SWAT Based Evaluation of the Effect of Land Use/Land Cover Change on Reservoir Inflow and Sediment Yield (Case Study on Gidabo Reservoir Watershed, Ethiopia)

Abstract

Water resource project planning and implementation are affected by many parameters. Among those parameters land use and land cover change has been one of a factor that alter the hydrologic response of the watersheds leading to influencing stream flow and sediment yield changes. The purpose of this study was to evaluate the impact of the land cover changes on stream inflow and sediment yield to the reservoir in Gidabo watershed, Ethiopia using Soil and Water Assessment Tool (SWAT). Land use map of 1986, 1994 and 2008 were used for analysis. The simulation was done by dividing the watershed into 43 sub watershed and by assigning a hydrological response unit based on multiple HRU definition. The model calibration for stream flow and sediment was carried out using time serial data from 01 January 1995 to 31 December 2000 and a validation period from 01 January 2001 to 31 December 2003. The result of land use and land cover analysis has showed that the cultivated land has mostly expanded, while forest, grassland and shrub lands were decreased during the study period of 1986 - 2008. The result of sensitivity analysis showed that the stream flow is highly sensitive to soil evaporation compensation factor (Esco) and sediment is most sensitive to USLE support practice factor (Usle_P). The calibration results for both stream flow and sediment yield showed good match between measured and simulated data with the coefficient of determination of 0.86 and 0.83, Nash Sutcliffe efficiency of 0.85 and 0.77 and percentage bias of -3.94% and -4.30% respectively. And the result for validation for both stream flow and sediment showed good result with Coefficient of determination of 0.83 and 0.82, Nash-Sutcliffe efficiency of 0.81 and 0.79 and percentage bias of 3.15 and 0.57%. The evaluation of the model indicates that mean annual stream inflow was increased by 20.14% between 1986 to 2008 LULC. Similarly mean annual sediment yield was increased by 6.78t/ha between 1986 to 2008 LULC.