Estimation of Catchment Sediment Yield using SWAT Model (Case Study Gidabo Dam, Rift Valley Basin, Ethiopia)
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Date
2019-04
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Addis Ababa University
Abstract
Poor land use practices and improper management systems have played a significant role in causing high soil erosion rates, sediment transport and loss of agricultural nutrients in Gidabo sub basin. This serious problem can also play great role on the silting up of reservoirs and shortening their age for reservoirs found around the basin. The purpose of this study was to estimate sediment yield of Gidabo watershed to reservoir and recommend appropriate reduction measures. The soil and water assessment tool (SWAT) model was applied to simulate the sediment yield from the Gidabo watershed (area 2634 sq. Kilometer) located in Borena zone of Oromia region and Sidama zone of SNNPRS, Ethiopia. Model calibration and validation process was conducted by using multi gauge calibration approach in monthly base using SWAT-CUP. The time series data from 1997 to 2002 was used for model calibration and the time series data from 2003 to 2006 were used to validate the model using the input parameter set for both gauging stations Aposto, Bedassa and Maesso. Time series plots and the statistical measures of coefficient of determination and Nash-Sutcliffe efficiency were used to evaluate the performance of the model. Flow calibration at dam outlet (Maesso station) gives coefficient of determination (R2) and Nash-Sutcliffe simulation efficiency (ENS) 0.80 and 0.65 respectively. Flow validation gives 0.85 and 0.81 for R2 and ENS values respectively. Sediment calibration gives R2 and ENS 0.79 and 0.67 respectively and validation test gives R2 and ENS 0.79 and 0.78 respectively. The two other stations, Aposto and Bedassa also shows good result of calibration and validation for both flow and sediment. This result indicates that the observed values show good agreement with simulated value for both flow and sediment yield. In this study, the SWAT model simulates average annual sediment yield of 95.32 ton/km2/year at dam outlet (Maesso station). Sub basin 4, 11,3,40 and 8 ranks first to fifth according to their Sediment yield respectively and found as erosion prone areas. For proper management of the watershed, from the scenarios developed, changing 30% of agricultural land to forest mixed reduces 27.2% of sediment volume and taken as best management method. Moreover, applying terracing and filter strip in low slope areas reduces 4.7% and 13% of sediment volume respectively and could give potential effect of best management practice.
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Keywords
Arc SWAT, SWAT CUP, sediment Yield, Gidabo Watershed