ESTIMATING SOIL LOSS FOR SOIL CONSERVATION PLANNING IN AFA RIVER WATERSHED OF UPPER BLUE NILE BASIN, NORTH WEST ETHIOPIA

Abstract

Soil erosion is a worldwide problem that cause environmental degradation. The problem is severe in African countries including Ethiopia. Afa river watershed is also the victim of this problem. This study was aimed to estimate soil loss in the watershed by GIS based USLE model, and prioritize sub watersheds for soil conservation planning. Primary and secondary data for the study were collected from different sources and used for the estimation of USLE model parameters. Rainfall erosive effect, soil erodibility, topographic effect, land use land cover and supportive conservation practice factors were used as an input for the model to determine the amount of soil loss from the watershed. A combination of GIS application, Remote Sensing technique, and USLE model were used for soil loss estimation and the result showed that the annual soil loss from the watershed was in the range of 0 to 129.578 ton ha-1 year-1 with mean soil loss of 20.039 ton ha-1 year-1.The mean soil loss, 20.039 ton ha-1 year-1, was greater than soil loss tolerance of 11ton ha-1 year-1. Based on mean annual soil loss and erosion risk area coverage, erosion 'hot spot' areas were identified and prioritized for conservation planning. Accordingly, SW5, SW 15, SW 17, SW 14, SW 13, SW 6, SW 2, SW 10, SW 7, SW 11, SW 8, SW 18, SW 19, SW 1, SW 4, SW 9, SW 16, SW 3 and SW12 got 1 up to 19 priority level respectively. This study recommended that soil and water conservation measures should be planned for impelimentation, starting from SW5 to SW12 based on the capacity of logistics, time, budget and skill availability.