Dam Breach Analysis and Remedial Measure for Gilgel Gibe dam
No Thumbnail Available
Date
2016-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
This study mainly focuses on dam breach analysis and remedial measure of Gilgel Gibe dam. Gilgel Gibe Dam is a rock fill dam with 37 m height and 1,704m crest long and designed to generate hydro electric power. Generation of hydroelectric power has crucial part in the development of the country. In order to have medium power generation of Gibe as it is, it is necessary to study dam breach analysis and take remedial measures if it is needed. Generally this work focus on predicting the breach outflow hydrograph of Gilgel Gibe and routing it through downstream valley by applying computer programs to determine consequences/risk of dam failure and mitigate it. In analyzing dam breach the essential breach parameters involved in reservoir routing and river routing techniques were estimated manually outside the software. Breach parameters involved in routing process includes time to failure, side slope of breach, bottom breach width, manning roughness coefficient, shape of breach and boundary condition. The unsteady hydraulics of the dam breach due to piping and overtopping failure mode was modeled using U.S. Army Corps of Engineers HEC-RAS 4.1 software. The model results show a peak flow of 10,938.43 m3/sec and 8,700.57 m3/sec at the dam for both overtopping and piping failure, respectively. The failures of dam occur through piping as well as overtopping. The overtopped depth is 57 cm.
To route the downstream valley both hydrologic and hydraulic routing were undertaken. Hydrologic routing employs the continuity equation and an analytical or an empirical relationship between storage within the reach and discharge at the end where as hydraulic routing employs the continuity equation and both energy and momentum balances to calculate open channel flow profiles. Floodplain mapping for the downstream of Gibe Dam was performed using the water surface elevations on the XS cut lines, within the limits of the bounding polygon. Global and local sensitivity analysis was performed at downstream valley and dam site, respectively. Global sensitivity analysis was performed using manning roughness coefficient and channel bed slope. whereas the local sensitivity analysis was performed using time of the dam breach, side slope of beach, the bottom breach width and relative effect one on other. The model result show that breach formation time is highly sensitive than side slope of breach and bottom
Description
Keywords
Generation of hydroelectric power