Evaluating the impact of land use and land cover changes on sediment yield dynamics in the upper Awash basin, Ethiopia the case of Koka reservoir.

ABSTRACT

Land Use and Land Cover changes (LULC) are the driving forces to change the hydrological response of the watershed. In this study, the Quantum Geography Information System Interference Soil and Water Assessment Tool Plus (QSWAT-PLUS) model was applied to evaluate the effects of LULC on sediment load at the Upper Awash River Basin (UARB) which are causing sedimentation problems in Koka reservoir. The LULC data for 2005, 2010, and 2015 were obtained from historical satellite images using Earth Resources Observation and Science (ERDAS) 2014. The classification of LULC changes showed that the agricultural practice, and the settlement land both increased by 6.7 % and 6.3 %, respectively. In contrast, the forest area, woodland, shrubland, and water bodies decreased by 5.47 %,0.93 %,0.96 %, and 1.34 % from 2000 to 2015 respectively. The model evaluation results were satisfactory for the three LULC scenarios. The average annual surface runoff volume for the 2005 LULC data was 182.2 mm, which increased to 193.29 mm in 2010 and 205.3 mm in 2015. Similarly, the average annual sediment yield that would enter to the Koka reservoir under the 2005, 2010, and 2015 LULC scenarios were 26.03 t/ha/yr, 26.34 t/ha/yr, and 28.33 t/ha/yr respectively. In general, streamflow, surface runoff, and sediment output increased by 4.55 %, 12.68 %, and 8.84 %, respectively due to the rapid change of LULC from 2000 to 2015. Temporarily, the sediment load at the upstream side of the Koka Dam watershed was 60.8 % during the wet season. The southwest direction of the watershed was identified as the primary erosion-prone area. Based on the simulation results, the filter strip, contour, and terraces reduced the watershed sediment yield by up to 60 %, 65 %, and 80 %, respectively. Therefore, the selected best management practices are highly effective in reducing silt along the entire upstream side of the Koka Dam watershed.