Quantifying Soil Erosion and Identifying Critical Source Areas Under Current Management in the Holeta Watershed, Awash Basin, Ethiopia

Abstract

Erosion is the most widespread form of soil degradation overall in the world. In the current study, soil erosion is quantifed, and areas prone to high risk of soil erosion are identifed under current management in the Holeta watershed, Awash Basin, Ethiopia, where lands are primarily cultivated. The Soil and Water Assessment Tool (SWAT) was applied to simulate the baseline hydrologic and soil erosion processes. The model used spatial (i.e., DEM, land use, and soil maps) and temporal (cli mate) data to simulate diferent biophysical processes. Moreover, streamfow and sediment data were acquired and analyzed for model calibration and validation. The performance of the model during calibration and validation with both streamfow and sediment loads was evaluated against the measured data by using statistical parameters (R2 = 0.64, 0.81, NSE = 0.61, 0.76, PBIAS = 12.6%, 9.8%, respectively) during calibration and validation with streamfow and (R2 = 0.78, 0.68, NSE = 0.74, 0.61, PBIAS = 16.1%, 18.2%, respectively) while calibration and validation by sediment. The annual sediment load in the Holeta watershed varies from 2 to 136.4 t/ha/year with an average of 18 t/ha/year. The annual severity of sediment load was prioritized under very low, low, moderate, high, very high, and severe. About 13.3% of the Holeta watershed’s sub-basin contributed a higher sediment yield than average under current management. The signifcant sediment yield is generated from cultivated areas whereas; the lowest magnitude is generated from forested areas. Overall, since the generated sediment is within the tolerated range, current conservation retains soil loss for sub-basin 2, 4–15, and efective management practices can be identifed by further study and established for the erosion-afected areas (sub-basins 1 and 3)