Flood Hazard Mapping of Flood Inundation Area of Huluka River Catchment in Ethiopia

Abstract Floods are the most destructive of all-natural disasters in the globe, wreaking havoc on lives and property. Many locations in Ethiopia are experiencing flooding, and Ambo, like other tropical cities in Ethiopia, is experiencing a flash flood this can be minimized by giving attention to flood hazard measures. One of these measures is inundating flood hazard areas. Therefore, this study was conducted to map flood hazard maps along the Huluka River using GIS, HEC-HMS, and HEC-RAS in GIS environs. Flood Hazard mapping is used to define the zones which are more susceptible to flooding along the river when the release of a stream surpasses the bank-full stage along the river. The normal ratio approach was utilized to fill in missing values in precipitation data, and a double mass curve was used to ensure data consistency. Precipitation loss modeling, surplus precipitation translation to direct runoff, base flow modeling, and flood routing, the Soil Conservation Service-Curve Number, Soil Conservation Service-Unit Hydrograph, monthly constant, and Muskingum methods were used. Performance assessment approaches such as Nash Sutcliff Efficiency (NSE) and Coefficient of Determination were used to assess the model's performance (R2). During calibration and validation, Nash Sutcliff Efficiency was 0.77 and 0.7, respectively, while the coefficient of determination was 0.86 and 0.9, respectively. Flood frequency analysis was carried out utilizing the frequency storm method developed by HEC-HMS for 10, 25, 50, and 100-year return periods. For each return period, the peak flood was 38, 47, 55, and 61.5 m3/s, respectively. Using HEC-RAS and inundation areas of 98.9ha, 102ha, 104ha, and 106.4 ha, flood inundation mapping was modeled for a peak flood of each return period.