Simulation of urban environment flood inundation from potential dam break: case of Midimar Embankment Dam, Tigray, Northern Ethiopia

Urban settlements and infrastructures have been developed along rivers, often are located downstream of water storage structures such as dams or lakes. However, such proximity exposes many lives and properties to flood hazards. Hence, prediction of floods generated by the potential collapse of dams and their consequences on downstream urban areas helps to devise an appropriate early warning system and emergency action. This study simulates flood inundation effects of Midimar dam break on the downstream areas of Adwa town, located in Tigray regional state, northern Ethiopia. For this purpose, the study incorporated both Hydrologic Engineering Center Hydrological Modeling System (HEC-HMS) and hydraulic simulation with Hydrologic Engineering Center River Analysis System (HEC-RAS) for Midimar dam break analysis. The results from this study showed that both overtopping and piping failure scenarios at 423 m3/s probable maximum flood condition of Midimar reservoir represents a significant threat to downstream areas in an event of dam break. Accordingly, there is a significant risk on 16,168 human lives and 3319 houses. A loss of physical properties are expected to occur especially in the Adi-Abun and Adwa areas situated along the river floodplain area of 6.4 km2. It is also evident from the study that major infrastructure including seven out of nine bridges along the downstream river will be overflown. Hence, provision of flood hazard prevention strategy, emergency plan; and adequate buffer zone between the flood prone area and residential settlement and urban development sites need to be enforced. This study helps decision-making authorities in land use planning and developing emergency action plans to mitigate catastrophic loss of human life and property.