ABSTRACT: The two-dimensional soil erosion model CASC2D-SED simulates the dynamics of upland erosion during single rainstorms. The model is based on the raster-based surface runoff calculations from CASC2D. Rainfall precipitation is distributed in time and space. Infiltration is calculated from the Green-Ampt equations. Surface runoff is calculated from the diffusive wave approximation to the Saint-Venant equations in two-dimensions. Watershed data bases in raster Geographical Information System (GIS) provide information on the soil type, size fractions, soil erodibility, cropping management, and conservation practice factors for soil erosion calculations. Upland sediment transport is calculated for the size fractions (sand, silt, and clay), and the model displays the sediment flux, the amount of suspended sediment, and the net erosion and deposition using color graphics. The model has been tested on Goodwin Creek, Mississippi. The peak discharge and time to peak are within ± 20 percent and sediment transport rates within −50 percent to 200 percent.