intro story Coast / Estuary

Coast / Estuary

Coastal systems are among the most dynamic physical systems on earth and are subject to a large variety of forces. The morphodynamic changes occurring to coastlines worldwide are of great interest and importance. These changes occur as a result of the erosion of sediments, its subsequent transport as bed load or suspended load, and eventual deposition. 
 
Estuaries are partly enclosed water bodies that have an open connection to the coast. Estuaries generally have one or more branching channels, intertidal mudflats and/or salt marshes. Intertidal areas are of high ecological importance and trap sediments (sands, silts, clays and organic matter).
Within the Delft3D modelling package a large variation of coastal and estuarine physical and chemical processes can be simulated. These include waves, tidal propagation, wind- or wave-induced water level setup, flow induced by salinity or temperature gradients, sand and mud transport, water quality and changing bathymetry (morphology). Delft3D can also be used operationally e.g. storm, surge and algal bloom forecasting. 
 
On this discussion page you can post questions, research discussions or just share your experience about modelling coastal and/or estuarine systems with Delft3D FM. 
 

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Sub groups
D-Flow Flexible Mesh
DELWAQ
Cohesive sediments & muddy systems

 

 

Message Boards

Localazied overprediction of sedimentation

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Ali Abrishamchi, modified 8 Years ago.

Localazied overprediction of sedimentation

Hello,
The model overestimates sedimentation in certain cells as can be seen in the figure. This seems to be happened due to high bed shear stresses where sediment size is relatively fine (D50 of 1.5 mm). It is understandable to see erosion in that area due to the high bed shear stresses, however, the model keeps depositing in certain cells making the deposition to very high values. I appreciate any suggestions or comments to fix this.
Thanks,
Ali
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Pieter Koen Tonnon, modified 8 Years ago.

RE: Localazied overprediction of sedimentation (Answer)

hi Ali,

This is indeed strange behaviour which have not seen before. It is quite difficult to come up with suggestions as to how to solve this without more information. For instance, what is the grid resolution, time step, what are the initial depths in that area? How long are you running the model with what morphological acceleration factor etc? Can provide more information and please check the reference concentrations in time at the locations with high sedimentation, i suspect a numerical issue resulting in unrealistically (very) high concentrations at those locations (after which the sediment settles immediately)

As a quick fix, you could try to apply limiters on the wave height, reference concentrations and bed changes using the following keywords (either in mdf or mor file, depending on which version you use)

GamMax = 0.7
CaMax = 0.05
DzMax = 0.05

regards,
Pieter Koen Tonnon
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Ali Abrishamchi, modified 8 Years ago.

RE: Localazied overprediction of sedimentation

Hi Pieter,

Thanks a lot for your inputs and suggestions. I am going to incorporate those parameters and also look more closely to the issues you mentioned and will get back with more information. I appreciate your quick response.

Best regards,
Ali Abrishamchi