Hydraulic Measures for Unexpected Flood Control

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Addis Ababa University


Any hydraulic structure constructed across a river is designed based on a prior estimation of design flood. This design flood estimation needs a hydrologic parameter estimation through the entire catchment area and along the river course. Such parameters have never been estimated accurately. Moreover, the design discharge estimated will be exceeded due to climate change, uncertainty of design flood estimation methods, hydrologic data constraint and the like. Thus, the design flood estimated for the design of a hydraulic structure across a river has a high probability of being exceeded. A measure that should contain any unexpected flood, a flood beyond the design flood, should be devised. In this study, a hydraulic measure that utilizes river channel characters modification for containing the unexpected flood is practiced by taking 5.4km length of Kesem River which is found upstream of Kesem Kebena Dam as a case study. The study would improve the river flood storage character and reduce the unexpected flood that will come to the reservoir by changing the river channel character upstream before joining to the reservoir. In addition to this, there were also a number of channel character combination modifications to select the best combined river channel character improvement measures. Some of them were minimum slope and maximum roughness coefficient, average slope and maximum roughness coefficient, minimum slope and average roughness coefficient. Based on the result of the study, the minimum slope and maximum roughness coefficient and average slope and maximum roughness coefficient combination modifications have good flood storage result among the channel character modification combinations and these two measures have relatively similar flood magnitude reductions. The maximum flood that could be reduced through the implementation of these combined measures for 10,000 return period design flood of 9237m3/s was 0.38% and for the 100 years return period design flood of 3765m3/s was 0.53%. Therefore, for an effective and sustainable flood controlling measures for unexpected flood on a hydraulic structure, the need for reliable hydraulic measures are unquestionable. Key Words: Hydraulic measures, distributed flow, saint venant equation, unexpected flood, Kesem River, reaches, nodes, roughness coefficient and slope, Kesem Kebena Dam.



Hydraulic measures, Distributed flow, Saint venant equation, Unexpected flood, Kesem River, Reaches, Nodes, Roughness coefficient and slope, Kesem Kebena Dam