HYDROLOGICAL IMPACTS DUE TO LAND-USE AND LAND-COVER CHANGES OF KETAR WATERSHED, LAKE ZIWAY CATCHMENT, ETHIOPIA

Human health and welfare, food security and industrial developments are dependent on adequate supplies of suitable water; however, water resources are finite in space and time and affected by many parameters. One of the parameters that affect the volume of water flowing in a watershed is land-use and land-cover of the watershed area. Having investigated the influence of human induced abstractions and its impact on the hydrology of the basin, it is also important to investigate of land-use/land-cover changes within the basin and their impacts on the hydrological regime. Based on this the main objectives of this study is to assess the temporal impacts of land-use and land-cover changes on stream flow of Ketar river which is located at south east central part of Ethiopia. The study also evaluated land-use and land-cover changes between 1986 and 2010 years and its impact on watershed hydrology. Classifications of historical land-use and land-cover changes occurred in the watershed were performed using 1986 and 2010 years satellite images with the help of ERDAS and GIS software. To investigate the impacts of land-use and land-cover change on stream flow, Semi-distributed hydrological model, Soil and Water Assessment Tool (SWAT) was applied. Following to model sensitivity analysis, calibration and validation was performed using historical recorded river flow data. The analysis result of land-use and land-cover change show that, an outspread of agricultural land and settlement and reduction of forest land and grass land in the study area. The evaluation of the SWAT model response to the land-use/land-cover change indicate that, the mean wet monthly flow for 2010 land cover increased by 3.8% compared to the 1986 land cover. On the other hand, average monthly flow in dry season is decreased by 12.3% in 2010 compared to 1986 land-cover. It is concluded that because of increasing number of population in alarming rates, it is expected that, the existing marginal lands at present will changed to agricultural lands which can affect health of hydrological process within the watershed and thereby threatens the livelihoods of the inhabitants.