Water

Dams and Development E-Paper Contents

p. 48 of 74 BACK | NEXT Home Page of Dams and Development Foreword I. Why an e-paper on dams and development? II. Assessing options III. Participatory processes IV. Social impacts V. Environmental impacts VI. Benefit distribution VII. Dam safety and sustainability Dam safety Operation in times of flood Reservoir quality Managing sedimentation VIII. Existing projects IX. Improving governance X. What other organizations say XI. ADB, Dams, and Development XII. References Contact Us

Managing sedimentation to prolong reservoir life

Sedimentation rates in reservoirs vary considerably depending on location (catchment topography, land use, climate etc) and reservoir design and operation.

The worldwide average for the loss of storage due to sedimentation is reported to be between 0.5% and 1.0% per annum although this masks high variability, even among reservoirs in the same region.

Consideration is needed not only to the absolute volume of sediment and its impact on storage capacity, but also the distribution of sediment and the effect it can have on operation of power intakes or water offtakes.

Important factors influencing the sedimentation process categorized are:

• Fluctuations in water and sediment inflow
• Sediment particle size distribution
• Reservoir operation cycle
• Physical controls or the shape and size of the reservoir

Methods to minimize and manage sediment accumulation are summarized in a number of standard texts and in Thematic Review V.5 Operations, Monitoring and Decommissioning of Dams prepared for the WCD. They include:

• Selection of dam location and operation
• Land use and soil conservation
• Upstream diversion or bypassing of sediment laden water
• Sediment trapping
• Sluicing
• Density current venting
• Excavation
• Flushing - a relatively new technique suited to certain reservoir layouts and flow characteristics.

More details can be found at:

• ICOLD Bulletin 115 dealing with sedimentation
• Sediment Flushing - Evacuation of sediments from reservoirs

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