Impacts of Land Use Land Cover Change on Streamflow and Sediment Yield on Awata Watershed, Genale Dawa River Basin, Ethiopia

Abstract

Changes in LULC are major variable that impacts many parts of the global environment which causing soil erosion and sediment transport that affecting different watersheds. This study was designed for the assessment of impacts of LULCC on streamflow and sediment yield in the Awata watershed by using SWAT model. Spatial data and weather data were major inputs for the model. The LULC classification for two different years of 2002 and 2020 were done by using ERDAS Imagine 2015.Based on the result, the significant change were occurred in the study period seen between the 2002 and 2020 Agriculture and Shrubland increased by 11.06% and 11.43% respectively. Forest, Water bodies and Grassland decreased by 11.97%,3.643%, and 8.21% in the most part of the watershed. The model simulation was done by dividing the total area watershed of 1920.3Km2 into 29 sub basins and 229 Hydrologic Response Units (HRUs) for the period (1988-2018). The model calibration and validation was carried out using Sequential Uncertainty Fitting (SUFI-2) algorithm in SWAT-Calibration Uncertainty Programs (SWAT- CUP) on monthly basis. The model was calibrated for the period of (1988-2005) including the first two years as warm-up period and validated for (2006-2013) for both stream flow and sediment yield by using more sensitive parameters. The model performance was evaluated by coefficient of determination (R2 ), Nash Sutcliff Efficiency (NSE), and Percent bias (PBIAS) to be quit acceptable for both stream flow and sediment yield estimation in the watershed. It has resulted in (R2=0.62, NSE=0.65, and PBIAS= 8.2%) for calibration and (R2=0.66, NSE=0.67, and PBIAS=6.1%) for validation of stream flow. Whereas (R2=0.58, NSE=0.72, and PBIAS=11.5%) for calibration and (R2=0.68, NSE=0.61, and PBIAS=9.4%) for validation of sediment yield. The result shows that the wet monthly flow increased from 19.49 m3 /s in 2002 to 20.65 m 3 /s in 2020 by 1.6 m3 /s and the dry monthly flow decreased from 1.32m 3 /s in 2002 to 1.16m 3 /s in 2020 by 0.16m3 /s during the study period (2002- 2020). Whereas the change from 2002 to 2020 in sediment yield occurred within increased value from 12.6ton/ha/yr to 14.4 ton/ha/yr by 1.8 ton/ha/yr in wet season and decreased for dry season from 0.8 ton/ha/yr to 0.657 ton/ha/yr by 0.1425 ton/ha/yr. Generally, the study result indicated flow and sediment yield during wet season increased for both and whereas during dry season flow decreased and also decreased in sediment yield accordingly