This document discusses using Delft3D Flexible Mesh (FM) to optimize harbour maintenance strategies by gaining insights into sedimentation processes. FM allows for more efficient modeling of complex harbour geometries. Three models were set up to evaluate FM performance: a curvilinear grid model and two FM models. Both FM models performed equally well in predicting water levels and showed small differences in velocity compared to the curvilinear model. FM also showed more pronounced stratification. Tidal filling and emptying was found to be the largest contributor to water exchange, while tide and density currents were the main contributors to sedimentation. FM is identified as a promising tool for siltation studies as it allows high resolution where needed and integration of 1D

1. Optimizing harbour maintenance
strategies using Delft3D - Flexible
Mesh
20 juni 2014
Robert Hasselaar, Arjen Luijendijk, Wiebe de Boer

2. - Sedimentation of fine sediments
- Requires frequent and expensive maintenance dredging
Many harbours around the world experience a large
annual siltation volume
Source: Harbour siltation (van Rijn 2012)
Country Harbour Siltation volume
Irak Um Qasr 1300000 (m3/y)
India New Mangalore Port 900000 (m3/y)
USA Mayport Naval Basin 380000 (m3/y)

3. - Goal numerical modelling
- Gain insights in processes responsible for siltation
- Problems with numerical modelling
- Complex geometries of harbours
- High resolution in areas of lesser importance
- Nesting required in larger scale numerical models
Numerical modelling used to investigate siltation
problems in harbours

4. Harlingen harbour located in barrier island system in
the north of Holland

5. - Tidal filling and emptying
- Horizontal eddy circulation
- Density driven vertical circulation
 Identify appropriate, effective mitigating measures against siltation
Project started to investigate relative importance of
sedimentation processes in Harlingen harbour

6. Tidal filling and emptying
Three distinct processes contribute to the harbour
siltation (I/III)
- Stirring by wind and waves
- Fines in suspension
- Low currents
- Settling of fines
Waddensea harbour
Ebb: export
Flood: import
Nett effect: import > export  siltation

7. Horizontal Eddy circulation
Three distinct processes contribute to the harbour
siltation (II/III)

8. Density driven vertical circulation
Three distinct processes contribute to the harbour
siltation (III/III)
freshsalt
SluiceSea

9. - Complex harbour geometry (curvilinear grid)
- High resolution throughout entire computational grid
- Nesting required in larger Waddensea model
Experienced difficulties during numerical study using
Delft3D software package (I/II)

10. Experienced difficulties during numerical study using
Delft3D software package (II/II)

11. - Flexible Mesh  structured and unstructured grids
- Allows for more efficient model setup
- Freedom in application high resolution grid cells
- Allows for more flexible model setup
- Good alignment with complex geometries
D-Flow Flexible Mesh promising candidate to solve
the problems encoutered (I/III)

12. - Automatic time step calculation
𝑣∆𝑡
∆𝑥
= 𝐶
- Combination Curvilinear & Flexible Mesh grids
- Calculate per time step & online adjustments
- X-Y specified BC / obs / crs
- NetCDF output
- Multicore standard
D-Flow Flexible Mesh promising candidate to solve
the problems encoutered (II/II)

13. D-Flow Flexible Mesh promising candidate to solve
the problems encoutered (III/III)

14. Three model applications setup to evaluate FM
performance and accuracy
Inside harbour Outside harbour Total
D3D curvilinear 2722 25364 28086
FM model 1 2722 25364 28086
FM model 2 8027 8570 16597
Model
Number of grid cells

15. Both models perform equally well in prediction of
water levels

16. White = D3D curv
Red = FM 1
Yellow = FM 2
Model outcomes show small differences in velocity
comparison

17. More pronounced stratification in Delft3D Flexible
Mesh models

18. More pronounced stratification in Delft3D Flexible
Mesh models

19. - Tidal filling and emptying
- Horizontal eddy circulation
- Density driven vertical circulation
Contributions to water motion in harbour opening
differ for each sedimentation process (I/II)
Net discharge ≠ 0 Net discharge = 0 Net discharge = 0

20. Tidal filling and emptying largest share in gross water
exchange
Flood
Ebb
~30%
~20%
~50%

21. density (kg/m3)
concentration (g/l)
Tide and density current main contributors to
sedimentation

22. I: insight in relative importance of siltation processes
- Tide and density driven currents main contributors
- Identify appropriate, effective mitigating measures
II: The Flexible Mesh allows for more efficient and flexible modelling
- Resolution in areas of interest
- Good alignment with complex geometries
Flexible Mesh approach combined with analysis water
motion seems promising tool for siltation studies

23. 2D model of open sea
3D model of Harlingen harbour
1D model of hinterland riverine system
Questions?
D-Flow Flexible Mesh will allow for a integrated 1D-
2D-3D modelling approach