Dam Break Analysis and Flood Inundation Mapping of Polavaram Dam Using HEC-RAS

Abstract

Failure of a dam can release a large volume of stored water suddenly and endanger the population and property downstream. This study presents a two-dimensional dam break analysis and flood inundation mapping of the Polavaram Dam, a multipurpose project on the Godavari River in Eluru District, Andhra Pradesh, India, using HEC-RAS 6.6. The reservoir was represented by a storage area and the downstream floodplain by a 2-D flow area with a 50 m mesh, built on SRTM 30 m terrain data and Esri 10 m land use/land cover data. Breach of the earth-cum-rock-fill (ECRF) dam section was simulated for overtopping and piping failure using five empirical breach methods, namely Froehlich (2008), Froehlich (1995), Von Thun and Gillette, Xu and Zhang, and MacDonald et al., for a simulation period of 24 hours. The Froehlich (2008) overtopping scenario gave the highest peak breach discharge of 174,862 m³/s and the largest inundation area of 717.224 km²; the corresponding piping scenario gave 120,453 m³/s and 559.097 km². Across the ten scenarios the inundation area ranged from 172.863 km² to 717.224 km². Maximum flood depth, velocity and water surface elevation were extracted at three downstream locations, where the maximum depth reached 17.138 m at Area 1. The results show that the choice of breach method strongly affects the peak discharge and flood extent, and the maps and values obtained can support emergency action planning and flood-hazard assessment downstream of the dam.