Erosion Source Area Identification Using Rusle and Multi-criteria Decision Analysis, Acase of Andassa Watershed, Upper Blue Nile Basin

Abstract The Main objective of this study was to identify source areas of soil erosion and quantify rate of soil erosion and sediment yield in Andassa watershed, Blue Nile Basin. In this study, Multi Criteria Decision analysis (MCDA) technique integrated with GIS and Remote sensing was applied to estimate soil erosion source areas, identify major soil erosion factor (s), prioritize and map the most sensitive soil erosion sources of the watershed for soil and water conservation practice. From soil erosion factors, Topographic wetness index followed by land use land cover have been found to have significant effect on soil erosion in the watershed. The result shows in qualitative Sensitivity map investigates that the more than half of the watershed was under moderately sensitive risk of soil erosion (68.12%) about 400.861km2. Next 17.56% (103.35km2) of the watershed was under slightly sensitive and the remaining 14.27% (83.999 km2) of the watershed was under highly sensitive risk of soil erosions. From the overall combined map of Multicriteria decision analysis (MCDA) map showing the areas of increased risk erosion represented by highly sensitive (S1), moderately sensitive(S2), less sensitive(S3), and constraint areas so the governmental or non-governmental organizations or any concerned organization should refer this important severity map of soil erosion for watershed management and priority of the watershed. Even though measured values of sediment yield at the catchment are hardly available the hotspot areas can be identified by multicriteria decision analysis and significant amount of soil loses are sourced from Gully sites.