cheapaml_BulkCdn = cdrag_1/usm + cdrag_2 + cdrag_3*usm
ustress(i,j,bi,bj)= rhoa*cheapaml_BulkCdn*uss*uw
vstress(i,j,bi,bj)= rhoa*cheapaml_BulkCdn*uss*vw
_RL cheapaml_BulkCdn