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12 - Reservoir sedimentation

Published online by Cambridge University Press:  05 June 2012

Pierre Y. Julien
Affiliation:
Colorado State University
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Summary

As natural streams enter reservoirs, the stream flow depth increases and the flow velocity decreases. This reduces the sediment transport capacity of the stream and causes settling. The pattern of deposition generally begins with a delta formation in the reservoir headwater area. Density currents may transport finer sediment particles closer to the dam. Figure 12.1 depicts a typical reservoir sedimentation pattern. Aggradation in the upstream backwater areas may increase the risk of flooding over long distances above the reservoir.

The rate of sedimentation in reservoirs varies with sediment production on the watershed, the rate of transportation in streams, and the mode of deposition. Reservoir sedimentation depends on the river regime, flood frequencies, reservoir geometry and operation, flocculation potential, sediment consolidation, density currents, and possible land use changes over the life expectancy of the reservoir. In the analysis of reservoir sedimentation, storage losses in terms of live and dead storage, trap efficiency, control measures and the reservoir operations must be considered given: the inflow hydrograph, the sediment inflow, the sediment characteristics, the reservoir configuration, the regional geography, and land use.

The concept of life expectancy of reservoirs describes the time at which a reservoir is expected to become entirely filled with sediment. Its evaluation represents a challenge since the sediment sources arise from various geological formations, cutting and burning of brushland and forest, over-grazed grasslands, natural hazards including landslides, typhoons, and volcanoes, and changes in land use are all likely to occur during the expected life of the reservoir.

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Publisher: Cambridge University Press
Print publication year: 2010

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