open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi everyone,

I review about critical shear velocity for mud deposition (cohesive sediment transport), I want to known the physical meaning and if there are average values. Also exists formula?, because I think 1000 (for default) is too much.

I atacched Krone's theory (1962)

Thanks

Hi,

This keyword represents the shear velocity value under which deposition occurs. You can have a look to the user manual (sections 6.1 or 6.4.2).
You're right, a default value of 1000m/s is large, but always allows the deposition (deposition flux then computed as settling velocity times mud concentration according to the Krone/Partheniades formula) which will mainly be instantaneously re-suspended according to the associated critical erosion shear stress (lower). This why this usual "large" value is set by default.

You can find a lot of literature on this topic.

In a first approach, you can see it in the same way that for the erosion:
Shear velocity is computed as sqrt(shear_stress/rho_eau).
Critical values of shear stress roughly range from 0.1 N/m2 (for fresh deposit) to 1 N/m2 or more (for consolidated mud) that lead to critical shear velocities of a few cm/s.

Regards,
Laurent

Hello,
I complete a bit on the top on Laurent's nice comments.
This kind of "trick" can be found in the literature under the name of "paradigms". For example, approaches like "exclusive" or "simultaneous" paradigms are commonly used when modelling mud applications. Exclusive approach means that erosion and deposition do not occur at the same time, while simultaneous paradigms allows erosion and deposition to occur at the same time.
Classical references by Winterwerp and van Kesteren (2004) or Winterwerp (2006) can shed more light on this topic.

Cheers,
Pablo