Runoff and sediment yield Estimation using Soil and Water Assessment Tool (SWAT) model in Fincha watershed, Western Ethiopia

Abstract

Runoff and sediment yields are the main problems that affect environment and dams by reducing the storage capacity of reservoirs and the life expectance of the dam. These effects were due lack of appropriate prediction of the problems and lack of best watershed management practices. The aim of this study was to estimate runoff volume, annual of sediment yield and to identify vulnerable area of Fincha watershed at sub basin level. The main input data used were weather data, spatial data and hydrological data and were collected from different sources. The main sources of these data were Ministry of Water, Irrigation and Electricity of Ethiopia, Ethiopian Mapping Agency, National Meteorological Agency, and International Water Management Institute. Soil and Water Assessment Tool (SWAT) version 2012, Geographic Information System (GIS) version 10.3 interfaces has been used to attain the aims of the study. Simulated model was resulted with 21 sub basins and 205 HRUs. For sensitivity analysis, calibration and validation of monthly stream flow, SUFI2 uncertainty program of SWAT CUP version 2012 has been used. Calibrated and validated monthly stream flow at the outlet of watershed were resulted with coefficient of determination R2 and Nash- Sutcliffe, ENS 0.81 and 0.78 and 0.76 and 0.74 respectively. The model was evaluated using coefficient of determination, R2 and Nash- Sutcliffe, ENS based on monthly stream flow data since the available data for sediment was limited. From R 2 and ENS results, the model has good capacity to estimate runoff volume since the values were satisfactory. The maximum and minimum annual surface runoffs at sub basin levels were 567.43 mm and 10 mm respectively. Average annual values of surface runoff from Fincha watershed was 242.7mm and average annual sediment yield was 25.7 ton/ha. Both surface runoff and sediment yield were discussed at sub basin level to identify the prone area of the catchment. From the spatial distributions, the values of sediment yield vary from 0.3 to 65 ton/ha/year depending properties of the sub basins and the prone areas were sub basins 1, 11 and 14 when compared with the rest of sub basins. The estimated values of runoff and sediment yields in Fincha watershed have significant impacts on the catchment, water bodies, communities and Fincha hydropower reservoir. Therefore, further detail investigation and appropriate watershed management practices should be applied.