Watershed models play an important role in linking sources of pollutants to receiving waterbodies as nonpoint source loads. Watershed models are driven by precipitation, landuse, imprevious areas, slope, soil types and drainage area. GIS programs like BASINS and WCS provide the data that is needed for watershed models to predict both water and pollutant runoff from a watershed.
Another resource for learning more about models is EPA's Council for Regulatory Environmental Modeling (CREM). The CREM knowledge baseis continually updated and can be browsed by keywords or environmental indicators.
The following are seven commonly used watershed models used for watershed planning, estimating pollutant loads, and TMDL development - taken from EPA's Handbook for the Protection and Restoration of Our Waters (2008):