The grid used in the simulation of the sand transport rates and the rate of bed level changes is the same as that used to calculate the flow field using the hydrodynamic module, MIKE 21 HD. The wave grid may have the same grid spacing as the hydrodynamic one, or a smaller one.
The sand transport calculations will only be performed in the area where wave and current data exist, i.e. in the region common to the wave and the hydrodynamic grids. It should be checked that the area of interest for the sediment transport computations be covered by both grids.
The space resolution in the sand transport calculations is given by the spacing of the grid used for the hydrodynamic computations, so care must be taken that all the relevant details are covered when selecting the spacing of the hydrodynamic grid.
The grid spacing of the hydrodynamic grid (DxHD, DyHD) must be equal to or an integral multiple of the grid spacing used to determine the wave characteristics (Dxw, Dyw), both for the x-and the y- directions. The proportionality factors need not to be equal.
(5.27)
(5.28) 
