You need to create the region in the shallow water separate with deep water area. you also can create any regions, then insert the polygons and the define the maximum area as you like.

Hello Nguyen,

Thanks for your reply. Would you please explain more how to setup the multi grid size domain. Sorry, I am a new user.

Thanks,

Sham

Please read MESH Generator_Step by step. it will show you how to create the domains in Mike21.

Are you refereeing FM generator step by step or another manual.

Hi Sham, I think that if you are using the HD classic then you need to use the bathymetry generator and not the mesh generator. There needs to be a ratio for the cell size of 1 to 3 and the grid cells need to be multiples of 3. The last 10 years I have been using flexible meshes, butback when I was using the classic, I would generate the whole bathymetry with the finnest resolution (for instance 10m) covering the entire domain and then I would extract from it the 30m, 90m, 270m, 810m, etc. grids. But sometimes that takes too much space and time to generate the file. You can always create them independently, but don't forget the 3 to 1 rule! Also, before being able to run the nested grids, you need to smooth the borders, this is done with the MIKE 21 Toolbox. I hope you are already past this, but if not, I hope this works to push your work forward.