Spatially Distributed Modeling of Soil Erosion and Sediment Transport at Watershed Scale

A distributed, physical and GIS-based modeling approach is developed to estimate runoff, soil erosion by water and sediment transport within a watershed at a daily time step. The approach relies on the use of GIS data for deriving major model parameters that show distinct spatial variability over the catchment. Surface runoff is calculated by a modified rational method, which depends upon rainfall intensity, soil moisture status, slope, land-use, and soil characteristics. The erosion model simulates soil erosion by raindrop impact and shear erosion in overland and channel flow using equations with a physical basis. A diffusive approximation method is used for routing runoff and sediment transport to the basin outlet. The model uses as few parameters as possible while retaining its physical basics. The model was applied on the Latyan dam catchment in Alborz mountain range in the northern part of Iran. Simulated river discharge and sediment concentration are compared to daily measured data from September 2005 to September 2006. The results indicate that there is a good agreement between simulated and measured discharge and sediment concentration at the basin outlet, though more efforts regarding soil erosion and sediment transport need to be clarified by further research.