Estimation of the rate of sediment transport into the Bui hydropower reservoir

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June, 2016
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The knowledge of sediment yields in water infrastructures like reservoirs is necessary to be able to plan for long-term water resources development and management. The Black Volta Basin houses the recently constructed hydropower reservoir at Bui, which supplies 400 MGW of power to the national grid, but lacks recent sediment information for outstanding changes in sediment transport and sedimentation in the Bui reservoir. This study analysed the current rate of sedimentation in the Bui reservoir by establishing discharge and sediment rating curves at Chache (upstream of the reservoir) and Bamboi (downstream of reservoir), and using empirical equations together with suspended sediment data collected through a one year (2014/2015) monitoring programme. The results show maximum suspended sediment concentrations of 328.15 mg/l and 51.28 mg/l measured at Chache and Bamboi, respectively. This gives an indication that the Bui reservoir is effective in trapping sediment from upstream of the reservoir catchment area. Current gross annual sediment yield in the reservoir was estimated at 1,370,007 t/yr. Compared to the designed rate of sediment yield for the reservoir (968,000 t/yr), the current estimate depicts an increase in annual sediment yield of about 41.5 %, which has negative impact on hydropower generation, aquatic life including fishery, and the lifespan of the reservoir. The increase in sediment yield over the designed figure could worsen in the near future if changes in land use, particularly illegal small scale mining activities upstream and close to the reservoir are not properly managed by regulating or enforcing the laws governing illegal small scale mining.
A Thesis submitted to the Department of Civil Engineering, College of Engineering in partial fulfilment of the requirements for the degree of Master of Science Water Resources Engineering and Management.