open TELEMAC-MASCARET The mathematically superior suite of solvers

Dear everyone,

In case of sediment mixtures (one sand and one mud class) and the use of Van Rijn formula for the equilibrium near-bed concentration, it is written in the user manual that zref = ks/2, where ks is the total roughness from the hydrodynamic steering file.

However, in the section about bed roughness predictor, in case of option 1, it is written that ks = ks' = alpha_ks * d50 where alpha_ks = 3.

I was wondering how ks was actually determined. From hydrodynamic steering file? And then how exactly? Or simply alpha_ks * d50?

I have difficulties to see how it is done in Sisyphe source code...

Thank you for your help.

Hi Olivier,
Without any specification, the total roughness coefficient is taken from the hydrodynamics file (Telemac-2d).
If you specify BED ROUGHNESS PREDICTION = YES (NO by default) and BED ROUGHNESS PREDICTOR OPTION = 1 (=1 by default), the roughness is computed as a function of the median sediment diameter d50 as ks=KSPRATIO \times D50, where KSPRATIO=3 by default and can be modified via the keyword RATIO BETWEEN SKIN FRICTION AND MEAN DIAMETER.

I hope it helps,

Cheers,

Pablo