Dam Break Flood Inundation Mapping of Umrar Dam Using HEC-RAS: Fid-Bau Portal

Dam Break Flood Inundation Mapping of Umrar Dam Using HEC-RAS

Prasad, Bikram / Tiwari, H. L. / Gupta, Sunny

Flood inundation mapping can assist with municipal and urban growth planning, disaster management, flood insurance rates, and ecological studies. Both the ability to forecast the behavior of the stream in question for various recurrence interval storm events and the ability to interpret the forecasted results into a plan-view extent of flooding are required for mapping a flood plain. Dam break was modeled and analyzed using the HEC-RAS model based on the dam breach parameters. The Hydrologic Engineering Center River Analysis System (HEC-RAS) can simulate flood events and generate water surface profiles along the length of a stream model. Using the companion GIS tool, HEC-GeoRAS, those water surface profiles can be easily converted to flood inundation maps. The type of dam and the dam’s historical failures is used to select an overtopping failure mode. Different regression equations were used to estimate breach parameters, and the final breach parameters for the dam were chosen, which were derived by Froehlich. In this study, two different types of DEMs were used: first, an Advanced Land Observing Satellite (ALOS) The Phased Array Type L-band Synthetic Aperture Radar (PALSAR) DEM with a resolution of 12.5 m, and second, an Shuttle Radar Topography Mission (SRTM) DEM with a resolution of 30 m. Both DEMs were compared, and it was discovered that the inundation area is larger for higher resolution. Finally, the downstream inundation area is calculated, and outflow hydrographs at key sites are exported to ArcGIS from the RAS mapper in HEC-RAS for analysis. The maximum depth map, maximum velocity map, maximum water surface elevation map, and minimum flood wave arrival time map were created for various bridges along the river on the downstream side of the dam.