STREAM FLOW AND SEDIMENT YIELD MODELING: THE CASE OF ROBI JIDA WATERSHED, UPPER BLUE NILE BASIN, ETHIOPIA

Abstract

Soil erosion, streamflow, and sediment studies are crucial for supporting the agricultural sector through watershed planning and management practices. This study aimed to model stream flow and sediment yield in the Robi Jida watershed in the Upper Blue Nile Basin, Ethiopia, and identify best management scenarios with the records of suspended sediment concentration. The historical records of the meteorological, hydrological, and suspended sediment concentration data were used for the hydrological modeling. Sediment yield data was generated from the discharge-sediment rating curve equation using the suspended sediment concentration data. Spatially, 30*30 m DEM, 90*90m soil, and 30*30m resolution land use/land cover data were used as input for the hydrological model. In this study, the Soil and Water Assessment Tool (SWAT) model was used to model streamflow and sediment yield. The model performance in simulating streamflow and sediment yield was evaluated through sensitivity analysis, calibration, and validation processes. Period from 1994 to 2010 was used for calibration and 2011 to 2018 was used for validation. During calibration the model performance statics R2 , NSE, and PBIAS were obtained (0.80, 0.70), (0.80, 0.70), and (-4.8, 1.1) for stream flow and sediment yield respectively, and similarly for model validation R 2 , NSE, PBIAS as obtained (0.77, 0.72), (0.77, 0.71), (-4.7, -5.7) respectively. Therefore, the result indicated that the SWAT model performed well and the estimated average annual sediment yield of the Robi Jida watershed was 6.42 tons/ha/year. Based on the average annual simulated sediment yield, identified 9 sub-watersheds are critical whose annual sediment yield limit ranges above the tolerable limit were identified and prioritized for effective watershed management. Therefore applying and evaluating the different management scenarios, filter stripe 1m and 5m, vegetative contour strip, soil/stone bund, terracing, and contouring resulted in a 19.15%, 35.01%, 47.13%, 57.09%, 73.37%, and 52.81% decrease in the average annual sediment yield, respectively. Therefore, soil/stone bund and terracing scenarios demonstrated the highest potential for reducing sediment yield and showed promising results as effective best management practices in the Robi Jida watershed.