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

Boundary segment definition near the shore

SW
simon weppe, modified 7 Years ago.

Boundary segment definition near the shore

Youngling Posts: 14 Join Date: 3/28/12 Recent Posts
Hi All,

I am having some issues with some irrealistic longshore flows near the shoreline on both sides of my grid (flowing inside model domain on both sides). These flows appear on the outgoing tide and tend to dissipate with incoming tide. (I am using water level boundaries).

I was wondering about the best practice to define boundary segments along a grid side that includes an interface ocean-shore.
The "wet" portion of the grid side is split into several boundary segments, but how the should the interface ocean-land be handled ?

Some options :
-Use a (small) boundary segment that include the interface (i.e. 1 wet point and 1 dry point) and set boundary condition value to 0 (could be suitable for current boundary ? ).

-Use a (small) boundary segment that include the interface (i.e. 1 wet point and 1 dry point) and set boundary condition value to same as wet point on the dry point (could be suitable for water level boundary ?).

-Find the last wet point (accounting for highest tide level is simulation i.e. make sure) and use it as the end point.

I suppose a wrong setup can generate some incorrect water level gradients at these interfaces that could cause these kind of flows. I can actually see such small gradient near the shoreline but since I am using the setup 2 (from above), it should be linearly interpolated from identical boundary conditions values and so the same all along the segment.

Hope it is not too confusing !

Thanks
AA
Anonymous Anonymous, modified 7 Years ago.

RE: Boundary segment definition near the shore (Answer)

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

Is your FLOW model coupled to a wave model?

The most common way to define lateral boundaries, crossing land-sea interfaces, is Neumann boundaries. These type of boundaries define planform gradients. See if you model results improve by imposing a Neumann type of boundary along your lateral boundaries, with value to 0. Practically this means that the water level boundary will be instantly derived from your model result, based on the simulated water level just inside your model domain.

Good luck! Roderik
SW
simon weppe, modified 7 Years ago.

RE: Boundary segment definition near the shore

Youngling Posts: 14 Join Date: 3/28/12 Recent Posts
Thanks Roderik,

Yes, my FLOW model will eventually be coupled with a wave model.

The Neumann boundaries work perfect indeed, but I was just having some concerns about whether they were applicable or not given my model setup.(i.e open boundary north, neumann on sides, and mostly land south but with one river opening).

(see http://oss.deltares.nl/web/delft3d/coast-/-estuary/-/message_boards/view_message/275186, maybe I should have made one post really).

Thanks for the help !