SURFACE RUNOFF AND SOIL EROSION ESTIMATION USING THE SWAT MODEL IN THE KELETA WATERSHED, ETHIOPIA

This study evaluates surface runoff generation and soil erosion rates for a small watershed (the Keleta Watershed) in the Awash River basin of Ethiopia by using the Soil and Water Assessment Tool (SWAT) model. Calibration and validation of the model was performed on monthly basis, and it could simulate surface runoff and soil erosion to a good level of accuracy. The simulated surface runoff closely matched with observed data (derived by hydrograph separation). Surface runoff generation was generally high in parts of the watershed characterized by heavy clay soils with low infiltration capacity, agricultural land use and slope gradients of over 25 per cent. The estimated soil loss rates were also realistic compared to what can be observed in the field and results from previous studies. The long-term average soil loss was estimated at 4.3 t ha(-1) y(-1); most of the area of the watershed (similar to 80 per cent) was predicted to suffer from a low or moderate erosion risk (<8 t ha(-1) y(-1)), and only in similar to 1.2 per cent of the watershed was soil erosion estimated to exceed 12 t ha(-1) y(-1). Expectedly, estimated soil loss was significantly correlated with measured rainfall and simulated surface runoff. Based on the estimated soil loss rates, the watershed was divided into four priority categories for conservation intervention. The study demonstrates that the SWAT model provides a useful tool for soil erosion assessment from watersheds and facilitates planning for a sustainable land management in Ethiopia. Copyright (C) 2010 John Wiley & Sons, Ltd.