open TELEMAC-MASCARET The mathematically superior suite of solvers

I have conducted couple simulations (Telemac2D/Sisyphe) for sediment with d50 = 1 mm using van rijn equation (7).

1) Base case
Law of Bottom Friction = 5
friction coefficient = 0.0084
skin friction = 0

2) Convert Ks to Manning's roughness: n = 0.038 x ks ^ (1/6)
Law of Bottom Friction = 4
friction coefficient = 0.023
skin friction = 0

I found Case 2 (Manning) resulted in much less sediment movement than Case 1. I tested a range of Manning's n (0.01 to 0.035) and the results are similar to one and another. When I set skin friction = 1, the magnitude of sediment transport is similar to Case 1.

Does this have to do with how the model calculates the bed shear stress for Manning's and for Nikuradse?

Thanks.

Edwin

Hello,

This relation between ks and manning is an approximate relation. If you want to have the same exact friction coefficient, you should go back to their exact definition, as programmed in the friction_calc.f subroutine. Actually you should find that the relation between manning and ks should also depend on the local water depth. If you want more details, I can send you the relation you should use in an attachment

Good continuation, Cath