Predicting Runoff, Sediment and Management Scenarios for Reducing Soil Erosion in Data Scarce Regions, Blue Nile Basin

This study presents modeling runoff and sediment with management scenarios for watershed management and resource erosion in Koga watershed using AnnAGNPS model. Calibration of the model was carried from 1988–2001 and validation from 2002–2007. The result of sensitivity analysis indicated that the CN was the most sensitive parameter to runoff and peak runoff rate whereas LS and K-factor were for sediment yield following RF, and these parameters were subjected to calibration. For model calibration, R of 0.69, 0.35, 0.55; NSE of 0.69, −0.38, 0.55; RSR of 0.54, 1.14, 0.67; and PBIAS of 0.07%, −80.56% and 4.09% were obtained for surface runoff, peak runoff rate, and sediment load, respectively. Similarly validation results indicated an R of 0.76, 0.54, 0.62; NSE of 0.76, 0.38, 0.62; RSR of 0.43, 0.71, 0.56, and PBIAS of 2.31%, −36.58% and 5.68% for surface runoff, peak runoff rate, and sediment load, respectively. Where the model efficiency was rated at the range of fair to excellent for three of the outputs of the model for both calibration and validation period. Only 21.5% of the area was able to generate the 78.8% of total soil erosion, with higher than tolerable limit. Hence converting of 21.5% of highest eroding cropland cells either to forest or grassland would reduce soil erosion, sediment yield and load significantly. Ultimately it would help to reduce the sedimentation in Koga dam which could result in reduction of storage capacity.