ASSESSING THE IMPACTS OF LAND USE/LAND COVER CHANGE ON HYDROLOGICAL PROCESSES OF BILATE WATERSHED, RIFT VALLEY BASIN, ETHIOPIA

Abstract

Land use land cover change is one of the responsible factor for changing the hydrological processes of watershed by altering the magnitude of surface runoff, interflow, baseflow, total simulation flow and evapotranspiration. Thus, effective information regarding the environm- ental response of land use land cover change is important to hydrologist, land use planners, watershed management and decision makers for sustainable water resource projects and ecosystem services. Consequently, this study was aimed at assessing the impacts of land use land cover change on hydrological processes of Bilate watershed between 1989, 2002 and 2015.Water balance simulation model (WaSiM) was used to access the impacts of land use land cover change on hydrological processes using landuse/land cover, soil, DEM, meteorological data and hydrological data as model inputs and the model run for three landuse/land cover satalite data to analyze the impacts of land use/land cover change on hydrological processes and water balance of Bilate watershed. The model was calibrated and validated using the streamflow of Bilate Tena station. The model was calibrated using streamflow data from 1989 to 2003 and validated from 2007 to 2015.The coefficient of efficiency (R2) and Nash Sutcliffe model efficiency (NSE) values were used to examine model performance and the result indicates 0.85 and 0.89 to coefficient of efficiency (R2) and 0.85 and 0.89 to Nash Sutcliffe model Efficiency (NSE) during calibration and validation respectively. Hence, the result indicates that the model performed well. The result of land use dynamics showed, land use land cover change have significant impact on runoff production, baseflow, interflow, evapotranspiration, total simulation flow and water balance of watershed. In the study watershed the change in total simulated flow increased 77.83% and surface runoff, interflow, and baseflow increased in 80.23%, 75.69% and 87.79% respectively and evapotranspiration decreased in 6% throughout study period (1989 to 2015). The results obtained from this study, addressed that the watershed exists under the land use land cover change impacts on hydrological processes and water balance. Therefore, the decision makers, planners and other stakeholders should design strategies to ensure the sustainability of the watershed hydrology for the sake of protecting every development activities for instance agricultural and other related activities within the watershed area.