Hydraulic Modeling and Flood Mapping of Flood Plain Along Megech River, Upper Blue Nile Basin, Ethiopia

Every year, devastating floods occur in numerous places around the world. Floods are also a daily occurrence in Ethiopia, wreaking havoc and claiming lives, especially in low lying areas such as cities. The Dembia floodplain is one of the most flood-prone districts in Ethiopia. Most victims of flood disasters are people who live in rural areas and make their living from agriculture and livestock near a floodplain. Due to the flooding on the Megech River in Ethiopia, the focus of the study was on hydraulic modeling and flood mapping. Combining the technologies HEC-HMS, HEC-GeoHMS, HEC-RAS and ArcGIS to create a regional model for floodplain identification and representation resulted in floodplain mapping. Using daily time series data, the hydrologic model HEC-HMS was calibrated for return periods of 2, 10, 25, 50, and 100 years. The model HEC-HMS provides 139.7 m<sup>3</sup>s<sup>-1</sup>, 228.2 m<sup>3</sup>s<sup>-1</sup>, 369.7 m<sup>3</sup>s<sup>-1</sup>, 437.8 m<sup>3</sup>s<sup>-1</sup>, and 568.8 m<sup>3</sup>s<sup>-1</sup> for return periods of 2, 10, 25, 50, and 100, respectively. A one-dimensional hydraulic model, HEC-RAS, with the HEC-GeoRAS tool extension in ArcGIS was used for flood mapping. The inundation mapping results in 19.92 km<sup>2</sup>, 23.76 km<sup>2</sup>, 25.32 km<sup>2</sup>, 28.65 km<sup>2</sup>, and 30.09 km<sup>2</sup> of inundation area for return periods of 2, 10, 25, 50, and 100, respectively. According to the study, floods have significant impacts as they inundate agricultural and pastoral lands, which has a direct negative impact on of the society. Moreover, flood hazards were evaluated based on the return period and water depth. Therefore, central and local governments should introduce appropriate policies and measures to address this problem.