Dam Break Analysis (The Case Study of Nashe Dam)
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Date
2015-08
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Addis Ababa University
Abstract
Nashe earth fill dam was constructed in recent time for the purposes of hydroelectric power and irrigation. During construction of this project the peoples around Dam was resettled at different places including the downstream of the dam. This research focused on the dam break analysis on downstream of Nashe Dam if it breaks by overtopping and piping failure mode.
For this research the input data were collected from Water and Energy Minister of FDRE concerning the dam, breach parameters are calculated by Von Thun and Gillette and the cross- sections were from Digital elevation model (DEM) for hydraulic engineering model.
In dam break analysis the first step is model setup by using cross sections. After that the flow data, breach parameters and other such as boundary values are inserted as input data in the HEC-RAS model and the model result is exported to Arc-GIS for inundation map.
The peak discharge by overtopping mode is 8761.23m3/sec which is 7.33 times greater than the probable maximum flood and by piping mode of peak discharge 8620.85 m3/sec which is 7.21 times greater than probable maximum food at the location of the dam. This means that the maximum peak discharge out flow and risk due to overtopping is greater than maximum peak out flow and the risk of failure by piping mode. We observe the difference in the peak discharge values as the dams have the same storage capacity. The reason behind that is since the breach parameter is the same; the inflow discharge flood (IDF) which is used as upper boundary condition plays the crucial role in the development of peak out flow difference. So we can conclude that dam break by overtopping mode will develop high peak out flow and risk to downstream compare to dam break by piping mode. As from the sensitivity analysis we conclude that the effect of breach time on discharge is much pronounced than the water level. This is because of that the increment of water level is insignificant since the surface is flat and it flows to the both side and the top width is increased. Even if the degree of sensitivity analysis of other parameter is less than breach time, their effect on discharge is more pronounced than the water level.
Our Dam Break modeling results can be used as flood hazard maps and can assist communities in planning future developments in areas that are prone to flooding.
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Dam Break Analysis