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

Problems with the salinity process

SS
Steven Sandbach, modified 7 Years ago.

Problems with the salinity process

Youngling Posts: 7 Join Date: 3/28/11 Recent Posts
Dear DELFT3D community,

I am having problems with my simulation - some of the computed salinity values are above the initial and boundary values.

The simulation includes River, Estuary and coastal region and the river discharge is large. At the start of the simulation I specify a uniform salinity in the model area and allow the fresh (0 salinity) river flow to flush the river and estuary region, because the river discharge is high - this takes a matter of 2-3 simulation days. The initial salinity is 33 ppt and at the sea boundaries I have specified a uniform salinity (of 33 ppt) coupled with a T-H time lag of 120 minutes. I have run the simulation in 2D and 3D (with 10 layers). In the 2D simulations, there is no problem but in the 3D simulations and predominately in the lowest layer (near bed), I produce salinity values >33 ppt. This occurs during ~ 2-3rd day where the fresh water of the river enters the coastal domain and persists for the rest of the simulation.

Has anyone encountered this issue before? I look forward to your response.

Regards

Steve
Arjen Luijendijk, modified 7 Years ago.

RE: Problems with the salinity process

Padawan Posts: 38 Join Date: 2/22/11 Recent Posts
Hi Steve,
Have you checked whether your computational time step is within the Courant criteria? You can use QuickPlot to do this when you have loaded a trim-file. Go to --> set file dependent options --> check time step - (press cancel). You will see three criteria popping up. Your flow velocities could become larger requiring smaller time steps to accurately resolve the salinities, and other constituents.

Hope this helps, Arjen
SS
Steven Sandbach, modified 7 Years ago.

RE: Problems with the salinity process

Youngling Posts: 7 Join Date: 3/28/11 Recent Posts
Dear Arjan,

Thanks for your message, however - I have already checked that so I'm not sure that is the solution. For the Courant condition, the area of the model domain that is most restrictive is further out into the ocean (into a deep canyon). The depths in this area are much larger than the mouth/near coast. I have looked at this condition via quickplot and the Courant conditions suggested minimum time step of just over 4 seconds. Some of the simulations I have conducted have time-steps of 3.75 and 1.875 seconds.

Thanks

Regards

Steve
Qinghua Ye, modified 7 Years ago.

RE: Problems with the salinity process

Jedi Council Member Posts: 610 Join Date: 3/2/11 Recent Posts
Hi Steve,

It is well-known that second or higher order advective di fference methods (such as the Cyclic method, used as the default in Delft3D-FLOW) on coarse grids may exhibit non-physical oscillations near regions of steep gradients. Did you check if the vertical Forester filter is on for 3D simulation?

If there is still problem, you may forwards this case to us and have a double check.

Regards,

Qinghua
SS
Steven Sandbach, modified 7 Years ago.

RE: Problems with the salinity process

Youngling Posts: 7 Join Date: 3/28/11 Recent Posts
Dear Qinghua,

Thanks for your response. Yes I have tried using the vertical forester filter and although it makes a difference to the salinity predictions, it doesn't prevent the salinity from overshooting. How should I send the files through?

Thanks for your assistance with this

Regards

Steve
Qinghua Ye, modified 7 Years ago.

RE: Problems with the salinity process

Jedi Council Member Posts: 610 Join Date: 3/2/11 Recent Posts
Hi Steve,

Yes, send me the input files by my email, qinghua.ye@deltares.nl pls if the files are not too big. Otherwise send me a message then I could arrange a ftp for you.

Regards,

Qinghua