Dam breach modelling and flood inundation mapping of an earth embankment dam using HECRAS:

Abstract

Analysis and simulation of embankment dam breach events and the resulting floods is critical to differentiating and reducing threats due to potential dam failures. Development of effective emergency action plans requires accurate prediction of inundation levels and the time of flood wave arrival at downstream critical locations. Embankment dams are commonly built in Uganda as they provide benefits to the local population, mainly agricultural activity and generation of hydropower. However, its massive potential energy reservoir would impose risk of sudden containment breach leading to loss of life and property at inhabited downstream area. This research is deemed to provide a dam break analysis of Bujagali Dam to generate breach hydrograph and inundation map as a result of dam break event under overtopping failure. The Hydrologic Engineering Center’s River Analysis System (HEC-RAS) is capable to model 1-dimensional (1-D) and 2-dimensional (2-D) dam failure event by utilizing hydrological and terrain information generating unsteady state flow simulation of the dam breach. The process for gathering and preparing data, estimating breach parameters, creating one dimensional and two-dimensional unsteady-flow model in HECRAS, performing a dam failure analysis for dam failure scenario and mapping the flood propagation are outlined in this paper. From 2-D analysis, it is found that the breach flow of Bujagali Dam failure can achieve 14,277.84 m3/s for overtopping failure. Furthermore, the expected arrival time of flood wave at selected locations also presented in this paper. However, 2-D model was able to generate inundation map due to dam failure in wider area which can provide insight of flood hazard risk level, the simulation results were mapped using the GIS extension tool on ArcMap. Inundation mapping of water surface profile result from dam failure models provides a level of the flood hazard and provides insight for emergency action plan. Key Words: Dam Breach, Modelling, DEM, HEC-RAS, Hydrograph, Inundation