River Sediment Transport Monitoring to Improve the Life Span of Dams

Mehamed, Sied Znabu (2014) River Sediment Transport Monitoring to Improve the Life Span of Dams. Masters thesis, Addis Ababa University.

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Abstract

With reasonable levels of maintenance, the structural life of dams is virtually unlimited. Most reservoirs are designed and operated on the concept of a finite life which ultimately be terminated by sediment accumulation rather than structural obsolescence. In Ethiopia sedimentation has theoretically been expected to be controlled through watershed management practices, however the story behind dams like Koka, Angereb, Legedadhi, and Gilgel Gibe-I, which are threatened by an accelerated sedimentation, tells a different approach is needed in monitoring the sedimentation of reservoirs. River sediment transport towards a reservoir monitoring can achieve through implementing upstream silt traps, bypassing heavily sediment laden flows, reservoir drawdown and flushing, density current flushing etc. Ethiopian rivers usually contain a larger sediment concentration at the beginning of the rainy season. Thus among the approaches of monitoring sediment inflow to a reservoir, bypassing days of heavily sediment laden flows was analyzed in this study for its practicability on newly constructed KesemKebena, Tendaho and Rib dams. Such sediment control measure enables to reduce annual inflow of sediments to a reservoir on the expense of losing the water that would join the reservoir. The merits and demerits of using storage approach tool and benefit cost analysis based on the income of the project, are comparatively tasted on those three Ethiopian dams for both effects of the dam storage and the improved life span of the dam. The result showed that, by passing the days of flow of August, August & September, August & July for Kesem Kebena, Tendaho and Rib dams, respectively will bring about more reasonable benefit than letting the river‟s flow in these months to the reservoir. By passing a day of river flow in August will improve the life span by 2.1 year for Kesem, 0.7 year for Tendaho and 0.9 year for Rib dam. The extended life span of the dams has net storage benefit of 454 million cubic meters (MCM), 788 MCM and 50 MCM, for the three dams, respectively. The cost benefit analysis of a day of August flow by passing has benefit cost ratio of 4.3, 2.7 and 1.7, respectively. However, the result shall be seen with caution that it does not considered the possible sediment volume reduction by watershed management practices. Thus, the research also put some directions of monitoring techniques; however, to select the most suitable sediment treatment method shall be decided with the consideration of topography and flows of river, effectiveness, economic, environmental and various conditions.

Item Type:	Thesis (Masters)
Uncontrolled Keywords:	Kesem- Kebena Dam, Life Span of Dams, Ribb Dam, Sediment by passing, Sediment Transport Monitoring, Sediment Transport, Tendaho Dam, Reservoir Sedimentation, Benefit Cost Analysis
Subjects:	G Geography. Anthropology. Recreation > GE Environmental Sciences Q Science > QE Geology T Technology > TA Engineering (General). Civil engineering (General) T Technology > TC Hydraulic engineering. Ocean engineering T Technology > TD Environmental technology. Sanitary engineering
Divisions:	Africana
Depositing User:	Andriamparany Edilbert RANOARIVONY
Date Deposited:	27 Nov 2018 13:13
Last Modified:	27 Nov 2018 13:13
URI:	http://thesisbank.jhia.ac.ke/id/eprint/7745

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