Identifying Soil Erosion Risks for Planning of Watershed Management: The Case of Weyib Watershed, Southeast Ethiopia

Identification and prioritization of erosion-prone watersheds have remarkable significance for planning of conservation schemes at the sub-watershed level, as it is too costly to enforce watershed development structures on the whole watershed at a time. Hence, the prime objective of the study is identifying and ranking of erosion-risk regions of the Weyib watershed, situated at the Genale-Dawa basin in Ethiopia. The watershed covers an area of 3973 km2 with a basin length of 369 km. Morphometric analysis and RUSLE models have been used with the aid of arc GIS and remote sensing techniques to identify and map erosion-risk areas. The morphometric assessment involved both linear and shape parameters through the compound parameter ranking approach while RUSLE parameters like rainfall erosivity, soil erodibility, slope steepness and length, land cover, and management activities have generated from their respective datasets and overlaid to quantify potential soil erosion. The result of the morphometric analysis revealed that SW-3 (sub-watershed), SW-4, SW-7, and SW-8 necessitated urgent interventions. On the other hand, the results of RUSLE estimated the mean annual rate of soil loss as 27.77t/ha/year, that is beyond the tolerable limit of 10t/ha/year. Based on this value, SW-7 and SW-8 are categorized as high erosion-prone areas. Hence 224.8 km2 area of the watershed is labeled under high erosion risk area. Sensitivity analysis result indicated that RUSLE is more sensitive to cover and topographic factors in the watershed. The overall result of the two models specified that the lower part of the watershed demanded prime attention. Thus, the government has to reinforce the watershed development endeavors initiated by focusing on high erosion susceptible sub-watersheds in the Weyib watershed.