Ethiopian highlands have been increasingly exposed to the risk of soil erosion and evaluations of how various management practices can reduce the risk of soil erosion are still limited. Here, the calibrated and validated Soil and Water Assessment Tool (SWAT) is used to estimate soil loss rates, identify erosion hotspot areas and evaluate effective best management practices (BMP) to curb the risk of soil erosion. The annual sediment yield (SY) in Toba watershed varies from 0.09 t ha-1 yr-1 to 44.8 t ha-1 yr-1 with an average SY of 22.7 t ha-1 yr-1. Cultivated lands on steep slopes are the sources of extensive soil loss rate, whereas areas with good vegetation cover have low SY. The increased population pressure, increased cultivation of steep slope and uncontrolled grazing are the causes of high SY in the watershed. 17 sub-basins with SY higher than the tolerable erosion of Ethiopia (2-18 t ha-1 yr-1) are considered for the application of BMP scenarios. Implementing all BMPs could reduce the extent of SY but with varying degrees and combination of the BMPs are more pronounced and desirable. Reforestation with vegetative strips was the most effective management (87.8% reduction) followed by soil/stone bund with vegetative strips (83.7% reduction). These findings are important to ensure sustainable land management and promote sustainable agricultural production in a rapidly changing agricultural watershed. In general, the result highlights the need for regional developments and cooperation to urge for strong BMPs strategies for the rapid land and water resources degradation.

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Land degradation caused by soil erosion has become the most serious problem in the Ethiopian highlands. Quantifying the spatial variations of soil loss with a strong evidence helps to prioritize the watersheds for the implementation of different management practices. The study was carried out in the Toba Watershed of the Upper Blue Nile Basin in Ethiopia. Its objective was to evaluate the rate of soil erosion and identify the hotspots with high risk of soil erosion for watershed management planning. Then, Soil and Water Assessment Tool (SWAT) was used to evaluate the effectiveness of best management practices (BMP) in reducing soil loss. The performance of SWAT in simulating streamflow and sediment yield was evaluated through sensitivity analysis, uncertainty, calibration and validation process. Statistically, the calibrated and validated sediment yields (SY) against the observed sediment data were reasonably accurate (R2 = 0.67, 0.65, NSE = 0.66, 0.64, PBIAS=-8.4%, 9.8% respectively). The annual SY in Toba watershed varies from 0.09 t ha− 1 yr− 1 to 44.8 t ha− 1 yr− 1 with an average SY of 22.7 t ha− 1 yr− 1. To prioritize the SY of the watershed, the annual severity of SY was divided into six classes: very low, low, moderate, high, very high and severe. The study also showed that SY in most watersheds (about 53.8%) were higher than the average. Cultivation on steep slopes leads to the highest SY, while forested areas have lower SY contribution. five management scenarios were evaluated using the Calibrated model. Seventeen sub-basins with SY exceeding the tolerable erosion of Ethiopia (t ha− 1 yr− 1) were considered for the analysis of the BMP scenario. The results show that reforestation combined with vegetative strips was the most effective for soil erosion control (87.8% reduction) followed by the combination of soil/stone bund and vegetative strips (83.7% reduction). Overall, the results of this study provided important data for watershed management and are very useful to ensure the sustainable management of land and natural resources at watershed level.

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