Sediment yield assessment and suggesting mitigation measures—A case study of Deme watershed, Omo‐Gibe Basin, Ethiopia

Abstract

Soil erosion is a big challenge of natural resource development in Ethiopia due to the high expansion of agricultural activity and poor land‐use management. Deme watershed is one of the watersheds found in the Omo‐Gibe Basin, Ethiopia with soil erosion problems. It covers 1284.4 km2. The Soil and Water Assessment Tool (SWAT) integrated with ArcGIS was used to assess the sediment yield of the Deme watershed and develop mitigation measures for soil erosion. The purpose of this study was to assess the sediment yield and provide mitigation measures for the Deme watershed. Ground Control Point (GCP) data collection and field observation were conducted for land‐use land cover classification. The performance of the model was evaluated by coefficient of determination (R2), Nash Sutcliffe simulation efficiency (NSE), and percent bias (PBIAS). SWAT adequately reproduced the observed daily flows and sediment loads temporal evolution with R2 and NSE ≥ .7 and PBIAS < 15% both for the calibration and validation periods. The sediment‐rating curve measured an annual average suspended sediment yield of 12.79 tons per hectare per year, whereas the SWAT model predicted an annual average sediment yield of 14.35 tons per hectare per year. The spatial distribution map of sediment showed that 9 out of 17 sub‐watersheds generate a higher amount of sediment yield (15.1–45 tons/h/year) and are found to be erosion‐prone areas. For proper management of watershed terracing, filter strips, contouring, and reforestation scenarios were developed. Each scenario reduces the sediment yield by 74.29%, 58.34%, 47.78%, and 69.76%, respectively. The proper combination of these scenarios resulted in a 90% reduction in sediment yield. Policymakers and land‐use planners of different organization will benefit from this research by implementing soil and water conservation mechanisms and practices that strengthen and mitigate the natural systems of Deme watershed.