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Title: Dam Breach Analysis and Remedial Measure for Gilgel Gibe Dam
???metadata.dc.contributor.*???: Asie Kemal (PhD)
Million, Teshome
Keywords: Gilgel Gibe dam;Dam Breach;Remedial Measure
Issue Date: Dec-2016
Publisher: AAU
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 m 3 /sec and 3 8,700.57 m /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 breach width. Similarly the manning roughness coefficient is more sensitive than channel bed slope for downstream reaches. Overtopping and piping failure reduction measure had been conducted to reduce the risk occur due to the failure of dam. Covering crest and d/s face of dam, u/s watershed management, vegetation and provision of stone pitching, increasing spillway capacity and crest width and free board increasing were the measures undertaken to reduce risk of overtopping dam failure. Piping dam failure mode reduction were rock toe, chimney drain, u/s face impervious blanket, impervious cutoff, relief walls drain trenches and grouting affected zone. Generally ,the failure of Gibe dam affect the government, community living around the dam ,environment through loss of life, economy loss ,damaging property and inundating the flood prone area. Generally, the process of dam breach analysis and remedial measures for Gilgel Gibe dam as study case are discussed in this paper.
Appears in Collections:Thesis - Hydraulics Engineering

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