Dam Break Analysis Using HEC-RAS Model The Case Study of Gilgel Gibe 1

Abstract

Floods due to failure of dams induce widespread damages to property and losses of life and owing to its high magnitude and unpredictable sudden occurrence. The objectives of the study is to analyze, and evaluate the impact of 100 year flood, and probable maximum flood as inflow scenarios as well full reservoir pool sunny day failure, the objectives of the study is achieved by using two computer models. Upstream of the study dam , the catchment has been divided into three subbasins, namely upper subbasin, upper left subbasin, and upper right subbasin, Hydrological Engineering Center- Hydrological Model System developed for study area after determining the initial parameters, such as probable maximum precipitation, and one percent precipitation, the objective of hydrological model was to estimate probable maximum flood , one chance flood , and the result of the two scenarios applied to the dam in case of overtopping. Hydrologic Engineering Center -River Analysis System used to determine water surface profile, and simulate and predict peak flow, and outflow hydrograph for the three scenarios, model is used for dam breach analysis , dam failure were analyzed for probable maximum flood , one chance flood , and sunny day failure, breach parameters are determined by using two methods ,Bureau of reclamation (1982) and Thun Von & Gillette (1999). The result of the hydrological models showed that, there is no overtopping for the two scenarios , probable maximum flood, one chance flood, meanwhile the result of hydraulic model indicate that peak flow , and outflow hydrograph depend on the additional inflow, nature of the reservoir, and breach paraeters.