Impact Of Land Use/Land Cover Change On Stream Flow And Sediment Yield Using Swat Model, A Case Of Melka Kunture Sub- Watershed In The Upper Awash River Basin, Ethiopia

Abstract

Stream Flow and Sediment yield estimations are needed for studies of reservoir sedimentation, river Morphology and soil and water conservation planning. An understanding of hydrological processes is essential for investigating impacts of land use and land cover changes on water resources. The objective of this study is to estimate stream flow and sediment yield of Melka Kunture sub watershed by using hydrologic model SWAT and the study result will provide an insight to planners and decision makers regarding the status of stream flow and sediment yield so that appropriate management measure will be undertaken. The area of Sub Watershed was discretized into 7 sub catchments using ArcSWAT interface of the model. The Sequential Uncertainty Fitting (SUFI2) calibration process built in SWAT calibration and uncertainty program (SWAT-CUP) were used to calibrate the model parameters using time series flow and sediment load data of 2001 to 2005 and validated with the observed data from years 2005 to 2008. The performance of the model was evaluated through Sensitivity Analysis, Calibration and Validation. The coefficient of determination (R2), Nash-Sutcliffe Efficiency (NSE) and Percent Bias ( 𝑃𝑏𝑖𝑎𝑠) values for the daily Stream Flow by using SUFI2 optimization technique was obtained as 0.85, 0.76 and -4.6 respectively for the calibration period and 0.76, 0.74 and 5.1 respectively for validation period. For monthly sediment yield R2, NSE and 𝑃𝑏𝑖𝑎𝑠 for calibration was computed as 0.72, 0.78 and -13.5 respectively, and 0.71, 0.69 and -14.1 respectively for validation period. Simulation of effect of land use land cover change on stream flow and sediment yield, evidently indicated that average monthly stream flow and sediment yields were increased due to the reduction of Forest land and Increment of Agricultural land. Stream flow was increased by 7.78% from 1986 to 2000 and 4.84% from 2000 to 2010.similarly Sediment Yield also increased by 58.62% from 1986 to 2000 and 4.34% from 2000 to 2010. Average annual sediment yield of Melka Kunture watershed was estimated as 21.17 t/ha/y, 33.58 t/ha/y and 35.04 t/ha/y using LULC map of 1986, 2000, and 2010 respectively, which exceeds the average sediment yield of the Upper Awash sub-Basin. Therefore, Stakeholders must provide appropriate mitigation measures to reduce the stream flow and sediment yield of Melka Kunture Sub Watershed.