SWAT based Evaluation of the effect of Land use change on Reservoir Sedimentation (Case Study of Gomit Reservoir Watershed, Estie Woreda, Amhara, Ethiopia)

Abstract

The soil and water assessment tool (SWAT) is examined for the prediction of sediment yield in Gomit River watershed. Poor land use practices and improper management systems have played a significant role in aggravating high soil erosion rates, sediment transport and loss of agricultural nutrients. Sedimentation reduces water storage capacity and negatively affects water supply, flood control capability, river barge navigation, viability of aquatic life, and the recreational value of reservoirs. Public funds for best management practices (BMPs) to reduce sedimentation are increasingly limited, and federal, state, and local governments are placing more emphasis on achieving economically efficient sediment reduction. Erosion of cropland is a major source of sediment accumulation in reservoirs. The main objective of this study is to evaluate the effect of land use change on reservoir sedimentation and to predict sediment yields in study area. A physically based watershed model was applied based on its necessity to Gomit River watershed for modeling of the hydrology and sediment yield. The model is calibrated and validated for both flow and sediment concentration at Gomit dam reservoir outlet (223.81km2) to estimate the sediment .The calibrated model can be used for further analysis of the effect of land use change on reservoir sedimentation as well as other different management scenarios on stream flows and soil erosion. The area of watershed is subdivided in to 3 sub basins by using soil water assessment tool (SWAT) model. SWAT_CUP is used to calibrate the model parameters of flow and sediment with the time series of 2000 to 2009 for calibration and 2010 to 2014 for validation. The Calibrated and validated values of stream flow and sediment yields are, (R2=0.80, ENS=0.80 PBIAS=24.5, RSR=0.45) and (R2=0.86, ENS=0.84, PBIAS=17.4 and RSR=0.40) for flow. Similarly (R2=80, ENS=78, PBIAS=20.5RSR=0.46) and (R2=94, ENS=84, PBIAS=34.6, RSR=0.42) respectively for sediment yields. For this study two watershed management intervention measures are used ;(i) land use redesign for steep slopes greater than30% in the watershed of Gomit (ii) Implementation of Terracing activities in agricultural lands of the watershed. By applying both land use redesign for steep slopes and terracing activities the sediment yields of Gomit watershed reduced by7.64% and18.03% respectively.