Dam Breach Analysis Using HEC-RAS and HEC-GeoRAS: The Case of Kesem Kebena Dam
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Date
2015-12
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Addis Ababa University
Abstract
Dam breach analysis is generally used to predict flood on the downstream of the dam but also it is crucial to predict dam breach parameters, outflow hydrograph and its downstream nature of propagation. Results from dam breach analysis can be used to protect downstream population and it can also be used while designing and implementing future infrastructure. Kesem Dam, found in the Kesem sub-basin of Awash Basin in Ethiopia has been selected as a case study dam in this paper.
Within this study the dam has been checked for both overtopping and piping using one dimensional river analysis model HEC-RAS and empirical equations are used to predict dam breach parameters for the use in the model. PMF inflow with a peak 9237.77m3/s is used for overtopping failure. The spill way have adequate capacity for the flood due to the PMF and breaching of the embankment was not possible in HEC-RAS. Piping failure was simulated in HEC-RAS using breach parameters obtained from the empirical equations.
The modeling process was towards performing unsteady flow calculations in the intent of routing the breach outflow downstream of Kesem Dam from the dam up to the downstream boundary which is 60km from the dam. The models HEC-RAS and HEC-GeoRAS are used alternatively. HEC-GeoRAS extracts topographic data from Digital Elevation Model (DEM) and prepares geometric file in ArcGIS. The geometric file is imported into HEC-RAS. Using the geometric file and unsteady flow data (PMF inflow, initial flow and normal depth) unsteady flow calculation is performed in HEC-RAS. Geometric file with water surface elevation attached to it is exported to ArcGIS where HEC-GeoRAS uses it to prepare a flood map. The produced map is overlaid on an aerial map to see towns and infrastructures that are affected by the flood.
Key words: Dam Breach Analysis, Flood Mapping, HEC-RAS, HEC-GeoRAS
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Keywords
Dam Breach Analysis, Flood Mapping, Hec-Ras, HEC-GeoRAS