Dam Breach Analysis and Flood Inundation Mapping For Lower Awash Multipurpose Dam

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Addis Ababa University


Dam breach analysis is essential for investigating future effects posed to human life and property by a sudden release of water to the inundation area downstream of a dam. Every constructed as well as proposed dams need to be analyzed for the possibility of dam breach to clearly identify the extent of catastrophic effects associated with their failure. The aim of this study is to model the dam breach at the proposed Lower Awash Dam for the development of flood inundation maps used to emergency action plans. The proposed dam is located in Afar National Regional State on Logia River at about one hundred kilometers upstream from the bridge on Logia River of main road to Djibouti. The analysis was performed for piping failure scenario using HEC-RAS two dimensional unsteady flow modeling. The inflow hydrograph was taken as an upstream boundary condition for the unsteady flow simulation. The model was calibrated for the flow years (1998-1999) and its performance was evaluated for the year 2001. The flood inundation and flood hazard maps were prepared by exporting the tiff raster files from RAS Mapper to ArcGIS and overlying to ArcGoogle to visualize coverage of the flood prone area due to the breach. The resulting breach parameters were 146 meters breach bottom width, 1.17 hours breach formation time, and 0.5 breach side slope (H:V). The simulated results on HEC-RAS reached peak breach outflow discharge of 60,072 cumecs. Through model calibration close agreement has been arrived between model simulated and observed rating curves at Logia gauging station. As noticed from the flood inundation and flood hazard maps an extended area in the flat plains downstream of the dam would be affected due to the breach with a maximum flood depth of 21.6 m. Therefore, the flood inundation and flood hazard maps could be adopted for proper emergency action plans that have to be taken by stake holders.



Lower Awash, HEC-RAS, ArcGIS, RAS Mapper, Dam Breach, Inundation Map