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Dear all

Can anyone please help me with the units for the Coefficient of Friction? The default value is 50 but what is the unit?
I seem to remember that a earlier version of T2D (v5.1 or earlier?) used the Nikuradse roughness length as the CF? Is this still valid?

Thanks
John

Hello,

The dimension depends on the chosen friction law. The value 50 corresponds to a Strickler law, it has dimension m**(1/3)/s, Chézy coefficient has dimension m**(1/2)/s, Nikuradse coefficient is in metres, etc.
With this coefficient a dimensionless coefficient CF is then computed.

With best regards,

Jean-Michel Hervouet

Thanks - that makes sense - I have previously used Nikuradse and used Ks in metres.
John

Dear Jean-Michel

One further clarification please.
I believe that when I apply a spatially varying coefficient via strche.f, I need to omit the relevant keywords from the steering file.
How is the appropriate law of bottom friction specified to the model in this case?
John

Hello,

Actually not. The keyword on spatially varying coefficient is no longer used and STRCHE is systematically called (see subroutine fonstr.f in library bief). So you need not remove any keyword about friction in your steering file, your strche.f will supersede them all (just keep in mind that if you change the friction law you will have to change the values in strche accordingly).

With best regards,

Jean-Michel Hervouet