt flux formula is not that accurate. However from the
formula, one can see how to decrease the flux. According the formula, harbour siltation can be
reduced by decreasing A , k , ur or ca .
The siltation rate can be estimated by the following below, where p is the basin trapping efficiency.
According de Nijs the trapping efficiency is nearly 100% in the Botlek Harbour (De Nijs, 2008)
Siltation rate  p  Q  ca
3.6.2.5
(0.9)
Interaction of mechanisms
It is important to investigate which mechanisms are responsible for a given flow pattern, in order to
find out how to influence the flow. The water exchange between the channel and the harbour can be
caused by one or a combination of the exchange mechanisms. In some harbours one can be
dominant over the other. Sometimes one or more main mechanism(s) can even be neglected, while a
normally less important mechanism can sudden be very important. For example, a harbours that is
located directly on the sea coast the exchange flow due salinity differences is low. River harbours
that are situated landwards have little tidal filling/emptying. Estuarine harbours are often
determined by a combination of all flow mechanisms. Generally when the flow mechanisms coincide,
the largest exchange flow is given by the density current mechanism. Sometime the assumption is
made that the flow rate through the basin entrance is the sum of the rates due to the three
mechanism separately. However this is not really accurate as there is interaction between the
mechanisms (Booij, 1986). More studies were made in the past to study the interaction. It turned out
that the eddy in the entrance can be supressed/hindered by the density driven flow. If an eddy and
density flow occur together, the eddy will cause mixing between the upper and lower layer, which on
turn reduce the density driven exchange flow (Dursthoff, 1970). Another effect of the eddy is found
by Christiansen (see Figure 3.18). He stated that the an eddy is narrowing the stream filling width,
which results In a higher velocity and thus a larger sediment transport into the basin. The sediment is
deposited further in the basin because of lower velocities. During ebb the eddy is pushed out by the
emptying. The flow width is now larger, the velocity lower and thus not sufficient to re-suspend all
the deposited sediment (Christiansen, 1987). Several measures can be made to reduce the water
exchange. Generally the exchange is reduced by decreasing the cross-section, depth, river velocity
44
(however this can even increase channel siltation), increasing the length-width ration of the harbour,
or decreasing the density difference.
Figure 3.18 – Currents in a tidal harbour a) ebb, b) flood.
Figure 3.19 – Schematisation the components and the combinations of the three.
45
3.6.3
Possible solutions
In this section possible solutions found in literature to cope with harbour siltation, are summed up.
3.6.3.1
Narrowing harbour entrance
The silt flux formula already showed that reducing the cross sectional area of the harbour entrance is
an effective measure to limit siltation. Because of the reduction, the length of the mixing layer will be
shortened so that less mixing will occur.
Advantages
+ Simple construction.
Disadvantages
- Shipping experiences it as nuisance.
+ Effectiveness can be estimated pretty well.
+ No mechanical parts that require much
maintenance.
Table 3-1 – Narrowing harbour entrance. Advantages and disadvantages.
3.6.3.2
Pile groynes
The use of pile groynes upstream of the harbour is a possibility to reduce the turbulent exchange.
The poles broaden the mixing layer and therefore transition of current velocities is gradual. As water
exchange between river and basin reduces, less sediment is transported to the harbour basin. The
working of the poles can be influenced by the distance between the poles.
Figure 3.20 – Row of poles and the corresponding velocity profile.
Advantages
Disadvantages
+ Simple construction.
- In small rivers not applicable, due to shipping
hindrance.
+ Effectiveness is proved in a laboratory.
- Permeability can be reduced by floating
debris.
maintenance.
+ Relative cheap.
+ Preventing of strong eddies.
Table 3-2 – Row of poles. Advantages and disadvantages.
46
3.6.3.3
Current deflecting wall
The Current Deflecting Wall is a wall that influences the water flow by deflection (see Figure 3.21).
There is a distinction between a classical CDW and a S-curved wall, with or without a sill. By applying
the classical CDW, the flow is initiated more into the harbour so that the birth of an eddy is
counteracted. The S-curved type on the other hand, initiates the flow out of the harbour. Therefore
the eddy and the mixing layer, where lot of the siltation takes places, is moved more out of the
harbour basin. High concentrations near the bed are also pushed out of the basin by the sill(s). Due
to the presence of the sill, water from the upper part of the water column will fill the basin during
flood. This water contains less sediment.
Figure 3.21 – Current deflecting wall with sills.
Figure 3.22 – Flow pattern. Without and with CDW.
Advantages
+ Shipping little effected by construction.
+ Effectiveness is proved in a laboratory.
Disadvantages
- Effectiveness hard to estimate. A
comprehensive optimisation study must be
performed. This can be quite expensive.
- Construction very expensive. Especially for
major harbours.
maintenance.
+ Can withstand high velocities.
Table 3-3 – CDW. Advantages and disadvantages.
47
3.6.3.4
Sill
Just as narrowing the harbour entrance in horizontal direction, the cross section can be reduced by
applying a sill. The sill can be movable or static.
Advantages
+ Bottom transport blocked.
Disadvantages
- Construction under water. Maintenance is
hard.
- Possible hindrance for shipping.
- Construction and/or ship anchors and
propellers can be damaged.
- Incoming sediment cannot go out during ebb.
Table 3-4 – Sill. Advantages and disadvantages.
3.6.3.5
Siltation trap
A siltation trap (Figure 3.23) catches the entrained bottom transport from the river, as well part of
the fine sand that is carried in suspension. Much of the sediment is trapped in the silt trap and
cannot enter the basin anymore. To remain effective, the silt trap must be maintained at depth. In
addition, the trap should be constructed far enough from the bank, so that the stability of the bank is
not in danger. The idea behind the silt trap is that the sediment is concentrated at one location
instead of being spread out. This is an advantage for the dredging process.
Figure 3.23 – Silt trap.
Advantages
+ A simple and cheap measure.
Disadvantages
- Depth must be maintained.
+ No shipping hindrance.
- If designed wrongly, it can trap more sediment
than without the silt trap.
- Only for coarse sediment.
+ Sediment more or less concentrated at one or
several locations.
+ Easier to dredge.
Table 3-5 – Silt trap. Advantages and disadvantages.
48
3.6.3.6
Eggs of Thijsse
The eggs of Thijsse are more or less egg-shaped entrances where an eddy occurs. This results in that
the sedimentation takes place in the middle, outside the fairways. Thus in fact this is a controlled
trap, just similar to the silt trap.
Figure 3.24 – Egss of Thijsse.
Advantages
Disadvantages
+ No shipping hindrance.
- Construction puts a claim on the available
space. At harbour entrances there is often not
enough space available.
- Only effective in dynamic water systems.
+ Sediment more or less concentrated at one
location.
- Dredging is still necessary.
Table 3-6 – Egss of Thijsse. Advantages and disadvantages.
3.6.3.7
Pneumatic barrier
A pneumatic barrier is used to counter exchange of substances/water at a certain interface. Using a
compressor, air is blown into the water. The screen/barrier generates an upward flow, as can be seen
in Figure 3.25. Most of the water is discharged near the surface, also through the formed eddies.
However there are different opinions on whether this screen will reduce sedimentation.
Figure 3.25 – Pneumatic barrier.
Advantages
+ No physical barrier.
Disadvantages
Mechanical parts that require periodic
maintenance.
- Energy and thus also the costs are high.
- Vessels are hindered because of the flows.
Table 3-7 – Pneumatic barrier. Advantages and disadvantages.
49
4 DREDGE DATA ANALYSIS
The dredge data analysis might give some insight in the siltation problem. Data from 1995 to 2010 for
the Botlek Area was provided by the Port of Rotterdam and can be found at page 130. The
corresponding graph, showing the total annual dredging was already shown at the end of section 1.1.
The total dredged m3 in the area in the particular period fluctuates between 1.2 and 2.5 million m 3.
The data that was provided (page 130) is divided in the so called “dredging domains” (Dutch:
“baggervakken”). By dividing the amount of m3 per domain we obtain the figure below. As expected,
the rates are the highest at the silt trap. The mouth of the Botlek show also very high rates.
3
2
Figure 4.1 – Dredged m per m a year. According data from 1995-2010. (Databaste PoR, 2011).
50
Also the dredge costs per domain were provided by the Port of Rotterdam. For the Botlek Harbour
only the dredge cost are estimated to be 3 million Euro a year. If these costs are divided by the
amount dredged material, we obtain the dredging costs for 1 cubic meter. From Figure 4.2 we can
conculde that:
- The further away from sea, the higher the dredging costs.
- The harder it is to manoeuvre, the higher the dredging costs.
3
Figure 4.2 – Costs per m . According data from 2010. (Database PoR, 2011).
51
5 RESEARCH STRATEGIES AND APPROACH
5.1 Strategies
There are many ways to tackle the siltation problems. However, such a complicated subject should
be narrowed down to a study on a smaller part. In this thesis the focus is more on the understanding
of the flow patterns and the ways to influence them positively. The use of models will be a good tool
to have more insight in the problem. Also they are used to examine certain proposed solutions.
5.2 Use of models
Estuarine flows are in practice very complex and hard to predict. Models can be used to understand
the relevant processes. Some models can even be used to estimate quantities like siltation.
Fundamental equations in estuarine models are the mass, momentum and sediment continuity. In
practice approximations are needed to solve the equations. Either tidal averaged or conditions
within-tide can be modelled.
A 3D model is required in estuarine environments. They represent fully the vertical and horizontal
profiles of velocity, density and sediment concentration. As computer power increases, 3D models
are becoming less costly to run. However, a model needs sufficient reliable data to calibrate and
validate them. Field data or the use of a physical scale model can really help to apply and validate the
3D model (Figure 5.1). Models are not only restricted by field (or scale model) data, but also on
computer resources. The larger the model, the more dimensions, the finer the grid the more depth
layers, the longer it takes for a computer to run a simulation. The art is to find a suitable comprise
between good results and fast computation. Each assumption must be kept in mind while
interpreting the results.
Figure 5.1 – Model validation and calibration.
52
53
6 HYDRODYNAMICAL MODELS
6.1 Software
Currently the Port of Rotterdam uses the hydrodynamical flow model OSR to estimate water levels,
flows and other parameters. OSR uses a combination of the software SIMONA and Delft3D to
determine the hydrodynamics and to estimate the morphological changes.
SIMONA which stands for ‘Simulation Models Wet’ when translated, is a collection of mathematical
models that describe the hydrodynamic processes. The four models within SIMONA are:
- WAQUA: For the simulation of water movement en transport of suspended material (2D)
- TRIWAQ: For the simulation of water movement en transport of suspended material (3D)
- SIMPAR: For the simulation of particles in water
- SLIB3D: For the simulation of silt transport in water
This software package is developed for Rijkswaterstaat and can only be used with their permission. It
is neither a commercial software nor an open source one.
Delft3D can do even more than SIMONA. The D3D-FLOW module is used to compute water
movements while D3D-SED is used for morphological calculations. One of the differences between
Delft3D and SIMONA is that D3D is open source an can be used by everybody. However a
disadvantage of this programme compared to SIMONA is that it is not able to perform parallel
computing (D3D version 4.0). This makes the computation time extremely long.
Looking only at the hydrodynamics , there are three options:
- SIMONA
- D3D-FLOW
- SIMONA + D3D-Flow
When
-
including sediment in the model, there are six options. The use of:
SIMONA
SIMONA + D3D-SED
SIMONA + D3D-FLOW + D3D-SED
SIMONA + D3D-FlOW (inclusive sediment)
D3D-FLOW + D3D-SED
D3D-FlOW (inclusive sediment)
Each option had its advantages and disadvantages. Depending on the type of problem one option can
be preferred over the other. For this study a combination of SIMONA and Delft3D-FLOW will be used.
Why this option is chosen, will be described further on in this chapter.
54
6.2 Model equations and assumptions
The equations which are solved in SIMONA and Delft3D are mathematical descriptions of physical
conservation laws for:
- Water volume (continuity equation)
- Momentum
- Tracer Mass (transport equation)
- Salinity
The assumptions that are used in Delft3D can be found on page 132.
6.3 Available models
Two Delft3D models are used by the Port of Rotterdam:
- Coarse Model
- Fine Model (grid refinement of 3 times)
The input for these two models are provided by the SIMONA simulations, which cover a larger part of
the system (Figure 6.1) The quality of the models were judged by the external engineering company
Svašek. They found that the prediction of water levels and salinity were quite good (HydroMeteo,
2011). In addition the quality can be checked permanently by comparing the measurements with
predictions (on the website http://www.mx-systems.nl/osr).
Figure 6.1 – SIMONA and D3D model.
55
It must be noted that the resolution is not the only difference between the two models. Also the
river and sea boundaries are located elsewhere. Most of the time the coarse model is used by the
Port of Rotterdam as it runs much faster.
Botlek Area
Fine
Coarse
Total Area
Table 6-1 – Coarse and Fine model.
The fine model is three times finer compared to the coarse model. This means that there are
approximately 32 = 9 times more cells in the fine model. The coarse model has 10 layers, whereas
the fine model has 7 layers.
Generally in estuarine systems at least 10 layers have to be defined. However it is strongly advisable
to model with 20 layers. Despite the long calculation time, this resolution is necessary to determine
the salt intrusion and the circulation in the mouth of the Botlek Harbour. The coarse model is too
coarse and therefore not acceptable. The fine model should be good enough, but with 20 layers the
amount of cells would be huge. According the Port of Rotterdam modellers this would be too heavy
for a desktop.
A way to solve this problem is to use the large, coarse model, to generate conditions for a smaller
and finer model. This way the resolution in the Botlek Area is still large enough and the computation
time will be decreased.
56
6.4 Adjusted model
6.4.1
Boundaries
Where the small model should be ‘cut’ out of the large model depends mainly on the tidal excursion.
The tidal excursion is the net horizontal distance over which a water particle moves during one tidal
cycle. The small model boundaries should be at least one tidal excursion from the centre of the area
of interest. Roughly speaking there are three paths from the centre of the Botlek mouth as can be
seen in the figure below.
Figure 6.2 – Paths from centre mouth Botlek.
The tidal excursion can be estimated by integrating the flow velocities over time. These average
velocities are taken from ‘Hydro Meteo v3’. For the West-East path measuring station ‘Botlek’ will be
used, while the ‘Botlek bridge’ measuring station provides information to determine the southwards
excursion. According to these figure the following paths are calculated:
Minimal required distance from Botlek to boundaries:
Westward:
at least 19.8 km
Eastward:
at least 8.6 km
Southward:
at least 8.1 km
57
Figure 6.3 – Estimation tidal excursion (W-E).
Figure 6.4 – Estimation tidal excursion (W - SE).
58
The final small model (blue) can be seen in the figure below. The derived distances are multiplied by
approxomately 1.5 to really make sure the model is large enough.
Figure 6.5 – Large and small model.
Distance from Botlek to boundaries:
Westward:
30 km
Eastward:
12 km
Southward:
11 km
59
6.4.2
Hydrodynamical boundary conditions
The tide and river discharge must be defined at the boundaries of the large model. This model, which
will use SIMONA, provides information for the smaller Delft3D model. As can be seen in Figure 6.6,
Riemann time series form the input of the small model.
Figure 6.6 – Boundary conditions large and small model.
6.4.3
Resolution choice
Some choices have to be made when it comes to resolution:
- Spatial Resolution : number of grid cells/layer
- Spatial Resolution: number of layers
- Time Resolution: time step
A trade-off between the required resolution and the computation time must be made.
60
6.4.3.1
Spatial resolution
It has already been mentioned before that the model should contain 20 layers as we are dealing with
an estuarine environment. The coarse model with 10 layers is too coarse, while the fine model
should be good enough. However it is expected that the fine model will take very long to run,
especially because there are already 20 layers. Somewhere in between the trade-off has to be found.
Another option is to use a model which is two times finer instead of three. Or the coarse model can
be used while refining the area of interest: the Botlek Area. Depending on the computation times
(6.4.3.3) and the resolution at the Botlek mouth, a choice will be made.
6.4.3.2
Time step
The choice of time step depends on several requirements. One of the most important requirements
is that it should fulfil the Courant-Friedrichs-Lewy condition. This is a necessary condition for
convergence while solving the partial differential equation numerically.
It must be noted that the CFL condition is a necessary one, but not necessarily sufficient condition for
convergence. There are other conditions which in turn could imply further limitations on the length
of the time step and spatial intervals. However these conditions are not given here. Instead the time
steps which are used by the Port of Rotterdam modellers from experience are used as a basis. A time
step of 0.25 minutes is a good starting point (Hulsen, 2011). Delft3D-FLOW is based on a robust ADI
solver which allow a large time step well beyond the CFL condition. A time step equivalent to a
Courant number up to 10 generally still gives accurate solutions (Deltares, 2007). The Courant
number should not be too high. Furthermore the results (e.g. salinity, circulation) using different
time steps are compared to see if there are major differences.
The CFL condition shows that there is a relationship between the time step and spatial length. A
model which is two times finer, requires a time step which is two times smaller. For example the
model which is 3 times finer, has 9 times more cells. In addition the time step should be three times
smaller which means that the computation time is increased by a factor 27!
6.4.3.3
Computation time
Four models are compared, using different spatial and time resolutions. The aim is to see how the
used desktop performs to have an idea how long the simulations take. The models that are used:
- A: Coarse
- B: Coarse overall and fine local
- C: Fine (two times finer)
- D: Fine (three times fines)
Ten layers are compared with twenty layers and time steps are taken to be 0.05; 0.125; 0.25 and 0.5
minutes. The results of the computation time divided by the modelled time is given at Table 6-2.
61
Model
Number of
layers
10 layers
20 layers
A
B
C
D
Coarse model
Coarse model
Fine model
Fine model
and fine local
2x finer
3x finer
8546 cells/lyr
16201 cells/lyr
34184 cells/lyr
89230 cells/lyr
0.05
0.15
0.23
0.58
1.58
0.125
0.06
0.09
0.33
0.71
0.25
0.03
0.04
0.02
0.44
0.5
Error
Error
Error
Error
0.05
0.33
0.46
1.67
2.30*
0.125
0.12
0.19
0.58
1.00*
0.25
0.07
0.10
0.33
0.56*
0.5
Error
Error
Error
Error
∆t (min)
Table 6-2 – Computation time / simulated time for different combinations. (*Single precision).
The requirements was that 20 layer should be used and furthermore the resolution at the mouth of
the Botlek Harbour should be good enough. Model A is too coarse whereas model D gave errors
when using the default Delft3D double-precision. Model B and C have almost the same resolution at
the mouth of the Botlek Harbour. Model B is three to four times faster than model C, while it should
give almost the same results at the end. Therefore model B with 20 layers will be used in the future
simulations.
Figure 6.7 – Model B: Coarse overall, fine local. Shades show the depth contour (Note: legend scale not fixed).
62
To estimate the simulation time for future simulations the following formula can be used, assuming a
linear relationship between the resolution and computation time.
Simulation time
Number of Cells  Number of Layers

K
Modelled time frame
Time step t  min 
(0.10)
The coefficient K is the performance factor depends on the type of hardware used to simulate the
models. A faster computer will have a lower K value. Also the number of included variables (like
salinity, sediment) influence the computation time as extra equations have to be solved. For
simulations shown at Table 6-2 only the salinity process was turned on within Delft3D.
Figure 6.8 shows indeed that there is a more or less linear relationship between the resolution
(spatial and time combined) and the computation time. For this particular desktop, Intel Quad Core
i7 2600 @ 3.5GHz and 8GB memory, the K-value is 10-7.
Figure 6.8 – Relation resolution - computation time.
63
6.4.3.4
Courant number
The Courant number is important to assess the accuracy of the models. Figure 6.9 shows the Courant
numbers that belong to model B and the time steps of 0.25; 0.125 and 0.05 minutes. From the figure
it can be seen that for time steps of 0.05 and 0.125 minutes, the Courant number is still below 10 as
required (L. Hulsen). For a time step of 0.25 minutes the Courant number in the blue areas is in the
order of 10-20. It is important to compare the time steps when presenting the results, to see
whether this high Courant number forms a real problem.
Figure 6.9 – Courant numbers model B.
64
65
7 DETERMINATION OF CIRCULATIONS
Early in the report it was already mentioned that the siltation problem is the largest in the Botlek
Area. Therefore we focus on the exchange mechanisms between the river and the Botlek Harbour. In
section 3.6.2 the three mechanisms were described. Turbulent exchange (or horizontal entrainment)
and tidal filling contribute to the horizontal circulation, while the density currents contribute to the
vertical circulation.
7.1 Horizontal vs. vertical circulation
At the mouth of the Botlek Harbour the horizontal and vertical circulations are ought to be
determined. The contribution of the horizontal circulation versus the contribution of the vertical
circulation must be compared. Not only to have a general view on the exchange mechanisms, but
also since interventions on horizontal circulation are ‘easier’ to implement. There are almost no
means to counter vertical circulations. In other words interventions are only interesting if the
contribution of the horizontal circulation to the total circulation is relatively large.
7.2 Formulation
A hypothetical cross section of a harbour mouth is shown in the figure below. In reality the width is
much larger than the depth.
Figure 7.1 – Hypothetical cross section harbour mouth.
The width varies with the height while the depth varies over the width. The area of the cross section
can be given by:
A
wmax

0
h( y ) dy 
hmax

b( z ) dz
(0.11)
0
66
The mean velocity in the cross section is:
1
1
u   u( y, z ) dydz 
A A
A
wmax

0
h
w( z )
h( y )


1 max 
  u( y, z ) dz  dy     u( y, z ) dy  dz
A 0  0
 0


(0.12)
The deviation u '' from the mean velocity is:
u ''( y, z )  u( y, z )  u
1
u ''( y, z ) dydz  0
A 
A
with
(0.13)
So far the calculations are trivial. However the determination of the circulation is less trivial as the
terms could be non-linear (velocity-height and velocity-width).
The mean depth and mean width velocity can be defined by:
1
u1 ( y ) 
h( y )
u1  ( z ) 
h( y )
1
b( z )

u( y, z ) dz
(0.14)
0
b( z )

u( y, z ) dy
(0.15)
0
Integration over width and depth respectively returns again the mean cross sectional velocity. The
horizontal and vertical circulation can now be given by:
1
u '( y )  u  u1 ( y )  u 
h( y )
1
u '( z )  u  u1 ( z )  u 
b( z )
h( y )

u( y, z ) dz
(0.16)
0
b( z )
 u( y, z) dy
(0.17)
0
Integration over width and depth respectively should give zero. Because of the absolute values, the
original velocity u ( y, z ) cannot be decomposed as follows:
u( y, z )  u  u '( y )  u '( z )
(0.18)
E ( y , t )  u( y , t )  h ( y , t )
(0.19)
We obtain the discharge as follows:
(Winterwerp, 2011)
67
Figure 7.2 – Horizontal and vertical circulation.
7.3 Cross sections
First of all the cross section river-harbour has to be defined. Since it is not very clear where the
transition from river to harbour is, three cross sections are selected in the mouth (Figure 7.3).
Delft3D is not able to create a velocity field in the vertical plane when defining a cross section.
Therefore observations points are chosen along the cross section. On the contrary these points are
able to show the velocity profile over the vertical. The chosen cross section profiles can be found at
page 134.
Figure 7.3 – The three cross sections and corresponding observation points at the Botlek mouth.
68
7.4 Data handling and script
As there are twenty layers, each observation point gives twenty velocities at the vertical. However,
these velocities are not given at fixed vertical coordinates since sigma-planes were used in the
Delft3D simulations. Therefore the data must be manipulated first in order to use the formulations
described in 7.2. As can be seen on page 138 the sigma-planes will be transformed to z-planes. To
determine the horizontal and vertical circulation in the Botlek mouth, the following steps as shown in
the scheme below have to be taken. The Matlab script that is written can be found on page 140.
Figure 7.4 – Scheme to determine the relative contribution of horizontal and vertical circulation.
69
7.5 Model input
7.5.1
SIMONA
Boundary
conditions
Tide
River discharge
‘Average’
‘Average’
2300 m3/s
Table 7-1 – SIMONA Boundary conditions (provided by the Port of Rotterdam).
7.5.2
Delft-3D
Simulation
number
Sim 1
Sim 3
Sim 5
Sim 2
Sim 4
Sim 6
Processes
Time step (min)
None
None
None
Salinity
Salinity
Salinity
0.050
0.125
0.250
0.050
0.125
0.250
Table 7-2 – Simulations with and without salinity at different time steps.
Other parameters
Timeframe
Gravity
Fresh water density
Temperature*
Roughness
Initial water level
Initial salinity*
Horizontal eddy viscosity
Horizontal eddy diffusivity*
Vertical eddy viscosity
Vertical eddy diffusivity*
Turbulence model
Three weeks
9.81 m/s2
1000 kg/m3
15 ⁰C
0.024
0m
31 ppt
1 m2/s
10 m2/s
0 m2/s
0 m2/s
K-ε
Table 7-3 – Delft3D Parameters (* only required if salinity is turned on).
70
7.6 First results
7.6.1
Comparison – water level
To judge whether the choices of time step and time frame are good enough, the models must be
compared. Only water levels at observation points ´Botlek 3´ and `Maasmond´ are shown in the
figure below. However more locations were analysed. The locations of all the observation points can
be found in the Appendix at page 148.
The figures show clearly that the water levels differ for saline or fresh water. Another conclusion that
can be drawn is that there is barely no difference between a time step of 0.125 or 0.25 minutes when
it comes to water level. Furthermore, it can be seen that the initial water level of 0 m was a good
choice as the spin-up time is very low. The time frame of three weeks was thus not necessary when
considered water levels only. However, the salinities must also be analysed to find whether the initial
condition of 31 ppt was good enough and whether the time frame was long enough.
Water level first two days
Zoomed in
Table 7-4 – Comparing different time steps.
71
7.6.2
Comparison – salinity
The figures below illustrate again the results at only two locations. Despite the higher Courant
number, also here it can be seen that the time step choice of 0.25 min is just as good as 0.125 min.
For both locations however, the initial condition of 31 ppt not a very good choice. For ´Botlek 3´, the
salinity decreases to about 1 ppt, while the salinity at ´Maasmond´ fluctuates around 25 ppt. In the
Maasmond the tidal influence is much larger than for example at the Botlek; which makes sense.
A badly chosen initial condition results in a larger ´warming-up time´ of the model. To decrease this
time a so called ´initial-field´ will be created for future simulations. The spatially varying values of
water level and salinity at the end of the old simulations will form the initial field for the new
simulations. The time frame can be reduced from three week to one week for example. This is done
for the simulations with time step 0.05 minutes and for future simulations. Again these simulations
have almost the same results as the ones with the higher time steps. The results for time step 0.05
minutes are now shown here below. Since the three time steps give almost the same results a higher
time step of 0.5 minutes was tried out as well. However the simulation terminated after a very short
time, which may indicate that the time step is too large for convergence and stability.
Salinity. Three weeks.
Zoomed in
Table 7-5 – Comparing different time steps and analysing the spin-up time.
72
7.6.3
Initial field
An initial field was created using the values shown in the table below. The water levels and velocities
are taken to be zero, while the salinity differs locally. Since the goal is to shorten the spin-up time, it
is enough to take a rough estimate for the initial values. After a couple of time steps the values
approach the reality. The spatial field (Figure 7.5) is created by interpolating the values of Table 7-6.
Location
Noordzee 1
Noordzee 2
Maasmond
Calandkanaal
Nieuwe Waterweg
Scheur
Mississipihaven
Hartelkanaal 1
Hartelkanaal 2
Oude Maas
Botlek 1-7
Maashaven
Waalhaven
Nieuwe Maas 1
Nieuwe Maas 2
ppt
28.5
27.7
25
20
8
0.6
19.5
5
0.65
0.6
0.5
0.35
0.35
0.45
0.45
Table 7-6 – Initial values at several locations.
Figure 7.5 – Initial salinity field (in ppt’s).
73
7.6.4
Comparison with measurements– flow velocities
Althoug the model is well validated by Svašek, it is good to compare the results with measurements.
The computed flow velocities are compared with measured velocities which can be found at the
stream atlas (Stroomatlas Benedenrivieren en aanlopen, 1992). This atlas shows flow velocities of the
upper layer of the water column for average conditions. The comparison can be found in the
Appendix at page 150. Note that the flow velocities of the stream atlas is given in knots (1 knot ≈
0.514 m/s). The results show more or less the same characteristics.
7.6.5
Flow pattern
In the following figures the flow pattern at the mouth of the Botlek is given.
-6 H w.r.t. HW Botlek
River flow westward
Little inflow westside of mouth
74
River flow westward
Neglactible inflow westside of mouth
River flow westward
75
River flow westward (weakened)
Tide and river discharge “meet”
Inflow westside of mouth
NeglactibleLittle outflow eastside of mouth
Start forming of an eddy on the basinside at the west
76
River flow eastward
Inflow westside-middle of mouth
Eddy on the basinside at the west
HW Botlek
River flow eastward
Little outflow westside and little inflow easside of mouth
Eddy basisside on the west of mouth weakened
Eddy in middle of mouth
Figure 7.12 – Flow pattern at HW Botlek.
77
+1 H w.r.t. HW Botlek
River flow eastward
Neglectible outflow westside of mouth
Eddy basisside on the west of mouth dissappeared
Eddy in middle of mouth toward east and weakened
River flow eastward
Little outflow westside of mouth
Eddy eastside mouth almost dissappeared
78
Outflow westside mouth
Inflow eastside mouth
Generation of an eddy riverside of mouth
River flow westward
Little outflow westside of mouth
79
River flow westward
Neglectible outflow westside of mouth
River flow westward
Neglectible inflow westside of mouth
80
7.6.6
Horizontal circulation – qualitative
As can be seen in the previous figures, turbulent exchange between the river and harbour cause
vortexes. These eddies play an important role in the exchange of mass and momentum and this in
the exchange of sediment. Figure 7.19 shows clearly the existence of such a vortex at the Botlek
mouth. The Appendix at page 186 shows the horizontal flow patterns at the Botlek mouth, for the
top, middle and bottom layer.
Figure 7.19 – Vortex at the Botlek mouth.
81
7.6.7
Circulation – quantitative
Below are the circulation results of cross section A averaged over cross section and several tides.
Simulation
number
Fresh /
Saline
Time step
min
1
3
5
2
4
6
Fresh
Fresh
Fresh
Saline
Saline
Saline
0.050
0.125
0.250
0.050
0.125
0.250
Horizontal circulation
tidally averaged
cross sectional averaged
0.043 m/s
0.044 m/s
0.044 m/s
0.043 m/s
0.044 m/s
0.044 m/s
Vertical circulation
tidally averaged
cross sectional averaged
0.012 m/s
0.013 m/s
0.013 m/s
0.014 m/s
0.015 m/s
0.015 m/s
Table 7-7 – Average circulation at cross section A.
As was concluded before, the time step in this range does not influence the final result much. The
horizontal average circulation is the more or less the same for fresh and saline water. On the other
hand, the vertical circulation increases with approximately 10 to 20 % when including salinity. This is
because an estuarine environment exists where due to salinity differences, stratified flow occurs.
Table 7-8 shows some value differences of the three selected cross sections. In fact this is not really
a problem as the goal is find ratio of the horizontal and vertical circulations. The ratio is about 80:20
to 90:10 for fresh water and changes to 75:25 to 85:15 for saline water.
As was stated before, measures to counteract the horizontal circulation are much more effective
compared to measures against vertical circulation. The horizontal circulation is dominant for this
‘average’ case with average tide and average discharge.
Simulation
number
Cross
Section
Fresh /
Saline
1
1
1
2
2
2
A
B
C
A
B
C
Fresh
Fresh
Fresh
Saline
Saline
Saline
Horizontal
circulation
tidally averaged
and
cross sectional
averaged
0.043 m/s
0.046 m/s
0.043 m/s
0.043 m/s
0.045 m/s
0.040 m/s
Vertical
circulation
tidally averaged
and
cross sectional
averaged
0.012 m/s
0.011 m/s
0.006 m/s
0.014 m/s
0.014 m/s
0.008 m/s
Horizontal
Circulation
/ Total
circulation
Vertical
Circulation
/ Total
circulation
78 %
81 %
88 %
75 %
76 %
84 %
22 %
19 %
12 %
25 %
24 %
16 %
Table 7-8 – Average circulation at the three cross sections using lowest time step.
82
83
8 CONTRIBUTION EXCHANGE MECHANISMS
8.1 Decomposition method
In Chapter 7 the formulas to decompose into the horizontal and vertical circulation were given. This
decomposition was easier to implement in the script. However there was a need to decompose in
three components as described in 3.6.2: turbulent exchange, tidal filling and density currents. Those
three components provide more information than just the contribution of the horizontal and vertical
circulation. The script was improved, and from now on the contribution of the three components are
given.
Figure 8.1 – From two to three components.
8.2 Contribution of the three mechanisms
Cyclic boundary conditions were used in the model, so when looking at the results there are no
differences in tides (assuming the spin-up has died out). It is sufficient to just show one tide. To be
sure that the model has “warmed up”, a tide somewhere at the end of the three week simulation will
be taken (Figure 8.2). In the figure underneath it we can see the discharge (or the velocity when
divided by the cross sectional area) through cross section B. Looking at the figure it is expected that
tidal storage is dominant.
The contribution of the three mechanisms in shown for the three cross sections as described at 7.3.
Initially figures were made using the cross sectional velocities. However later on we might have
measures which will change the cross sectional area. The results before and after the measure
cannot be compared then, and therefore discharges are presented instead of velocities. A full tide of
approximately 12½ hours is taken. In the horizontal axis of the figure we can read the plotting time
step (do not confuse with the numerical time step). The time step is 5 minutes, with 150 steps we
have 750 minutes or 12½ hours.
84
Water level
Figure 8.2 – Water level of a tide according the model (from LW Botlek to LW Botlek).
Discharge (velocity)
Figure 8.3 – Discharge through cross section B according the model (from LW Botlek to LW Botlek). Positive is harbour
outflow, negative is harbour inflow.
85
Cross section A
Distribution Components over time (Cross Section A)
2.5
3
Absolute cell averaged discharge (m /s)
8.2.1
Density Currents
Horizontal Exchange
Tidal Filling
2
1.5
1
0.5
0
0
50
100
Timestep (with dt = 5 min)
150
Figure 8.4 – Distribution components over time (Cross-section A).
Component
Distribution (%)
Density Current
Hor. Exchange
Tidal Filling
TOTAL
8%
51 %
42 %
100 %
Cell average &
time averaged
discharge (m3/s)
0.07
0.46
0.38
0.91
Ratio
Vertical:Horizontal
Circulation
0.16
Table 8-1 – Distribution and cell & time averaged discharge for the three components at section A.
86
Cross section B
Distribution Components over time (Cross Section B)
2.5
3
8.2.2
Density Currents
Horizontal Exchange
Tidal Filling
2
1.5
1
0.5
0
0
50
100
150
Component
Distribution (%)
Density Current
Hor. Exchange
Tidal Filling
TOTAL
10 %
50 %
40 %
100 %
Cell average &
time averaged
discharge (m3/s)
0.12
0.56
0.44
1.12
Ratio
Vertical:Horizontal
Circulation
0.21
Table 8-2 – Distribution and cell & time averaged discharge for the three components at section B.
87
Cross section C
Distribution Components over time (Cross Section C)
2.5
3
8.2.3
Density Currents
Horizontal Exchange
Tidal Filling
2
1.5
1
0.5
0
0
50
100
150
Figure 8.6 – Distribution components over time (Cross-section C).
Component
Distribution (%)
Density Current
Hor. Exchange
Tidal Filling
TOTAL
11 %
52 %
37 %
100 %
Cell average &
time averaged
discharge (m3/s)
0.12
0.58
0.42
1.12
Ratio
Vertical:Horizontal
Circulation
0.21
Table 8-3 – Distribution and cell & time averaged discharge for the three components at section C.
88
8.3 Analysis
The horizontal and vertical circulation were already determined in section 7.6.7. From the three
components, the density currents totally contributes to the vertical circulation, while the horizontal
exchange totally contributes to the horizontal circulation.
Figure 8.7 – Contribution of the three components to the horizontal and vertical circulation.
From all three cross sections we can see that there are two peaks and that the horizontal exchange
and tidal filling are dominant. The cause of the very low density currents is because of the fact that
the tip of the salt wedge is somewhere in front of the Botlek entrance (Hydro Meteo, 2004), however
in the model this tip is more seawards. Because of this the density gradient is smaller and thus the
currents due to density differences too. In fact it would be a good idea to use other sets of boundary
conditions that would approach the reality more.
There are two peaks, one between -4 hours with respect to High Water at Botlek and High Water at
Botlek. The other peak is located between +1 and +4 hours with respect to High Water at the mouth
of the Botlek. The first peak, which is higher is somewhere at -2½ hours w.r.t. HW Botlek, while the
other peak is at about +3 hours w.r.t. HW Botlek. It could be possible that there are some shifts
when modelling with other extreme boundary conditions (spring tide / high river discharge or neap
tide / low river discharge).
Further we can see that results cross sections B and C are quite similar. Cross section A shows a lower
value of the horizontal entrainment component, since this cross section is further away from the
theoretical mouth which is expected to be somewhere at B or C. Further in the report only the results
of cross section B will be represented.
89
9 EXCHANGE MECHANISMS AND
SEDIMENTATION
9.1 Sediment concentration measurements
For the transport of sediment we need the following two:
- Hydrodynamic flow (transport)
- Sediment itself (matter)
This can be red in the siltation rate formula described in section 3.6.2.4. Although the formula is
simplified it will still be used as we are more interested in the quality rather than quantity. The rate is
a multiplication of the trapping efficiency, exchange flow rate and ambient concentration. As was
said, the trapping efficiency is found to be nearly 100 % in the Botlek Harbour according M. de Nijs.
Until now there is one unknown: the sediment concentration in the Botlek Area. Old measurements
performed by De Nijs will be used as a basis. The advantage is that no new measurements have to be
made for this study. The focus of this study is more on the effects of the measurements rather than
knowing the exact siltation values. The disadvantage is that the site conditions were not the same
(mean tide & average discharge vs. spring tide & high discharge). This can never be the case since the
reality is more complex and the site conditions are not known beforehand when performing a
measurement. In the numerical model the conditions are specified, but we still deal with a model,
which is a representation of the reality. In addition we modelled an idealised situation where there is
an average tide and average discharge.
De Nijs used seven measuring stations, however not all measurements were shown in his report.
Station 3 and 4 were not shown, and therefore station 2 is taken as a reference since this one is the
nearest to the mouth of the Botlek Harbour.
th
Figure 9.1 – Measuring stations of the de Nijs’ survey on the 11 of April 2006 (De Nijs, 2010).
90
Figure 9.2 – The recorded water level, salinity and suspended particulate matter (top to bottom) at station 2 on the 11
of April 2006. Open circles are near bead measurements and dots are near surface measurements (De Nijs, 2010) .
th
In Figure 9.2 the recorded water level, salinity and suspended particulate matter are presented. The
suspended matter near bottom is higher than near surface as expected. There are clearly two peaks
when looking at the sediment concentration: one at ± 6.30 and one at ± 14.30 at high water. At other
hydrodynamical conditions some shifts can occur, however it is expected that these shift will not be
too large.
9.2 Combination of results
The idea is now to combine the results of the exchange mechanisms together with the sediment
measurements of 2006. This because both flow and sediment concentration are both important
when it comes to sedimentation.
Only one tide will be taken, since more tides will simply show repetitions of Figure 8.5 and Figure 9.2.
The results are presented in Figure 9.3 and according the flow and concentration data we have now,
the peaks do no coincide. This does not mean that we cannot apply measures. The expectation is
that the siltation rate will be the highest between -2 hours w.r.p HW Botlek and HW Botlek, and also
between +3 hours HW Botlek and +4 hours HW Botlek.
We want to investigate what kind of effects the measures will have on the exchange mechanisms,
and thus on the siltation rates (when combined with the concentration data). Again the focus is on
quality rather than quality. Further studies are needed to conclude whether a solution is costeffective or not. There are two goals (Figure 9.4 and Figure 9.5):
- The overall exchange flow should be as low as possible.
- The exchange flow should be low at times of high concentration. And the peaks should not
coincide at all.
91
Figure 9.3 – Combined results: exchange flows (cross section B) and sediment concentration (De Nijs, 2010).
92
Figure 9.4 – Goal 1: lowering of the exchange flows in general.
93
Figure 9.5 – Goal 2: Low flow rates at times of high concentrations.
94
95
10 MEASURES
10.1 Solutions to be investigated
The measures have to decrease the exchange flows between the river and the harbour. The density
currents are hard to lower, since they are mainly caused by salinity differences. We have already
seen in section 8.2 that in the selected situation these currents were low anyway. As for the tidal
filling we can take a look at the following formula:
QTide  Asurf 
dh
 u  Across
dt
(0.20)
According this formula the tidal exchange is a function of the harbour surface area and of the tide
itself. There is no way at all to change the natural tide, which leaves us only to one parameter that
can be changed artificially: the harbour surface area. A possible measure could be to make the
surface smaller by drying out a part of the Botlek Harbour that is not being used. As for all measures
we cannot say by forehand whether this is a good solution or not, because we always have to know
whether the benefits are higher than the loss.
There is one component which is very sensitive to the (harbour) geometry: the horizontal exchange
(see also section 3.6.2.1). The idea is to find measures that will lower the velocity differences
between the harbour and river, or with other words: to streamline the flow. A way to achieve that is
the use of a Current Deflecting Wall (with or without a sill) as described in section 3.6.3.3. However
there are some problems:
- The configuration of the CDW. The flow pattern can be changed drastically because of the
location of the CDW. Sometimes it can even make the problem worse. In addition high flows
can occur which are not good for navigational purposes.
- There is little space in the mouth of the Botlek for the CDW. The navigational width should
be guaranteed and not be too small.
- The CDW cannot be modelled properly in the used grid. A so called “stair-case” is formed
which can cause artificial roughness.
- In the used model sediment is not included and therefore the effect of a sill on
sedimentation cannot be seen.
Figure 10.1 – Mismatch cell boundaries and CDW.
96
Three variants are made as can be seen in section 10.2. Variant 2 is definitely not an option since the
navigational width is there too small. However this variant is still included to see what kind of effects
the configuration has on the flow pattern and exchange mechanisms. In addition two options are
made for this variant for further studies: with and without sill. The CDW’s of variant 1 and 3 is more
towards the westward dam and differs in the way it is bend to the harbour. Variant 3 is bend more
towards the harbour whereas the CDW at variant 1 is little bit more parallel to the river.
Another proposed solution is to make a gap in the east-dam in order to influence the flow dynamics.
The idea is to have some flow through the gap that counteracts on the flow through the mouth.
However the downside of this problem is:
- It is not known what kind of influence the gap has on the surface area of the harbour,
because the harbour is now open at two sides: the Botlek mouth and the gap. If it does have
an influence it will be translated by a high tidal filling component.
- The gap could create an extra sediment source for the Botlek Harbour. Further studies
(modelling with sediment and the use of scale models) can show whether this is the case.
Although the exchange flows could be lower, this measure can be rejected anyway by further
studies (e.g cost-benefit analysis).
- Just as with the Current Deflecting Wall, high flow velocities can occur which can have a
negative effect on shipping.
For this measure two variants are made as shown in section 10.3.
Compared to the other solutions the last measure is more easy to implement in practice: extending
the east-dam and making its tip more suitable for the flow. Again the goal is to streamline the water
flow and to minimise the exchange flows. Near the tip there is already an underwater dam as can be
seen in the dredging atlas in the Appendix on page 128. The idea is to fill this underwater dam until it
reaches the water surface, and therefore this solution is called filling underwater dam further in the
report.
Also this this solution suffers from modelling problems because of the resolution. The grid is actually
too coarse for making smooth boundaries. However from section 6.4.3 we have already seen that a
finer grid would result in very large computation times, so in this study a finer grid would not be a
practical choice.
Figure 10.2 – No smooth boundaries possible.
97
10.2 Current Deflecting Wall
10.2.1 Variant 1
10.2.2 Variant 2a
Figure 10.4 – CDW – Variant 2a.
98
10.2.3 Variant 2b
Figure 10.5 – CDW – Variant 2b.
10.2.4 Variant 3
99
10.3 Hole in Dam
10.3.1 Variant 1
10.3.2 Variant 2
100
10.4 Filling underwater dam
10.4.1 Variant 1
Figure 10.9 – Filling underwater dam – Variant 1.
101
11 RESULTS
11.1 No measures
The exchange mechanisms at cross section B (already given in 8.2.2) will be used as a reference when
compared to the results after the taken measures. The same colours will be used for the three
components:
- Black: density currents
- Red: horizontal exchange
- Blue: tidal filling
The distribution of the three components is 10%, 50% and 40% for the density current, horizontal
exchange and tidal filling respectively. After the taken measures we are more interested in the
change of magnitude of the three components individually, and all combined (total exchange). For
the magnitude the cell and time averaged discharge is used. By multiplying with the number of cells
in the cross section we obtain the total discharge. For the flow pattern, reference is made to the
Appendix.
Distribution Components over time (Cross Section B)
3
2.5
Density Currents
Horizontal Exchange
Tidal Filling
2
1.5
1
0.5
0
0
50
100
150
102
11.2 Current Deflecting Wall
11.2.1 Variant 1
Before
After
Distribution Components over time (Before)
Distribution Components over time (After)
2.5
2
1.5
1
0.5
0
2
3
3
2.5
0
50
100
1.5
1
0.5
0
150
0
50
100
150
Distribution
10 %
50 %
40 %
100 %
Before
(%)
Cell average &
time averaged
discharge (m3/s)
0.12
0.56
0.44
1.12
After
Component
Density Current
Hor. Exchange
Tidal Filling
TOTAL
Cell average &
time averaged
discharge (m3/s)
0.07
0.38
0.42
0.87
Growth/loss
percentage (%)
-42 %
-32 %
-5 %
-22 %
103
11.2.2 Variant 2a
Before
After
2.5
2
1.5
1
0.5
0
2
3
3
2.5
0
50
100
1.5
1
0.5
0
150
0
50
100
150
Figure 11.4 – CDW – Variant 2a. Exchange mechanisms before and after, cross section B.
Percentage
10 %
50 %
40 %
100 %
Before
Cell average &
time averaged
discharge (m3/s)
0.12
0.56
0.44
1.12
Component
Density Current
Hor. Exchange
Tidal Filling
TOTAL
After
Cell average &
Growth/loss
time averaged
percentage (%)
discharge (m3/s)
0.10
-17 %
1.42
+153 %
0.46
+5 %
1.98
+77 %
Table 11-2 – CDW – Variant 2a. Values before and after.
Figure 11.5 – CDW – Variant 2a. Lay-out.
104
11.2.3 Variant 2b
Before
After
2.5
2
1.5
1
0.5
0
2
3
3
2.5
0
50
100
1.5
1
0.5
0
150
0
50
100
150
Figure 11.6 – CDW – Variant 2b. Exchange mechanisms before and after, cross section B.
Percentage
10 %
50 %
40 %
100 %
Before
Cell average &
time averaged
discharge (m3/s)
0.12
0.56
0.44
1.12
Component
Density Current
Hor. Exchange
Tidal Filling
TOTAL
After
Cell average &
Growth/loss
time averaged
percentage (%)
discharge (m3/s)
0.12
0%
1.80
+221 %
0.47
+7 %
2.39
+113 %
Table 11-3 – CDW – Variant 2b. Values before and after.
Figure 11.7 – CDW – Variant 2b. Lay-out.
105
11.2.4 Variant 3
Before
After
2.5
2
1.5
1
0.5
0
2
3
3
2.5
0
50
100
1.5
1
0.5
0
150
0
50
100
150
Percentage
10 %
50 %
40 %
100 %
Before
Cell average &
time averaged
discharge (m3/s)
0.12
0.56
0.44
1.12
Component
Density Current
Hor. Exchange
Tidal Filling
TOTAL
After
Cell average &
Growth/loss
time averaged
percentage (%)
discharge (m3/s)
0.07
-42 %
0.46
-18 %
0.42
-5 %
0.95
-15 %
106
11.3 Hole in Dam
11.3.1 Variant 1
Before
After
2.5
2
1.5
1
0.5
0
2
3
3
2.5
0
50
100
1.5
1
0.5
0
150
0
50
100
150
Before
Percentage
Cell average &
time averaged
discharge (m3/s)
10 %
0.12
50 %
0.56
40 %
0.44
100 %
1.12
After
Component
Density Current
Hor. Exchange
Tidal Filling
TOTAL
Cell average &
time averaged
discharge (m3/s)
0.12
0.80
0.73
1.65
Growth/loss
percentage (%)
0%
+43 %
+66 %
+47 %
107
11.3.2 Variant 2
Before
After
2.5
2
1.5
1
0.5
0
2
3
3
2.5
0
50
100
1.5
1
0.5
0
150
0
50
100
150
Percentage
10 %
50 %
40 %
100 %
Before
Cell average &
time averaged
discharge (m3/s)
0.12
0.56
0.44
1.12
Component
Density Current
Hor. Exchange
Tidal Filling
TOTAL
After
Cell average &
Percentage
time averaged
discharge (m3/s)
0.12
0%
0.80
+43 %
0.72
+64 %
1.64
+46 %
108
11.4 Filling underwater dam
11.4.1 Variant 1
Before
After
2.5
2
1.5
1
0.5
0
2
3
3
2.5
0
50
100
1.5
1
0.5
150
0
0
50
100
150
Figure 11.14 – Filling underwater dam – Variant 1. Exchange mechanisms before and after, cross section B.
Percentage
10 %
50 %
40 %
100 %
Cell average &
time averaged
discharge (m 3/s)
0.12
0.56
0.44
1.12
Component
Density Current
Hor. Exchange
Tidal Filling
TOTAL
Cell average &
time averaged
discharge (m 3/s)
0.07
0.41
0.43
0.91
Growth/loss
percentage (%)
-42 %
-27 %
-3 %
-19 %
Table 11-7 – Filling underwater dam – Variant 1. Values before and after.
Figure 11.15 – Filling underwater dam – Variant 1. Lay-out.
109
11.5 Discussion
11.5.1 Density currents
No measures
CDW
Hole in dam
Filling dam
Variant
Value (m3/s)
1
2a
2b
3
1
2
1
0.12
0.07
0.10
0.12
0.07
0.12
0.12
0.07
Growth/loss
percentage (%)
-42 %
-17 %
0%
-42 %
0%
0%
-42 %
Table 11-8 – Effects of measures on density currents.
We have already seen that the density currents are very low compared to the other two
components. Because of this, these values are very sensitive in the models. With other words the
growth or loss percentages can be quite high according the table, but they do not have a real
meaning here since we already have very low values (10 % averaged over a tide).
11.5.2 Horizontal exchange
No measures
CDW
Hole in dam
Filling dam
Variant
Value (m3/s)
1
2a
2b
3
1
2
1
0.56
0.38
1.42
1.80
0.46
0.80
0.80
0.41
Growth/loss
percentage (%)
-32 %
+153 %
+ 221 %
-18%
+43 %
+43 %
-27 %
Table 11-9 – Effects of measures on the horizontal exchange.
Here we clearly can see that the flow is very sensitive to the configuration of the Current Deflecting
Wall. While variant 1 and 3 show a decrease in horizontal exchange, variant 2 shows an extraordinary
increase. This is both the case for the variant with a sill and the variant without a sill, where the one
without sill is worse.
110
11.5.3 Tidal filling
No measures
CDW
Hole in dam
Filling dam
Variant
Value (m3/s)
1
2a
2b
3
1
2
1
0.44
0.42
0.46
0.47
0.42
0.73
0.72
0.43
Growth/loss
percentage (%)
-5 %
+5 %
+7 %
-5%
+66 %
+64 %
-3 %
Table 11-10 – Effects of measures on tidal filling.
As was already described in section 10.1 the hole in the east-dam would have an effect on the
theoretical surface of the harbour. The magnitude could not be estimated a priori, but as we can see
in the table the increase of the tidal filling discharge is more than 60%. Because
dh
does not change,
dt
this means that the new surface area is increased by more than 60 % too when we look at the next
formula.
Q  Asurf 
dh
 u  Across
dt
(0.21)
The harbour area is kept the same for the other measures and can be seen in the results too. The
graphs showing the tidal components are very similar and there are only very small differences in
growth/loss percentages.
111
11.5.4 Total
No measures
CDW
Hole in dam
Filling dam
Variant
Value (m3/s)
1
2a
2b
3
1
2
1
1.12
0.87
0.46
2.39
0.95
1.98
1.65
0.91
Growth/loss
percentage (%)
-22 %
+77 %
+113 %
-15 %
+47 %
+46 %
-19 %
Table 11-11 – Effects of measures on total exchange flow.
When we look at the total exchange flow, we can see that only the 1 s t and 3rd variant of the Current
Deflecting Wall and the filling underwater dam solution are the only three variants that seem to have
good results. In those cases the decrease of the total exchange flow is 15-22%. Variant 2 is totally not
an option to decrease the sedimentation in the Botlek Harbour. The increase of 77% and 113% is
mainly because of the increase in horizontal exchange. The hole in the dam increases the total
exchange flow with almost 50%. This in because of the higher horizontal exchange and the higher
tidal filling both. The wanted result that was described in section 10.1 was thus not achieved.
We could say that the Current Deflecting Wall could be an option to decrease the exchange flow.
However the configuration should be chosen carefully as in can have either a positive effect of even a
very negative effect and thus make the problem even worse. The change from variant 1 to variant 2b
is a decrease of 237%.
The hole in the dam, does not seem to be a good option at all, whereas filling the dam surprisingly
gives already good results. CDW variant 1 and 3 and the filled dam are both qualified to make some
further studies on it.
112
113
12 CONCLUSION, DISCUSSION &
RECOMMENDATION
The sedimentation of the Botlek Harbour is a big problem as it goes together with very high dredging
costs for the Port of Rotterdam. Many solutions are presented in literature by experts all over the
world varying from hard measures that influence the hydrodynamics to soft measures. For example
the use of the CDW and tide depended dumping respectively. Since we deal with a very complex
problem, the problem had to be narrowed down for the sake of research quality.
First the idea was to analyse the dredge data and see whether there was a trend. However this trend
could not be found as the data set was too small. In addition, the dredge data does not necessarily be
system-driven as it could be capacity-driven as well. Perhaps the Port of Rotterdam could start a
study to make more use of the dredge data and ‘learn’ from it. In an ideal case the future
sedimentation could be predicted and resources could be allocated better, which directly has a
positive effect on costs.
Already in the past some measures were tried out to minimize the dredging costs. In this report two
measures were discussed: the silt trap and the silt screen. The silt trap seems to be positive as less
sediment goes further into the basis as seen in the figure showing the dredged cubic meter per
square meter a year. The dredge conditions are better and sediment is concentrated at on location.
In the study little information could be found about the silt trap. It would be a good idea to study the
silt traps more in depth.
There are many strategies to decrease the maintenance dredging costs. Each harbour is unique and
so is the Botlek Harbour. A strategy which worked at some ports does not necessarily have to work in
the harbours of Rotterdam. In this study the strategy was to keep the sediment out (KSO) by
decreasing the exchange flow mechanisms by the use of hard structures. Firstly, because the
problem had to be narrowed down anyway, secondly because there was no similar study on
exchange mechanisms for the Botlek Harbour and lastly, there would be resources to performed this
kind of study (e.g. the use of Delft3D). We have to keep in mind that are many strategies to decrease
the costs.
Numerical models were used to gain more insight in the hydrodynamics, but also to examine some
proposed solutions. The trade-off between required resolution and time was very hard to find. Later
on in the study it turned out that the grid was still not good enough as the were some problems
modelling the proposed measures. The problem was that the CDW for example could not be
modelled nicely on the cell boundaries with as a result a stair-case boundary. For a qualitative
analysis of the exchange mechanisms this was not really a problem. However if a detailed study is to
be made, the resolution must be finer and in addition the grid can be made such that measures are
easier to model.
114
Continuing with numerical models, another improvement is to include sediment in the model. The
focus was more on the exchange flow and therefore sediment was kept away in the model as it
would make the models too time consuming because of the extra equations. Anyhow, no hard
conclusions can be drawn without a proper model including sediment. For further studies the
sediment must be included in the models too.
As for the boundary conditions also something can be said about it. In the models only one set of
boundary conditions was used: an average tide & an average river discharge. Later on it turned out
that the salt wedge did not reach Botlek but was more seawards, while it is known that it does reach
the mouth in reality. To control whether this is a because of the chosen boundaries or because of the
model itself, other sets must be used as well. In this case a lower discharge would make the wedge
go more towards the Botlek. If this is not the case, or the wedge is not moving far enough there
could be a problem within the model itself. Also because of this no hard conclusions can be made for
the proposed solutions as only one set of boundary conditions is modelled.
However the results gives good first order results that can be used for future detailed studies. Some
conclusion can be drawn. First of all it could be seen that the flow mechanisms are very sensitive to
the configuration of the Current Deflecting Wall. While for the best variant there was a loss of 22%,
for the worse variant the exchange flow increased by 113%. Little change in location made sure that
the total exchange flow increased with 237%. The model indeed showed that the Current Deflecting
Wall is very likely to reduce sedimentation as it reduced exchange flows too.
The hole in the dam is definitely not an option as the exchange flow increases by almost 50%.
Furthermore this solution was anyway hard to implement in practice, but was still included to see if
there was any change and to what extent. Although solutions seem to be hard to implement in
reality, there is always one question that is important: is the gain higher than the loss. And also for
the sake of insight, solutions which seemed to be not practical (e.g. the Current Deflecting Wall
variant 2 which caused a too small navigation width) were modelled anyway.
We can also conclude that geometries of harbour mouths are very important for streamlining the
flow, which on turn results in lower exchange flows. Even with a rough grid inducing a stair-case
boundary the model showed that filling the underwater dam resulted in an exchange flow decrease
of 19%.
115
The results are not a hard proof that certain measures are the right solution, since further study is
needed for that. However is was shown that certain measures influence the exchange mechanisms
and it is known that these mechanisms are very important in the study of sedimentation. It is very
likely that some CDW configurations and the filling of the underwater dam would have a positive
effect when it comes to sedimentation.
However, some steps must be performed to draw ‘hard’ conclusions (Figure 12.1). Firstly many
things have to be done to improve the models, for example by using a higher spatial resolution
and/or another type of grid. Secondly, other sets of conditions must be modelled as well to see
whether the reality can be better approached and what kind of effect this has on exchange flows. In
addition, sediment must be included in the models to have more insight on the sedimentation itself
and the long term effects of it. After that a feasibility study must be made, including a cost-benefit
analysis. It would be wise to improve the models further and to make a scale model for the most
feasible solution. In the ideal case, were all results are positive and hard conclusion can be made, it
would be a good idea for the Port of Rotterdam to start a pilot. This because reducing maintenance
dredging costs is in line with the goal of the Port of Rotterdam to be the most competitive,
innovative and sustainable port in the world.
Figure 12.1 – Steps to be taken.
116
117
13 LITERATURE
Bosboom, J. Stive, M. (2010)
Coastal Dynamics 1.
Tu Delft.
Deltares (2011)
Delft3D-FLOW User Manual.
Deltares (2007)
Validation Document Delft3D-FLOW
De Nijs, M. Winterwerp, J. Pietrzak, J. (2008)
On harbour siltation in the fresh water mixing region.
Science Direct
De Nijs, M. Winterwerp, J. Pietrzak, J. (2010)
The effects of the internal flow structure on SPM entrapment in the Rotterdam Waterway.
Journal of Physical Oceanography
Dyer, K. (2001)
Estuarine Circulation
Eysink, W.D. (1989)
Sedimentation in harbour basins. Small density differences may cause serious effects.
Hulsen, L. (2011)
Type: “internal communication”
Port of Rotterdam
Kessel, T. (1997)
Generation and transport of subaqueous fluid mud layers.
PhD Thesis TU Delft
Nielsen, P. (2009)
Coastal and Estuarine Processes.
World Scientific.
PIANC (2006)
Minimising harbour siltation: recommendations of PIANC working group 43.
Port of Rotterdam (2004)
Hydro Meteo informatiebundel nr. 3.
118
Port of Rotterdam (2011)
Hydro Meteo informatiebundel nr. 4 (concept).
Pye, K. (1994)
Sediment transport and depositional processes.
Blackwell Scientific Publications.
Rijkswaterstaat (2011).
Getijtafels voor Nederland 2012.
Rijkswaterstaat (2004).
Huidige situatie en autonome ontwikkeling Rijk-Maasmonding.
Rijkswaterstaat (2007)
Reductie sedimentatie in havens. Onderzoek naar kansrijke oplossingen.
Rijkswaterstaat (2003)
Voorkomen van sedimentatie in havens. Verkenning van maatregelen. Rijkswaterstaat DWW.
Rotterdam & Rijkswaterstaat (1987)
Minimalisering Kosten Onderhoudsbaggerwerk
Winterwerp, J. Kuijper, C. (2003)
The Current Deflecting Wall: mitigating harbour siltation
Deltares
Winterwerp, J. (2010)
On the modelling of fluid mud (presentation)
Deltares
www.mx-systems.nl/osr
OSR measurements and predictions.
Port of Rotterdam
119
Sedimentation in the Botlek Harbour A research into driving water exchange mechanisms.
Master Thesis
APPENDIX
Adil El Hamdi
120
Jan 2011
121
APPENDIX A – MAP PORT OF ROTTERDAM
122
123
124
125
126
127
APPENDIX B – DREDGE ATLAS BOTLEK
Figure 0.1 – Dredge atlas.
128
129
APPENDIX C – DREDGE DATA 1995-2010,
BOTLEK AREA
130
131
APPENDIX D – ASSUMPTIONS AND
APPROXIMATIONS D3D
Figure 0.1 – Assumptions and approximations D3D (Validation Document Delft3D-Flow, 2007.
132
133
APPENDIX E – CROSS SECTIONS MOUTH BOTLEK
E.1 – Cross section A
Figure 0.1 – Cross section A (looking from South to North).
E.2 – Cross section B
Figure 0.2 – Cross section B (looking from South to North).
134
E.3 – Cross section C
Figure 0.3 – Cross section C (looking from South to North).
135
APPENDIX F – USED DEPTHS FOR SCRIPT
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
A
11.44
12.94
14.22
14.89
15.23
15.31
15.27
15.23
14.83
13.73
12.36
10.46
9.10
8.20
7.87
7.86
7.93
8.03
8.27
8.66
9.00
9.11
8.94
9.27
9.69
B
10.83
12.57
14.36
15.36
15.71
15.76
15.30
14.20
12.87
11.68
10.71
10.00
9.20
8.07
7.26
7.25
6.50
C
8.51
9.83
11.56
13.96
15.34
15.31
15.19
15.04
15.11
15.12
14.96
14.76
14.29
13.44
12.41
10.92
8.97
Table 0-1 – Used depths for script (meter).
136
137
APPENDIX G – TRANSFORMATION Σ TO Z-PLANE
Figure 0.1 – From σ-plane to z-plane.
138
139
APPENDIX H – PART OF MATLAB SCRIPT
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%
%%%%%%%%%%%
%%%%%%%%%%%
CALCULATION HORIZONTAL AND VERTICAL CIRCULATION
%%%%%%%%%%%
%%%%%%%%%%%
IN A HARBOUR/RIVER CROSS SECTION
%%%%%%%%%%%
%%%%%%%%%%%
%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
clear all;
clc;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%% INPUT %%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Sim =
cs =
layers =
obspoints =
6;
'B';
20;
17;
%
%
%
%
Simulation number
Cross-section
Number of layers
Number of observation points
d1 =
10.83;
variables = number of observation points) [m]
d2 =
12.57;
d3 =
14.36;
d4 =
15.36;
d5 =
15.71;
d6 =
15.76;
d7 =
15.30;
d8 =
14.20;
d9 =
12.87;
d10 =
11.68;
d11 =
10.71;
d12 =
10.00;
d13 =
9.20;
d14 =
8.07;
d15 =
7.26;
d16 =
7.25;
d17 =
6.50;
zmax =
zstep =
16;
0.1;
w1 =
470;
of z-points needed at output) [m]
w2 =
470;
w3 =
470;
w4 =
470;
w5 =
468;
w6 =
463;
w7 =
457;
w8 =
405;
w9 =
376;
w10 =
349;
w11 =
316;
w12 =
262;
w13 =
222;
w14 =
171;
w15 =
142;
w16 =
0;
wsurface =
470;
% Depth at observation points (Note: amount of
% Desired vertical length for output [m]
% Desired vertical steps for output [m]
% Width at depths (Note: amount of variables = number
% Width at surface [m]
addpath(['C:/Users/X/Desktop/Simulations/Sim ' num2str(Sim) '/Output/']);
140
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%% SCRIPT %%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Import data (Note: number of variables = number of observation points) %
b1 = importdata(['hv_' cs '1.csv']);
B1 = b1.data;
B2 = b2.data;
B3 = b3.data;
B4 = b4.data;
B5 = b5.data;
B6 = b6.data;
B7 = b7.data;
B8 = b8.data;
B9 = b9.data;
B10 = b10.data;
B11 = b11.data;
B12 = b12.data;
B13 = b13.data;
B14 = b14.data;
B15 = b15.data;
B16 = b16.data;
B17 = b17.data;
timesteps = length(B1(:,1));
% Number of time steps
% Calculation of mean cross sectional velocity %
for n=1:timesteps;
q(n,1) = sum(B1(n,:)) + sum(B2(n,:)) + sum(B3(n,:)) + sum(B4(n,:)) + sum(B5(n,:)) +
sum(B6(n,:)) + sum(B7(n,:)) + sum(B8(n,:)) + sum(B9(n,:)) + sum(B10(n,:)) + sum(B11(n,:)) +
sum(B12(n,:)) + sum(B13(n,:)) + sum(B14(n,:)) + sum(B15(n,:)) + sum(B16(n,:)) + sum(B17(n,:));
C(n,1) = q(n,1) / (layers * obspoints);
time
end
% Mean cross sectional velocity as a function of
% Interpolation (number of sets = number of observation points)%
xi = [0:zstep:zmax];
yi = [1:timesteps]';
% Interpolation points z-direction
% Interpolation points t-direction
%%% Obs 1
%
The
corresponding
coordinates Delft
3D
output
[m]
for j=1:layers
x1(j)=(j-0.5)/layers*d1;
end
y1 = [1:timesteps]';
141
K1 = interp2(x1,y1,B1,xi,yi);
interpolation
K1(isnan(K1))= 0;
by zero
s1 = 0.5*d1/layers/zstep+1;
layer values
for r = 1:s1
K1(:,r)=B1(:,1);
end
% Transformation from sigma-plane to z-plane by
% Replacing vales above (top) and below (bottom)
% Replacing the top zero values by the top sigma-
%%% Obs 2
for j=1:layers
end
K2(isnan(K2))= 0;
for r = 1:s2
K2(:,r)=B2(:,1);
end
%%% Obs 3
for j=1:layers
end
K3(isnan(K3))= 0;
for r = 1:s3
K3(:,r)=B3(:,1);
end
%%% Obs 4
for j=1:layers
end
K4(isnan(K4))= 0;
for r = 1:s4
K4(:,r)=B4(:,1);
end
%%% Obs 5
for j=1:layers
end
K5(isnan(K5))= 0;
for r = 1:s5
K5(:,r)=B5(:,1);
end
%%% Obs 6
for j=1:layers
end
142
K6(isnan(K6))= 0;
for r = 1:s6
K6(:,r)=B6(:,1);
end
%%% Obs 7
for j=1:layers
end
K7(isnan(K7))= 0;
for r = 1:s7
K7(:,r)=B7(:,1);
end
%%% Obs 8
for j=1:layers
end
K8(isnan(K8))= 0;
for r = 1:s8
K8(:,r)=B8(:,1);
end
%%% Obs 9
for j=1:layers
end
K9(isnan(K9))= 0;
for r = 1:s9
K9(:,r)=B9(:,1);
end
%%% Obs 10
for j=1:layers
x10(j)=(j-0.5)/layers*d10;
end
K10(isnan(K10))= 0;
for r = 1:s10
K10(:,r)=B10(:,1);
end
%%% Obs 11
for j=1:layers
x11(j)=(j-0.5)/layers*d11;
end
K11(isnan(K11))= 0;
143
for r = 1:s11
K11(:,r)=B11(:,1);
end
%%% Obs 12
for j=1:layers
x12(j)=(j-0.5)/layers*d12;
end
K12(isnan(K12))= 0;
for r = 1:s12
K12(:,r)=B12(:,1);
end
%%% Obs 13
for j=1:layers
x13(j)=(j-0.5)/layers*d13;
end
K13(isnan(K13))= 0;
for r = 1:s13
K13(:,r)=B13(:,1);
end
%%% Obs 14
for j=1:layers
x14(j)=(j-0.5)/layers*d14;
end
K14(isnan(K14))= 0;
s14 = 0.5*d14/layers/zstep;
for r = 1:s14
K14(:,r)=B14(:,1);
end
%%% Obs 15
for j=1:layers
x15(j)=(j-0.5)/layers*d15;
end
K15(isnan(K15))= 0;
for r = 1:s15
K15(:,r)=B15(:,1);
end
%%% Obs 16
for j=1:layers
x16(j)=(j-0.5)/layers*d16;
end
K16(isnan(K16))= 0;
for r = 1:s16
K16(:,r)=B16(:,1);
144
end
%%% Obs 17
for j=1:layers
x17(j)=(j-0.5)/layers*d17;
end
K17(isnan(K17))= 0;
for r = 1:s17
K17(:,r)=B17(:,1);
end
%%%
% CIRCULATION %
for n = 1:timesteps;
% horiontal circulation as a function of y (Note: number of sets is number of
points) [m/s] %
D(n,1)
D(n,2)
D(n,3)
D(n,4)
D(n,5)
D(n,6)
D(n,7)
D(n,8)
D(n,9)
D(n,10)
D(n,11)
D(n,12)
D(n,13)
D(n,14)
D(n,15)
D(n,16)
D(n,17)
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
abs(
abs(
abs(
abs(
abs(
abs(
abs(
abs(
abs(
abs(
abs(
abs(
abs(
abs(
abs(
abs(
abs(
C(n,1)C(n,1)C(n,1)C(n,1)C(n,1)C(n,1)C(n,1)C(n,1)C(n,1)C(n,1)C(n,1)C(n,1)C(n,1)C(n,1)C(n,1)C(n,1)C(n,1)-
observation
sum(K1(n,:)) /d1*zstep );
sum(K10(n,:))/d10*zstep);
% vertical circulation as a function of z (Note: number of sets is number of desired layers of
z plane) [m/s] %
E(n,1) = abs( C(n,1) - sum( K1(n,5)
+ K2(n,5)
K6(n,5)
+ K7(n,5)
+ K8(n,5)
+ K9(n,5)
+
K13(n,5)
+ K14(n,5)
+ K15(n,5)
round(w1/wsurface*obspoints) );
E(n,2) = abs( C(n,1) - sum( K1(n,15)
+ K2(n,15)
K6(n,15)
+ K7(n,15)
+ K8(n,15)
+ K9(n,15)
+
K13(n,15)
+ K14(n,15)
+ K15(n,15)
E(n,3) = abs( C(n,1) - sum( K1(n,25)
+ K2(n,25)
K6(n,25)
+ K7(n,25)
+ K8(n,25)
+ K9(n,25)
+
K13(n,25)
+ K14(n,25)
+ K15(n,25)
E(n,4) = abs( C(n,1) - sum( K1(n,35)
+ K2(n,35)
K6(n,35)
+ K7(n,35)
+ K8(n,35)
+ K9(n,35)
+
K13(n,35)
+ K14(n,35)
+ K15(n,35)
E(n,5) = abs( C(n,1) - sum( K1(n,45)
+ K2(n,45)
K6(n,45)
+ K7(n,45)
+ K8(n,45)
+ K9(n,45)
+
K13(n,45)
+ K14(n,45)
+ K15(n,45)
E(n,6) = abs( C(n,1) - sum( K1(n,55)
+ K2(n,55)
K6(n,55)
+ K7(n,55)
+ K8(n,55)
+ K9(n,55)
+
K13(n,55)
+ K14(n,55)
+ K15(n,55)
+ K3(n,5)
+ K4(n,5)
+ K5(n,5)
K10(n,5)
+ K11(n,5)
+ K12(n,5)
+ K16(n,5)
+ K17(n,5)
)
+
+
/
+ K3(n,15)
+ K4(n,15)
+ K5(n,15)
K10(n,15)
+ K11(n,15)
+ K12(n,15)
+ K16(n,15)
+ K17(n,15)
)
+
+
/
+ K3(n,25)
+ K4(n,25)
+ K5(n,25)
K10(n,25)
+ K11(n,25)
+ K12(n,25)
+ K16(n,25)
+ K17(n,25)
)
+
+
/
+ K3(n,35)
+ K4(n,35)
+ K5(n,35)
K10(n,35)
+ K11(n,35)
+ K12(n,35)
+ K16(n,35)
+ K17(n,35)
)
+
+
/
+ K3(n,45)
+ K4(n,45)
+ K5(n,45)
K10(n,45)
+ K11(n,45)
+ K12(n,45)
+ K16(n,45)
+ K17(n,45)
)
+
+
/
+ K3(n,55)
+ K4(n,55)
+ K5(n,55)
K10(n,55)
+ K11(n,55)
+ K12(n,55)
+ K16(n,55)
+ K17(n,55)
)
+
+
/
145
E(n,7) = abs( C(n,1) - sum( K1(n,65)
+ K2(n,65)
K6(n,65)
+ K7(n,65)
+ K8(n,65)
+ K9(n,65)
+
K13(n,65)
+ K14(n,65)
+ K15(n,65)
E(n,8) = abs( C(n,1) - sum( K1(n,75)
+ K2(n,75)
K6(n,75)
+ K7(n,75)
+ K8(n,75)
+ K9(n,75)
+
K13(n,75)
+ K14(n,75)
+ K15(n,75)
E(n,9) = abs( C(n,1) - sum( K1(n,85)
+ K2(n,85)
K6(n,85)
+ K7(n,85)
+ K8(n,85)
+ K9(n,85)
+
K13(n,85)
+ K14(n,85)
+ K15(n,85)
E(n,10) = abs( C(n,1) - sum( K1(n,95)
+ K2(n,95)
K6(n,95)
+ K7(n,95)
+ K8(n,95)
+ K9(n,95)
+
K13(n,95)
+ K14(n,95)
+ K15(n,95)
E(n,11) = abs( C(n,1) - sum( K1(n,105) + K2(n,105)
K6(n,105) + K7(n,105) + K8(n,105) + K9(n,105) +
K13(n,105)
+
K14(n,105)
+
K15(n,105)
E(n,12) = abs( C(n,1) - sum( K1(n,115) + K2(n,115)
K6(n,115) + K7(n,115) + K8(n,115) + K9(n,115) +
K13(n,115)
+
K14(n,115)
+
K15(n,115)
E(n,13) = abs( C(n,1) - sum( K1(n,125) + K2(n,125)
K6(n,125) + K7(n,125) + K8(n,125) + K9(n,125) +
K13(n,125)
+
K14(n,125)
+
K15(n,125)
E(n,14) = abs( C(n,1) - sum( K1(n,135) + K2(n,135)
K6(n,135) + K7(n,135) + K8(n,135) + K9(n,135) +
K13(n,135)
+
K14(n,135)
+
K15(n,135)
E(n,15) = abs( C(n,1) - sum( K1(n,145) + K2(n,145)
K6(n,145) + K7(n,145) + K8(n,145) + K9(n,145) +
K13(n,145)
+
K14(n,145)
+
K15(n,145)
E(n,16) = 0;
end
+ K3(n,65)
+ K4(n,65)
+ K5(n,65)
K10(n,65)
+ K11(n,65)
+ K12(n,65)
+ K16(n,65)
+ K17(n,65)
)
+
+
/
+ K3(n,75)
+ K4(n,75)
+ K5(n,75)
K10(n,75)
+ K11(n,75)
+ K12(n,75)
+ K16(n,75)
+ K17(n,75)
)
+
+
/
+ K3(n,85)
+ K4(n,85)
+ K5(n,85)
K10(n,85)
+ K11(n,85)
+ K12(n,85)
+ K16(n,85)
+ K17(n,85)
)
+
+
/
+ K3(n,95)
+ K4(n,95)
+ K5(n,95)
K10(n,95)
+ K11(n,95)
+ K12(n,95)
+ K16(n,95)
+ K17(n,95)
)
+
+
/
+ K3(n,105) + K4(n,105) + K5(n,105)
K10(n,105) + K11(n,105) + K12(n,105)
+
K16(n,105)
+
K17(n,105)
)
+
+
/
+ K3(n,115) + K4(n,115) + K5(n,115)
K10(n,115) + K11(n,115) + K12(n,115)
+
K16(n,115)
+
K17(n,115)
)
+
+
/
+ K3(n,125) + K4(n,125) + K5(n,125)
K10(n,125) + K11(n,125) + K12(n,125)
+
K16(n,125)
+
K17(n,125)
)
+
+
/
+ K3(n,135) + K4(n,135) + K5(n,135)
K10(n,135) + K11(n,135) + K12(n,135)
+
K16(n,135)
+
K17(n,135)
)
+
+
/
+ K3(n,145) + K4(n,145) + K5(n,145)
K10(n,145) + K11(n,145) + K12(n,145)
+
K16(n,145)
+
K17(n,145)
)
+
+
/
display('Finished')
%%% Horizontal and vertical circulation - Tidally averaged %%%
% Input %
va = 0.31;
% Vertical axis max
% Average horizontal circulation over time %
for e = 1:obspoints
Davg(1,e) = e - 0.5;
end
Davg(2,:) = mean(D);
subplot(2,1,1)
% Plot
plot(Davg(1,:),Davg(2,:));
title(['Horizontal circulation averaged over tide in cross section ' cs])
xlabel('y')
ylabel('horizontal circulation (m/s)')
axis([0 obspoints 0 va])
146
% Average vertical circulation over period %
for f = 1:zmax
Eavg(1,f) = f - 0.5;
end
Eavg(2,:) = mean(E);
subplot(2,1,2)
% Plot
plot(Eavg(1,:)*-1,Eavg(2,:));
% Note: vertical coordinates are negative here
title(['Vertical circulation averaged over tide in cross section ' cs])
xlabel('z')
ylabel('vertical circulation (m/s)')
axis([-16 0 0 va])
saveas(gcf,['Cross section ' cs ' - Tidally averaged circulation.png'])
% Export file to PNG
%%% Ratio horizontal and vertical circulation %%%
clc
% Cross sectional average horizontal circulation over period %
DD = mean(mean(D));
display(['Horizontal circulation
num2str(DD), ' m/s'])
-
tidally
averaged
-
cross
sectional
averaged
=
',
=
',
% Cross sectional average vertical circulation over period %
EE = mean(mean(E));
display(['Vertical
num2str(EE), ' m/s'])
circulation
-
tidally
averaged
-
cross
sectional
averaged
% Ratio horizontal/total %
display(['Ratio horizontal/total circulation =
', num2str(round(DD/(DD+EE)*100)), ' %'])
% Ratio horizontal/total %
display(['Ratio verical/total
circulation =
', num2str(round(EE/(DD+EE)*100)), ' %'])
147
APPENDIX I – OBSERVATION POINTS.
148
149
APPENDIX J – VALIDATION FLOW VELOCITIES
HW -6
150
HW -4
151
HW -2
152
HW at Hoek van Holland
153
HW +2
154
HW +4
155
HW +6
156
157
APPENDIX K – DEPTH AVERAGED VELOCITY PROFILE - CDW – VARIANT 1
158
Before
-6 H HW Botlek
After
Before
-4 H HW Botlek
After
159
Before
-2 H HW Botlek
After
Before
HW Botlek
After
160
Before
+2 H HW Botlek
After
Before
+4 H HW Botlek
After
161
APPENDIX L – DEPTH AVERAGED VELOCITY PROFILE - CDW – VARIANT 2A
162
Before
-6 H HW Botlek
After
Before
-4 H HW Botlek
After
163
Before
-2 H HW Botlek
After
Before
HW Botlek
After
164
Before
+2 H HW Botlek
After
Before
+4 H HW Botlek
After
165
APPENDIX M – DEPTH AVERAGED VELOCITY PROFILE - CDW – VARIANT 2B
166
Before
-6 H HW Botlek
After
Before
-4 H HW Botlek
After
167
Before
-2 H HW Botlek
After
Before
HW Botlek
After
168
Before
+2 H HW Botlek
After
Before
+4 H HW Botlek
After
169
APPENDIX N – DEPTH AVERAGED VELOCITY PROFILE - CDW – VARIANT 3
170
Before
-6 H HW Botlek
After
Before
-2 H HW Botlek
After
171
Before
+2 H HW Botlek
After
Before
+4 H HW Botlek
After
172
173
APPENDIX O – DEPTH AVERAGED VELOCITY PROFILE - HOLE IN DAM – VARIANT 1
174
Before
-6 H HW Botlek
After
Before
-2 H HW Botlek
After
175
Before
HW Botlek
After
Before
+2 H HW Botlek
After
176
Before
+4 H HW Botlek
After
Before
+6 H HW Botlek
After
177
APPENDIX P – DEPTH AVERAGED VELOCITY PROFILE - HOLE IN DAM – VARIANT 2
178
Before
-6 H HW Botlek
After
Before
-2 H HW Botlek
After
179
Before
HW Botlek
After
Before
+2 H HW Botlek
After
180
Before
+4 H HW Botlek
After
Before
+6 H HW Botlek
After
181
APPENDIX Q – DEPTH AVERAGED VELOCITY PROFILE - FILLING UNDERWATER
DAM – VARIANT 1
182
Before
-6 H HW Botlek
After
Before
-2 H HW Botlek
After
183
Before
+1 H HW Botlek
After
Before
+3 H HW Botlek
After
184
185
APPENDIX R – HORIZONTAL FLOW PATTERN AROUND BOTLEK MOUTH
186
HW -6h
Top
Middle
Bottom
HW -4h
Top
Middle
Bottom
HW -2h
187
Top
Middle
Bottom
HW Hoek van Holland
Top
Middle
Bottom
188
HW Hoek van Holland
Top
Middle
Bottom
HW +2h
Top
Middle
Bottom
189
HW +4h
Top
Middle
Bottom
HW +6h
Top
Middle
Bottom
190
191
APPENDIX S – TOTAL FLOW THROUGH CROSS SECTIONS
192
HW -6h
A
B
C
HW -4h
A
B
C
193
HW -2h
A
B
C
HW Hoek van Holland
A
B
C
194
HW Hoek van Holland
A
B
C
HW +2h
A
B
C
195
HW +4h
A
B
C
HW +6h
A
B
C
196
197
APPENDIX T – DECOMPOSED FLOW THROUGH CROSS SECTIONS
RED: Inflow
BLUE: Outflow
198
Density Current
Horizontal Exchange
Tidal Filling
199
Density Current
Horizontal Exchange
Tidal Filling
200
HW Botlek
Density Current
Horizontal Exchange
Tidal Filling
201
Density Current
Horizontal Exchange
Tidal Filling
202
Density Current
Horizontal Exchange
Tidal Filling
203
204

Sedimentation in the Botlek Harbour

Transcription

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