Flood is probably the greatest devastating, wide spread and frequently natural hazard ofrnthe world wide that producing several socioeconomic and environmental consequencesrnwithin the affected floodplain. In Ethiopia, Awash River basin is one of the areasrnaffecting by flood plain problem and among Awash River basin, wonji to awashrnmelkessa is one the most frequently severed area by floodplain along Awash River, forrnthose flood risk analysis is so important.rnThe main objective of this study was flood inundation mapping and quantifies the risk ofrnflood on the area by using hydrological model HEC-HMS for peak flood forecasting forrndifferent return period and GIS extension HEC-GeoRAS integration with hydraulicrnmodel HEC-RAS for flood inundation mapping. For hydrological model (HEC-HMS)rndaily rainfall and stream flow data of 16 years from (1998-2013 G.C) was used. Among therndata used eight years for calibration and five years for validation of HEC-HMS model atrnwonji Gauged station. HEC-RAS model was calibrated and validated using satelliternimaginary Landsat-7 flood event and observed flood event of September, 06/2000 andrnSeptember, 22/2007 G.C respectively. The missing values were filled by using normalrnration method for daily precipitation data. Consistent data was checked by double massrncurve method. The initial and constant loss method was selected for loss method and forrntransform method Clark unit hydrography was applied.rnThe estimated peak flood by hydrological model (HEC-HMS) was 147.2m3/s, 161.9m3/s,rn329.4m3/s, 409.5m3/s and 506.8m3/s for 5year, 10year, 25years, 50years and 100yearrnreturn period correspondingly. The flood inundated area corresponding to peak floodrnwere 1052.7 hectare, 1086.9 hectare, 1429.5 hectare, 1559.1 hectare and 1694.1 hectarernrespectively. The total crop losses were calculated for flood inundated area, for 5 yearsrnand 100 year return period of crop loss were 75501.6 quintal and 121503 quintalrncorrespondingly.rnThus finding of the study may help in planning and management of flood plain area tornmitigate probable disaster through technical approach.