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. 




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



Message Boards

Sediment accumulation near boundaries

Shawn Harrison, modified 8 Years ago.

Sediment accumulation near boundaries

Padawan Posts: 70 Join Date: 6/25/12 Recent Posts

I'm curious if there is a way to avoid sediment accumulation near an open boundary (In FLOW-WAVE-SED simulations)?
For example, is it possible to specify a region within which sediment is permitted to settle (or alternatively a region where it is not permitted to settle)?

Also, when running waves on a grid where depths along the boundary are non-uniform and while specifying a uniform wave condition along that boundary, it is possible that waves break due to depth-limitations... is it possible to apply a buffer along the first few rows along a boundary to avoid wave-breaking-induced currents? I'm aware that the appropriate thing to do would be to nest the domain in a larger wave grid so that suitable wave conditions are applied to the flow model domain.. just hoping that maybe there is a shortcut for quick and dirty purposes.

Thanks for sharing your experience,
Anonymous Anonymous, modified 8 Years ago.

RE: Sediment accumulation near boundaries

Jedi Master Posts: 333 Join Date: 7/30/20 Recent Posts
Hi Shawn,

If you are working with cohesive fractions (Patheniades, 1965) you can define spatial varying 'critical bed shear stress for sedimentation'. Put it at zero in the region where you do not want to permit sedimentation.

Regarding your questions about the wave boundary conditions, in general it is not recommended to define wave boundaries anywhere you expect a feedback on your wave physics, whether it is bathymetry or hydrodynamics induced, unless you are confident that this is properly incorporated in your boundary conditions. You could artificially suppress wave-induced currents, e.g. by locally defining a very high roughness or viscosity, just like you do for imposing space-varying critical bed-shear stress for sedimentation. This is at your own risk!

Good luck

Cheers, Roderik
Shawn Harrison, modified 8 Years ago.

RE: Sediment accumulation near boundaries

Padawan Posts: 70 Join Date: 6/25/12 Recent Posts
Thanks for the tips Roderik. I will see how they work.
Andrew Stevens, modified 8 Years ago.

RE: Sediment accumulation near boundaries

Youngling Posts: 11 Join Date: 4/25/11 Recent Posts
Hi Shawn,

I had a case where I was imposing large sediment sand concentrations on a river discharge boundary and this was leading to the boundary closing off and model instabilities. In order to maintain stability, I used dredging and dumping to move the sediment a few grid cells away from the boundary (I also increased the erosion factor for dry cells). Although the dredging and dumping sounds a bit strange, it worked well with my model configuration. Just an idea.