They have models for run off. In my previous career we used tr55 analysis of watersheds, this included surface types, slopes and areas. You model for various

They have models for run off. In my previous career we used tr55 analysis of watersheds, this included surface types, slopes and areas. You model for various storms once the model is built. We didn't have to deal with mountain snow packs which add another factor. Edit: I think newer programs to model exist now. Some are here https://www.nrcs.usda.gov/wps/portal/nrcs/detailfull/national/water/manage/hydrology/?cid=stelprdb1042480 https://www.nrcs.usda.gov/wps/portal/nrcs/detailfull/nationa... 165 page PDF describes it. https://www.hydrocad.net/pdf/TR-55%20Manual.pdf https://www.hydrocad.net/pdf/TR-55%20Manual.pdf