The Awash Basin is the most utilized and most developed basin in Ethiopia. After thernconstruction of the Koka dam the feature of the basin is changed in large extent. Heavyrnrainfall in the upstream catchments causes large inflow discharges to Koka Lake. Atrntimes where the water level is already close to the maximum water level, the excessrnwater must be discharged through the spillways in order to prevent overtopping of therndam. The discharge through the spillway, together with the water discharged throughrnthe power plant turbines, has in the past caused flooding in the downstream areas, mostrnnotably in August 1996. To prevent the downstream areas from flooding, the waterrnlevel in the lake could be lowered in advance provided the inflows could be forecasted.rnFor this reason, the FEWS-SFM was calibrated for the Upper Awash Basin using fivernyears (1991-1995) of stream flow and rainfall records. The model was verified usingrnanother five years data (1996-2000). Ground observed data were used for therncalibration for both the physical characteristics of the basin and the dynamic inputs:rnrainfall and potential evapotranspiration.rnSimulation was done in three scenarios of defining the basin. First the basin is definedrnto have a single outlet at Melka Hombole hydrologic station. The second scenariorndivided the basin into six subbasins and the last scenario is made by dividing therncatchment to thirty five subbasins. It is seen that the second scenario represented thernrainfall runoff to an acceptable range both visually and statistically. The Nash andrnSutcliff goodness of criteria (R2) was used for testing the model performance. R2 =rn0.63 was obtained for the calibration and the verification yield R2 = 0.6.rnThe simulation of the basin has underestimated the peak summer (July â€“ August) andrnoverestimated flow from March to June. The dry period flow is underestimated.rnHowever, further refinement of the DEM and investigation on the DEM andrninvestigation on the way soil properties influencing the rainfall runoff process in thernmodel may improve the model main rainy period flow and overestimation of the smallrnrainfall period. From the results obtained further investigation on the way soilrnproperties influencing the rainfall runoff process in the model is necessary.rnKey words: Awash, calibration, DEM, FEWS-SFM, flood, Koka, rainfall runoff,rnsimulation, verification.