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Soil erosion, RUSLE, RMMF, Mountainous watershed of Nepal


Soil erosion is a crucial problem in Nepal where more than 80% of the land area is mountainous. In this study, two commonly used empirical soil erosion models, Revised Universal Soil Loss Equation (RUSLE) and Revised Morgan, Morgan and Finney (RMMF), were applied to the Kalchi Khola River Watershed of Nepal (drainage area approximately 58 hectares) to predict the soil loss rate and spatial erosion pattern. Models and field survey data were integrated using GIS tools. Several model runs were conducted to identify the most to least sensitive parameters of the models. On an annual basis, average soil loss rate predicted by the RMMF model for the watershed considered was found to be 3.76 tons per hectare (t/ha) over the agriculture land and 0.002 t/ha over the forested area. The RMMF model predictions are in close agreements with the available measured data of the region, whereas RUSLE predictions are far off, indicating that the RMMF model is a better choice to predict soil erosion rates in a steeply sloping mountainous region. It was also found that about 26% of the total watershed area is under high erosion risk (erosion rate > 5 t/ha per year). Moreover, about 60% of the area was found to be under high erosion risk if the entire watershed were converted into agricultural land. Accurate prediction of soil loss rates and erosion patterns will assist in the development of a robust soil conservation planning tool.