Estimation of sediment yield and areas vulnerable to soil erosion and deposition in a Himalayan watershed using GIS

Erosion is a natural geomorphic process occurring continually over the earth's surface and it largely depends on topography, vegetation, soil and climatic variables and, therefore, exhibits pronounced spatial variability due to catchment heterogeneity and climatic variation. This problem can be circumvented by discretizing the catchment into approximately homogeneous sub-areas using Geographic Information System (GIS). In this study, the remote sensing and GIS techniques (through ERDAS Imagine 8.6 and ArcGIS 9.1 software) were used for derivation of spatial information, catchment discretization, data processing, etc. for the Himalayan Chaukhutia Watershed (India). Various thematic layers for different factors of Universal Soil Loss Equation (USLE) were generated and overlaid to compute spatially distributed gross soil erosion maps for the watershed using 18-year rainfall data. The concept of transport limited accumulation was formulated and used in ArcGIS for generating the transport capacity maps. Using these maps, the gross soil erosion was routed to the catchment outlet using hydrological drainage paths for the derivation of transport capacity limited sediment outflow maps. These maps depict the amount of sediment rate from a particular grid in spatial domain and the pixel value of the outlet grid indicates the sediment yield at the outlet of the watershed. Upon testing, the proposed method simulated the annual sediment yield with less than +/- 40% error.