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Hello,

I want to share some thoughts about the skin friction correction method for flat beds: SKIN FRICTION CORRECTION = 1

The correction factor mü = Cd'/Cd by means of the quadratic friction coefficients, as implemented in Sisyphe, is based on the Engelund method which divides the bed shear stress according to the energy slope. In fact, in terms of the Chezy coefficient C the above equation corresponds to mü = (C/C')^2. E.g. the Van Rijn formula uses this approach.

However some sediment transport formula like Meyer-Peter and Müller uses the Einstein method (division of hydraulic radius )for the determination of the grain shear stress which yields mü = (C/C')^1.5. In terms of the quadratic friction coefficients this approach yields mü = (Cd'/Cd)^0.75.

Therefore, compared to the original Meyer-Peter and Müller formulation, the approach implemented in Sisyphe gives too low sediment transport capacities. And the differences between the two approaches can be remarkable.

So I would propose to implement also the latter formulation into Sisyphe in order to get in line with the original Meyer-Peter and Müller formulation.

Maybe the simplest way is to check in tob_sisyphe.f which sediment transport formula the user has choosen...

I would be happy for any feedback or discussion.


Best regards,
Clemens

Hello Clemens,

Thank you for these explanations, it has been transmitted to the relevant experts for discussion and would be changes...

With best regards,

Jean-Michel Hervouet