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

Salinity for temporaries uncovered beds

OB
Olivier Boutron, modified 5 Years ago.

Salinity for temporaries uncovered beds

Youngling Posts: 3 Join Date: 3/25/14 Recent Posts
Dear all,

I'm trying to model water/salinity/temperature for en area with uncovered beds (Camargue, South of France). I have a TELEMAC model which is OK for water, but I have problems to model salinity and temperature.

The main problem is for salinity : for cells that can become wet or dry during the simulation, I obtain with Telemac unrealistic values (> 1000000g.L-1), when the water depth becomes very low. To solve this problem, I would need a model which consider the "solidification" of salt above a saturation value. Is it possible with DELWAQ to model salt solidification when the salinity is above a reference value? And is it possible to model the salt dissolution, when there is "solid salt" in a cell where the salt concentration in water is below the reference value (saturation value)?

I saw on the forum (post : "How does DELWAQ deal with sediment concentrations in cells that wet & dry?"), that if a segment is "dry" (depth below a given threshold), it is assumed no processes are taking place. In the case of salinity, is there a threshold, not on water depth, but on a maximum salinity value?).

I hope my questions are clear enough!

Olivier
Michel Jeuken, modified 5 Years ago.

RE: Salinity for temporaries uncovered beds

Jedi Knight Posts: 156 Join Date: 1/21/13 Recent Posts
Hi Olivier,

Welcome to the Delwaq forum. Currently there are no processes for Salinity in Delwaq at all, except advective and diffusive transport. It is also possible to model evaporation, which could be the only reason that you come to such high values. But a "solidification" is not yet possible. But since Delwaq is open source, you could add it yourself!

If no evaporation is in the model, and you still get these high concentrations then I think there must be something wrong in the mass balance. I don't know if Delwaq does any better on the TELEMAC flow results than TELEMAC itself, but you can easily try this out. Just make sure that the TELMAC output for Delwaq is genrated, and try to run Delwaq on these hydraulics.

greetings,
Michel
OB
Olivier Boutron, modified 5 Years ago.

RE: Salinity for temporaries uncovered beds

Youngling Posts: 3 Join Date: 3/25/14 Recent Posts
Dear Michel,

Thank you for this reply,

I forgot in my message to specify that we considered evaporation and rain (and wind), in the TELEMAC model, that' why we had such high values for salinity.

As I'm a new user of DELWAQ, I'm not aware the potential difficulties for implementing a threshold for salinity in the code. Do you think it can be performed easily ? (I've already developped things in FORTRAN for TELEMAC). A first approach for me would be to fix a maximum value for salinity (the mass balance will be wrong but it will avoid unrealistic values...)

Greetings,

Olivier
Michel Jeuken, modified 5 Years ago.

RE: Salinity for temporaries uncovered beds (Answer)

Jedi Knight Posts: 156 Join Date: 1/21/13 Recent Posts
Hi Olivier,

It shouldn't be very difficult to add an extra process to Delwaq if you have some programming experience, even if you would not have a lot of specific FORTRAN experience. You do need a FORTRAN compiler though, because Delwaq is programmed in FORTRAN. But we do have a special module, the OpenPLCT and a dedicated manual to guide you through the process to create an addtional dll that you can use next to the Delwaq executables to add extra user processes to it:

http://content.oss.deltares.nl/delft3d/manuals/D-Water_Quality_Open_Proc_Lib_User_Manual.pdf

With regard to your idea to limit the salinity concentration. You cannot change the concentration directly in Delwaq, you always calculate a flux that Delwaq has to apply to the mass. You can however calculate a flux of the surplus concentration above you maximum concentration (if there is any) and divided it by the time step (DELT in Delwaq). Define it with a stochio factor of -1 in relation to salinity (see manual for more explanation about this), and In the following time step, Delwaq will multiply this flux with DELT again, and deduct the surplus. Because transport is also calculated, you will not stay exactly at the maximum concantration, but sufficiently near it.


Good luck, and feel free to let us know if you managed to work it out!
Michel
OB
Olivier Boutron, modified 5 Years ago.

RE: Salinity for temporaries uncovered beds

Youngling Posts: 3 Join Date: 3/25/14 Recent Posts
Dear Michel,

Thank you very much for your help, I will follow your advices!

Regards,

Olivier
Michel Jeuken, modified 5 Years ago.

RE: Salinity for temporaries uncovered beds (Answer)

Jedi Knight Posts: 156 Join Date: 1/21/13 Recent Posts
Hi Olivier,

Your welcome. An as an extra tip: I just came around a similar process, the formation of viviante. It is described in the technical reference manual in 3.5, and the code is found in

.\src\engines_gpl\waq\packages\waq_kernel\src\waq_process\vivian.f

Good luck!

Michel