MODELING THE IMACT OF LAND USE/LANDCOVER DYNAMICS ON STREAM FLOW AND SEDIMENT YIELD: A CASE STUDY OF UPPER AWASH BASIN

The population growth, deforestation and urban area expansion for the last 30 years cause’s changes in land use/cover of Upper Awash basin. The effect of land use/cover changes have impacted the stream flow and sediment yield of the watershed. The knowledge of how land use/land cover change influence on watershed hydrology will enable local government and policy makers to formulate and implement effective and appropriate response strategies to minimize the undesirable effect of future land use/land cover change or modification. In this research SWAT model was used for analyzing the land use/cover changes on the hydrology of the watershed (stream flow and sediment yield) and its impact on reservoir sedimentation. Model calibration and validation was done at Hombole station. For 1990 and 2013 land use/cover change calibration and validation was 1990-2007 and 2008-2014 respectively. Result from both land use/cover show acceptable range, 0.72-0.89 for R2, 0.7-0.83 for NSE. The impact of land use/cover change was analyzed by using three criteria; the first was by selecting sub basin with the highest surface runoff and sediment yield. The second was by selecting the lowest surface runoff and sediment yield, and the last one was by selecting sub basin, which had different land use/cover using 1990 and 2013 land use/cover map. The model estimated stream flow and sediment yield from Upper Awash Basin for both 1990 and 2013 land use/cover maps. Therefore, 45.05 m3/s of stream flow and 57.06 Mtone annual sediment yield were entered to Koka dam during 1990 and 66.56 m3/s of stream flow and 47.36 Mtone annual sediment yield was extracted from the upper awash basin during 2013 land use/land cover data. During this period agricultural land was decreased by 28%, natural forest land decrease by 47.78%. In addition, urban area was increased by 166%, while plantation area appeared to be highly increased. The result obtained shows that there is 47.75 % increment of stream flow and 17 % decrement of sediment yield in 2013 as compared to 1990 land use/land cover data