Impact Of Land Use And Land Cover Change On Sediment Yield Using Swat Model In Birr Watershed , Blue Nile Basin, Ethiopia

Abstract

Birr watershed is found 60 km south-west of Bahirdar at the non-asphalted road connecting Bahirdar to FersBet town, Degadamot woreda. The effects of land use and land cover change have an impact on sediment yield on the Birr watershed. The study mainly focuses on impact of land use and cover change on sediment yield and stream flow under different land use and land cover change of the sub basin. Other effects on the sub basin, like water balance, ground water changes, and climate change impact would not be covered in the study. Three hypothetically land use land cover change scenarios were developed. A physically based, spatially distributed hydrological model, SWAT would be used to simulate LULC effects in the hydrological response (sediment and stream flow) of Birr sub basin. Intensively cultivation land use increased in the watershed whereas moderately cultivation land use decreased. The performance of the SWAT model was evaluated through sensitivity analysis, calibration and validation. Both the calibration and validation result shows good agreement between observed and simulated stream flow R 2=0.83, NSE=0.79 and R2 =0.76, NSE=0.74 respectively and sediment yield R 2=0.77, NSE= 0.73 and R2=0.72, NSE=0.07 respectively. The model was capable of simulating stream flow and sediment yield for Birr watershed. But the result from sediment simulation was not good performance in the validation period. This is inability of SWAT model simulate gully erosion and land slide. Sensitivity analysis using SWAT model has pointed out that some crucial parameters control the stream flow and sediment yield in the catchment. Soil erosion is not solely driven by rill and sheet erosion. Sever sediment yield and stream flow was observed on dominantly cultivated areas in the watershed. The results could have been improved by using longer period of sediment recorded and better quality land use and soil data.