Sediment transport is a worldwide environmental problem that degrades soil productivity, waterrnquality, causes sedimentation to the reservoirs and increases the probability of floods. Gefersarnreservoir, one of the surface water supply sources of Addis Ababa city for the last 70 years, facernthis problem. The reservoir supplies an average of 30,000m3 of treated water per day to the city.rnBased on the 1979 and 1998 bathymetric surveys, with the assumption of linear yearly siltation raternthere is 22,252 m3/year of sediment inflow to the reservoir. In terms of soil loss from the catchmentrnarea, this constitutes a loss of 575 tons/km2/year contributed by the catchment area. In this study,rnSoil and Water Assessment Tool (SWAT) was used to calibrate and validate a hydrologicrncomponent and sediment yield of Gefersa watershed. Back-calculation process was carried out tornestimate the natural inflow to the Gefersa reservoir. Sensitivity analysis, model calibration andrnvalidation were also performed to assess the model performance. Nine highly sensitive parametersrnwere identified of which curve number (CN2) was the most sensitive one. The coefficient ofrndetermination (Rrn2rn), Nash-Sutcliffe (ErnNSrn) and the percent difference for a quantity (D) was used tornevaluate model performance during calibration and validation. Results found were satisfactory andrnplausible for ungauged station i.e. Rrn2rn= 0.78. ErnNSrn= 0.77 and D=-15.3 for calibration and Rrn2rn= 0.72,rnErnNSrn= 0.70 and D=-20.7 for validation period. Sediment were calibrated and validated on annualrnbasis using D i.e.-1.37 for calibration and -6.9 for validation. Four scenarios are developed tornobserve the impact of land use changes. Based on this, change of 53% and 16% forest to agriculturernresulted in 74.5% and 52.89% increase in sediment load. And change of 35% and 18% rangeland tornagriculture land increase 40.47% and 29.51% increase in sediment load .Based on results ofrnmodeling, sediment reduction methods in the catchment as well as recovering storage capacity arernproposed. Of the available reservoir sediment management approach, watershed management is thernbest method to reduce the yield of sediment and its entry into the reservoir. Periodic sluicing ofrnsediments through operation of bottom outlet gates would also help to ease the problem.rnKey words: - Gefersa, Sediment, SWAT Watershed, Bathymetric survey