Abstract:
Dam failures can result in human death and financial loss. To establish hazard management measures, it is critical to map flood inundation for possible dam breach. Gereb Giba embankment dam is one of Ethiopia's most recent ongoing dams. The major purpose of this research is to assess the breach of the Gereb Giba embankment dam as well as map and identify flood hazards. The absence of a high-resolution DEM was the study's major problem. The data gap was filled with field-measured elevation data. To increase the DEM's accuracy in representing the river terrain model, the field data was integrated with the digital elevation model (DEM) (ALASKA 12.5m DEM). From the probable maximum precipitation calculated using the Hirschfield 1965 statistical approach, the HEC-HMS model was used to generate the probable maximum flood. The reservoir's peak outflow during the probable maximum flood is 3348.7 m3/s, according to the HEC-HMS model. This peak outflow raised the reservoir elevation to 1820m a.m.s.l., which is 0.3m higher than the dam crest level, indicating an over topping failure mode. To simulate over topping and piping mode failures, the HEC-RAS combined 1D/2D hydrodynamic model had been used. All essential geometry data was digitized using HEC-GeoRAS 10.3, and breach parameters were estimated using Froehlich's (2008) empirical equation from. For over topping and piping modes of failure, peak floods at the dam axis are 80801.27 m3/s and 55173.82 m3/s, respectively. The entire area flooded by an over topping breach event is 103.931 km2, whereas a piping breach event inundates 62.476 km2. The inundated area has a population of 4,269 people and 104,210 animals, respectively. If the dam falls, some privately owned cropland, forestland, and grasslands will be flooded. The dam's flood hazard classification was determined by combining the effects of flood depth and velocity. Gereb Gina embankment dam is classified as a high hazard dam since this result of flood depth times velocity over a broad floodplain is greater than 0.5 m2/s (high to extremely high hazard flood). As a result, interested institutions should devise hazard management methods to ensure public safety and protect economic interests in the flooded area
