I just wanted to ask if using HEC-RAS Rain-on-Grid approach a good alternative for a hydrologic study of an area as compared to the usual modelling using HEC-HMS?
HEC-RAS Rain on Grid can be a good alternative to HEC-HMS. However, it does require more detail 2D mesh, including if you have any structures like bridges and culvert you want to incorporate.
In general, HEC-HMS should be used for hydrology and leave the hydrualic analysis for HEC-RAS. However, that gap is beginning to narrow with Rain on Grid and Infiltration option in HEC-RAS.