GIS based distributed model for soil erosion and rate of sediment outflow from catchments

A spatially distributed rainfall-runoff-soil erosion model capable of handling catchment heterogeneity in terms of landuse, soil, slope, and rainfall has been developed and applied to data from several catchments. The model operates on a cell basis and accepts distributed inputs from a raster geographic information system (GIS). The catchment digital elevation model is used in the model to generate drainage paths from each of the discretized cells to the catchment outlet in proper hydrologic order. Following the computational hydrological sequencing thus derived, the mechanics of overland flow are modeled using a finite volume based numerical solution of the diffusion wave approximation of the St. Venant equations and the process of soil erosion is modeled using a numerical solution of the sediment continuity equation with appropriate auxiliary equations. The spatial information for each cell of the catchment was generated using digital analysis of satellite data and published information by making use of commercially available image processing and raster GIS packages. Results of model application on several catchments indicate that the model can compute temporal distribution of the sediment outflow rate at the catchment outlet for storm events reasonably well. The cell-based structure of the model also allows for computation of the spatial distribution of computed variables such as the amount of soil erosion.