Dam Breach Flood Prediction and Mapping: A Case Study of Gomit Small Dam, Amhara Region

The Gomit Earth Dam, constructed for irrigation, is currently in a critical state due to structural damage and exposure of the clay core, posing a significant risk of catastrophic failure. This study simulates the potential breach flood under probable maximum flood (PMF) conditions and delineates flood inundation extents to assess impacts on downstream areas and inform mitigation strategies. The research employs five key software tools: Global Mapper, ArcGIS, HEC-RAS, HEC-GeoRAS, and RAS Mapper to model dam breach hydraulics and map flood inundation. Field-surveyed topographic data with 20-m interval cross-sections were used to create accurate terrain representations. Simulations were conducted for two scenarios: sunny day failure and PMF failure, with detailed flood hazard analysis focusing on the PMF scenario. Results indicate a peak breach outflow of 1914.26 m<sup>3</sup>/s, 1.28 times greater than sunny day failure and 18.65 times the PMF inflow, with flood depths ranging from 7.06 m near the dam to 0.72–1.58 m across overbanks downstream. Flow velocities reached up to 12.32 m/s, and the flood wave arrival time varied from 0.077 to 0.386 hours after breach initiation. The inundated area totals approximately 38.92 hectares, representing 32.44% of the irrigated command area, with significant implications for agriculture, infrastructure, and community safety. Approximately 26 households, totaling over 100 people, are at high risk of life-threatening impacts, food insecurity, and property damage. This study underscores the urgent need for structural maintenance, early warning systems, and community-based flood risk management. Limitations include a lack of observed flood data for model calibration and consideration of a single flood scenario. Future research should incorporate multiple breach scenarios, long-term monitoring, and the impacts of climate variability to enhance the preparedness and resilience of irrigation infrastructure.