dsd-nl 2014 - nghs flexible mesh - optimizing harbour maintenance strategies using delft3d flexible...

Optimizing harbour maintenance

strategies using Delft3D - Flexible

Mesh

20 juni 2014

Robert Hasselaar, Arjen Luijendijk, Wiebe de Boer

- 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)

- 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

Harlingen harbour located in barrier island system in

the north of Holland

- 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

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

Horizontal Eddy circulation

Three distinct processes contribute to the harbour

siltation (II/III)

Density driven vertical circulation

Three distinct processes contribute to the harbour

siltation (III/III)

fresh salt

Sluice Sea

- 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)

Experienced difficulties during numerical study using

Delft3D software package (II/II)

- 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)

- 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)

D-Flow Flexible Mesh promising candidate to solve

the problems encoutered (III/III)

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

ModelNumber of grid cells

Both models perform equally well in prediction of

water levels

White = D3D curv

Red = FM 1

Yellow = FM 2

Model outcomes show small differences in velocity

comparison

More pronounced stratification in Delft3D Flexible

Mesh models

More pronounced stratification in Delft3D Flexible

Mesh models

- 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

Tidal filling and emptying largest share in gross water

exchange

Flood

Ebb

~30%

~20%

~50%

density (kg/m3)

concentration (g/l)

Tide and density current main contributors to

sedimentation

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

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