Bed Roughness

The bed roughness parameter is used in MIKE 21 ST to relate the depth-averaged current velocity V to shear velocity U_f through

(5.5)   

where g is gravity and C is the Chezy number.

If the bed roughness has been expressed in terms of Manning numbers, they are internally converted to Chezy numbers through the relation

(5.6)   

where h is the water depth.

A value of bed resistance must assigned to every grid point in the model area. The bed resistance can be specified in two ways:

·         a constant value for all grid points

·         a map with a value for every grid point

If you specify the bed resistance by means of a map, the grid spacing and extent of the bed resistance data file must be the same as in the HD data file.

The specification of bed resistance for your MIKE 21 ST simulation must be consistent with the specification used in the hydrodynamic simulation that constitutes the basis for the sand transport calculation. Check the specifica­tion file for MIKE 21 HD if you cannot remember precisely the type and values of bed resistance used.