Thesis Open Access
ALMAZ GIRMA MAMMOO; Dr. Brook Abate (PhD)
The potential effects of land use/cover change resulting soil erosion and producing over sediment on surface water source of reservoirs, which are losing their capacity due to sedimentation processes, and are therefore seriously threatened on their performance. Therefore the main objective of this study is to evaluate the impact of land use land cover change on reservoir sedimentation in Didessa watershed. To show the impact of land use land cover change on total sediment loading the three independent models were runs simulations for the same period from 1990 to 2010. The performance of the SWAT model was evaluated through sensitivity analysis, calibration, and validation using SWAT-CUP software SUFI 2 programs. The model calibrated for three independent land use model using flow data from year 1990 to 2003 for calibration and from year 2004 to 2010 for validated respectively. The stream flow calibration and validation results showed good match between measured and simulated data with acceptable range, coefficient of determination, R2 ( 0.74 to 0.76 for Calibration and 0.76 to 0.82 for Validation) and Nash-Sutcliffe efficiency, NS (0.67 to 0.72 for Calibration and 0.72 to 0.79 for Validation).The sediment calibration and validation results showed good match between measured and simulated data with acceptable range, coefficient of determination, R2 ( 0.69 to 0.70 for Calibration and 0.77 to 0.80 for Validation) and Nash-Sutcliffe efficiency, NS (0.62 to 0.67 for Calibration and 0.74 to 0.78 for Validation). The actual sediment yield result for the watershed value ranges from 0.26 ton/ha/yr to 25.84 ton/ha/yr for 1990 land use, from 1.47 ton/ha/yr to 29.16 ton/ha/yr for 2003 land use and from 0.71 ton/ha/yr to 38.17 ton/ha/yr for 2013 land use land cover type. The mean annual total sediment loading was 6.98ton/ha/yr (697.67ton/km2/yr), 8.41ton/ha/year (841.43ton/km2/yr) and 9.01t/ha/yr (901.38ton/km2/yr) for 1990, 2003 and 2013 land uses land cover respectively. The result of the study were used to Proper land use practices and watershed management should be applied by stakeholders in order to make the sub basins more productive and reduce the adverse impacts on the down streams due to soil erosion and sediment problems. Integrating land use change models with hydrologic models could be applied to predict the impacts of land use land cover changes on the stream flow and sediment yield, in the watershed.