Abstract:
Land degradation by soil erosion is a wide spread and serious phenomenon throughout the Ethiopian highlands causing significant loss of soil fertility, loss of productivity and environmental degradation. Thus, estimation of soil loss and identification of critical area for implementation of best management practice is central to success of a soil and water conservation program. This research has, therefore, been carried out to evaluate soil erosion risk in the study area so as to estimate the rate of soil loss and identify areas prone to high erosion risk using RS and GIS techniques, to specify the major factors affecting the erosion development in the study area, to develop soil loss intensity maps of the study area and to prioritize areas for specific soil conservation plan. The research integrates the Revised Universal Soil loss Equation (RUSLE) with satellite remote sensing and geographic information system (GIS) as a useful tool for conservation planning. Soil loss estimation was carried out based upon the principles defined in the RUSLE, which relates soil erosion process to rainfall erosivity, soil erodibility, topographic factors, and land cover and conservation practices. The input parameters of the model, derived from GIS analysis of primary data, were compiled in GIS database in raster data model with grid resolution of 30 meters. The spatial thematic map of the respective factors of RUSLE was created as follows: R factor map was interpolated from point data of stations; K factor map by reclassification of soil map; LS factor (relief parameters) was derived from Digital Elevation Model (DEM); C and P factor map by reclassification of landuse/land-cover map of Landsat ETM+ (Enhanced Thematic Mapper Plus) image. Raster calculator was used to interactively calculate annual soil loss and prepare soil erosion risk map. The result showed that the average annual loss of the district ranges from 0.00 to 369.2tons/ha/yr and the mean annual soil loss rate is 7tons/ha/yr. Moreover, the total soil loss in the study area was 8,271,475.58 ton from 22403.78 hectares. Based on the level of soil erosion rates, the study area was divided into five priority categories for conservation interventions. Accordingly, Yerim kebele, central part of Sheshamba, parts of Ento Lafto Lenqa, Haqgela, Senfe, Bealagela, Ambicho Beyleya and Wogila are Kebeles with the highest soil loss in the study area. Based on the analysis, soil loss on about 73.24% (16408.78 hectare) of the district was categorized very slight to slight class which under SLT values ranged from 5 to 11 tons per hectare per year. The remaining 26.76% (5995 hectare) of land was classified under moderate, severe and very severe class about several times higher the maximum tolerable soil loss. Higher soil losses rate were detected in areas where the following major factors are combined: heavy rains, soils without conservation practices with little vegetation cover and convex topography having high LS-factor value. As a result, these critical kebeles need to be prioritized based on their average annual soil loss rate for future intervention of soil and water conservation measures