Runoff And Sediment Yield Simulation In The Weyib Watershed Genale-dawa Basin Ethiopia

The SWAT model was applied to simulate the runoff and sediment yield from the Weyibrnwatershed. This watershed has an area of 24369.6 km2rnand located in South-Eastern part ofrnEthiopia, sharing two regional states, Oromia and Somali. The objective of this study was tornestimate soil loss rate in the study watershed and to identify appropriate intervention measures torncontrol erosion. In spite of the serious erosion problems in the study watershed, so far only fewrnstudies related to erosion are available. Consequently, this study was conducted with the aim ofrncontributing to the exiting insufficient quantitative information on soil erosion problems. Due tornthe absence of measurements for some of the stations, about 25 years meteorological data and 21rnyears flow and sediment data generated by regional equations were used for the analysis. On thernother hand, the SUFI2 program in the SWAT-CUP was applied for model calibration andrnvalidation using time series data from 1992-2012. The model prediction efficiency was evaluatedrnusing statistical model performance indicators like, coefficient of determination (R2rn) and NashSutcliffe model Efficiency (ENS) and the result showed that both surface runoff and sedimentrnyield were estimated satisfactorily, with an Rrn2rnand NSE values of greater than 0.67 each, both forrncalibration (1994–2004) and validation (2005-2012) periods. The model prediction for the averagernannual precipitation and run-off was 1029.2mm and 311.30mm, respectively; whereas, the modelrnprediction for the average annual total sediment load was 1.23t/ha. The annual soil loss estimatedrnby the model for the Weyib watershed during the simulation period 1992-2012 ranges from 12.49rnha−1rnyear−1rnto 88.36 ha−1rnyear−1rn, with an average value of 37.33 tons ha−1rnyear−1rn. In this study, Subwatershed 6, 7, 8, 10 and 12 were found to have the maximum annual sediment load, having anrnannual sediment load of greater than 20 tons/ha/yr, sub-watershed 8 being the most erodible area,rnand as these sub-watersheds were most sensitive to erosion, they were labeled as erosion hotspotrnareas. Different intervention scenarios were developed for erosion control and proper managementrnof the watershed. Simulation results for these scenarios reflected that, 35-78% sediment yieldrnreduction could be achieved by implementing filter strips, stone bunds, contour farming, fanyarnjuu, bench terraces and from the combination of these. On the other hand, conversion ofrnagricultural lands to forest areas reflected a 10-45% sediment yield reduction.

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