open TELEMAC-MASCARET The mathematically superior suite of solvers

Dear everyone,

We are testing a 3D mud transport model. We use the SEDI-3D module inside Telemac-3D for sediment transport.

Currently we found the sedimentation on the intertidal area (near the banks of the upstream river) is too much. A closer look at a node on the tidal flats shows a strange behaviour.



The erosion flux is always remains negligible because the flow is relatively slow and we also set THRESHOLD FOR SEDIMENT FLUX CORRECTION ON TIDAL FLATS = 0.1m. The deposition flux is large when there is water, and it becomes zero when this node gets dry, which is logical.



However, when we look at the concentration at his node, it is confusing. The concentration decreases when the water depth decreases. But it goes up and stay in a certain level when this node is dry. Since there is no water at those moments and no erosion, we don't know why the concentration increases.



Then we also compare the bed shear stress with the water depth. There are peaks during the dry period but I think this is due to the numerical instability when the water depth is very very small. It still doesn't explain why there is concentration during the dry period.

I attached my steering file here in case there is something wrong in my settings.

Does anyone happen to know how to revolve this issue?

Best regards,
Qilong

Hi Qilong,

I'm not an expert of SEDI-3D but I had the same issue with the v7p0r1.
By discussing with SEDI-3D users, it seems that the current version of TELEMAC-3D,and especially SEDI-3D, is not able to deal with dry nodes/tidal flat. May this will be fixed in the next version.
I didn't have enough time to get in SEDI-3D modules to understand correctly where and what is the main problem.
I was still able to run my model proprely by cutting my model with as criterion a height of water even if this is not mass conservative.
May be, this year, we will (or at least I will focus during my personal time) focus on this problem, may we can share our results ?
Best regard,
P.N

Thanks for the reply!

Indeed I have a feeling that the drying/wetting for the sediment transport is not as sophisticated as in the hydrodynamic module.

Except for the inter-tidal areas, we could get reasonable sediment concentration in relatively deep channels and nice spatial patterns of sediment movements.

Look forward to the future improvements in SEDI-3D.

Best regards,
Qilong