ESTIMATING SURFACE RUNOFF AT WEYIB SUB-WATERSHED, GENALE DAWA RIVER BASIN, ETHIOPIA

Abstract

A systematic assessment of water potential of a country is vital in engineering planning, environment, impact assessment, water balance calculation and utilizing water source in a sustainable manner. But one of the challenge in Ethiopia including Weyib sub-watershed outlet at Denbel was lack of accurate information on the spatial distribution of surface runoff yield generated from each sub basins. Agarfa Small Scale Irrigation project sub-basin was one part of the study area which had not accurate surface runoff information. The estimation of surface runoff yield for Weyib sub-watershed by using SWAT model lessened this challenge. Spatial and climatic data were the inputs of the model. Sensitive runoff parameters were automatically calibrated and validated by using SWAT-CUP model and a statistical model efficiency of R2 = 0.87 and 0.86 and ENs = 0.78 and 0.71 was found for calibration and validation period respectively. The twenty nine (1986 to 2014) year average monthly and yearly estimated surface runoff yield of twenty five sub-basins in in Weyib sub-watershed were 6.65 mm and 79.38 mm respectively. From the twenty five sub-basins identified in the study area, sub-basin one was delivered highest surface runoff and sub-basin twenty four was delivered the smallest surface runoff yield with annual surface runoff yield of 11.14 and 0.07 mm respectively. But the contributed surface runoff yield was rated with their respective area, sub-basin five was delivered highest and sub-basin twenty five was delivered smallest by producing annual surface runoff yield of 1.90 mm/km2 and 0.001 mm/km2 respectively. The 29 year average monthly and yearly surface runoff yield of Agarfa Small Scale Irrigation project sub-basin was 0.53 and 6.36 mm respectively. The estimated surface runoff yield have crucial value for providing information to identify the best and sustainable water resource development options. Therefore, the output of this study was used as an input to plan and implement effective water resources development project in and around the study area.