Probabilistic Mapping And Sensitivity Assessment Of Dam Breach Flood Inundation

Abstract

Dam breach floods present severe threats to downstream populations, infrastructure, and ecosystems. This study conducts a probabilistic flood inundation mapping and sensitivity analysis for the Almatti Dam on the Krishna River, Karnataka, India. The latitude and longitude of the Almatti dam site are 16°19'00”N and 75°53’15’’ E respectively. The dam is a blend of earth-fill and masonry construction, stretching over 1,564.83 meters in length and height of 49.29 meters. It holds a substantial storage capacity of around 123 TMC and manages water from a vast catchment area of about 35,925 square kilometers. The project is jointly managed by two government agencies: Krishna Bhagya Jala Nigam Limited (KBJNL), responsible for water storage, reservoir operations, and irrigation management, and Karnataka Power Corporation Limited (KPCL), which operates the hydroelectric plant with an installed capacity of up to 290 MW.Using a Monte Carlo simulation framework integrated with HEC-RAS 2D hydrodynamic modeling, uncertainty in breach parameters (e.g., breach width, formation time) and hydrological inputs (e.g., inflow hydrographs, Manning’s roughness) is incorporated to generate probabilistic flood hazard maps. Exceedance probabilities of inundation extents, depths, and arrival times are derived from multiple simulated scenarios. Sensitivity analysis identifies breach size, formation time, and reservoir level as the most influential factors in downstream hazard magnitude. The results provide a robust basis for flood risk assessment, supporting Almatti dam authorities in designing effective emergency action plans, evacuation strategies, and early warning systems by explicitly accounting for uncertainty in dam-break events.