open TELEMAC-MASCARET The mathematically superior suite of solvers

Dear everyone,

This is more a question about sedimentology rather than Sisyphe, but maybe some of you have some experience on the subject.

I am studying cohesive sediment dynamics in an intertidal area with 2D depth-averaged model Telemac2d + Sisyphe). The erosion rate E is computed using the Partheniades formulation:

E = M * (tau/tauc - 1) if tau > tauc

where M is the Partheniades parameter, tau is the bottom friction and tauc is the critical bottom friction for erosion.

Whatever the bottom friction formulation we use, it is a function of H^(-alpha), where H is the water depth and alpha is strictly positive. As I am studying intertidal wetlands with flooding and drying happening all the time, the bottom friction could be very high when the water depth is very small, even for small velocities, which is probably not very physically accurate, leading to very high, unphysical erosion rates.

I was considering two approaches to deal with that issue:

1) The factor (tau-tauc - 1) could be seen as a probability of erosion and therefore should be limited to values between 0 and 1. I tried it, and it leads to more reasonable erosion rates at low water depth.

2) Prevent erosion when water depth is smaller than a threshold value.

If some of you have some experience on the matter, I would be very happy if he or she can share it with me

Hello Olivier,
Your approach 2 seems to be reasonable and physically based. It could be great if you can test it to see how your model behaves.

I think I've seen something related with the approach 1 in the literature. I'll take a look and let you know if I found something.

Best wishes,

Pablo

Hi Olivier & Pablo,

In 3D there is a keyword to limit erosion fluxes on intertidal areas.

'THRESHOLD FOR SEDIMENT FLUX CORRECTION ON TIDAL FLATS'

You can use this to limit erosion fluxes - still deposition is allowed on tidal flats -

In Siysphe I think that you can use the keyword
MINIMAL VALUE OF THE WATER HEIGHT
The water depth is limited and velocities are set to zero which should give a zero erosion flux.

Hope this helps,

Cath

Thank you Catherine. It is indeed the use of "MINIMAL VALUE OF THE WATER HEIGHT" that works the best in my case. At least better than the two suggestions I made in my first post.