Soil Erosion Risk Assessment Using GIS Based USLE Model for Soil and Water Conservation Planning in Somodo Watershed, South West Ethiopia

Abstract

Soil erosion is natural phenomena and is modified by biophysical environment comprising soil, climate, terrain, ground cover and their interactions. Due to different factors, it is difficult to make watershed management successful in all areas at one time. Because of this, prioritization of sub watershed is very important for soil conservation planning and implementation. In Somodo watershed more than five years different soil and water conservation technologies were implemented and satisfactory result was not recorded. In this aspect, it is important to consider further watershed management planning., This study therefore investigated soil erosion risk assessment using GIS and USLE model for soil and water conservation in Somodo watershed southwestern Ethiopia with the aim of estimating soil erosion rate and identify soil erosion hot pot areas through prioritization of sub watershed in Somodo watershed by the help of GIS based USLE model. Both primary and secondary data sources were used for model input. These data were computed at a grid level with 30*30m resolution and then overlaid to generate mean annual soil loss by the help of raster calculator in Arc GIS tool. Results of the study showed that, the mean annual soil loss of the watershed was 18.69 ton ha-1 year-1 ranging from 0 to 131.21. More than 75% of the watershed have soil loss greater than 20 ton ha-1 year-1 and only 25% of the area have soil loss ton ha-1 year-1.On the bases of mean annual soil loss SW-4, SW-6 and SW-7 were under slight (0-10 ton ha-1 year-1) erosion severity level, while the remaining SW-2, SW-3 and SW-8 were under moderate (10-20 ton ha-1 year-1) level. And SW-1 was in high (20-30 ton ha-1 year-1) erosion severity level, where as SW-5 and SW-9 were found in very high ( ton ha-1 year-1) erosion severity level. Since large area of the watershed has soil loss more than tolerable level (11 ton ha-1 year-1) attention should be given to identify erosion hot spot areas to minimize the on-site and off-site problems. Therefore, the study suggested that for effective watershed management and soil conservation planning, these sub-watershed priorities should be used in the watershed.