The Impact of Land Use Change on the Hydrology of the Angereb Watershed, Ethiopia

Land use/land cover change has been responsible for altering the hydrologic response of watersheds leading to impacting river flows. Various water resources projects’’ planning and implementation will require knowledge of the extent of these changes on watershed hydrology. The main objective of this study is to assess the impact of the land use changes on the flow of the Angereb watershed which is located in the upper Tana basin, Ethiopia. In particular, the study analyses the land cover change between the 1985 and 2011, and the effect these changes have had on the runoff and reservoir inflows in the watershed. The land cover changes within the watershed were examined through classification of satellite images with integrated the use of image and spatial analysis. The Soil and Water Assessment Tool (SWAT) model was used to investigate the impact of land cover change on stream flow. The model was calibrated and validated using historical flow data. Land cover change analysis has shown that cultivated land and built up areas have increased, while the forest and grass land has decreased between 1985 and 2011. Sensitivity analysis has shown that the curve number is the most sensitive parameter that affects the hydrology of the watershed. The model was calibrated for the year using flow data from 1992 to 2000 and validated from 2001 to 2004. The R2 and Nash Sutcliffe Efficiency (NSE) values for the watershed were 0.85 and 0.76 for calibration, and 0.79 and 0.72 for validation, respectively. The evaluation of the SWAT model response to the land cover has shown that the mean wet monthly flow for 2011 land cover increased by 39% compared to the 1985 land cover. On the other hand, dry average monthly flow decreased by 46% in 2011 compared to 1985 land cover.