Developing Guidelines for Formulating Reservoir Sustainability Plans
Project ID: 6080
Principal Investigator: Kent Collins
Research Topic: Sediment Management and River Restoration
Funded Fiscal Years: 2013
Keywords: reservoir sedimentation, reservoir sustainability, sediment management, flood storage, reservoir operations, design life, useful life, reservoir survey
Reclamation dams and reservoirs serve a wide variety of useful purposes such as water supply, hydropower, flood control, recreation, and fish and wildlife. The loss of reservoir storage and dam functionality due to sediment deposition is a critical issue for Reclamation's future. Reservoir sedimentation reduces storage capacity at all reservoir elevations; increases upstream flood stage; can impair the operation of dam outlets, water intakes, boat ramps, and marinas; and reduces the surface area available for recreation. In addition to sedimentation issues within the reservoir, a reduced sediment supply to the downstream river channel can result in channel incision/degradation, bank erosion, coarsening of the stream-bed material, and impacts to aquatic and terrestrial habitat.
This research proposes to develop guidelines for the formulation of reservoir sustainability plans for the effective management of inflowing sediment loads and in-situ deposits by answering two key questions:
1. What is the process for developing a plan and strategy for the managing sediment inflow and deposition in Reclamation reservoirs? Sedimentation occurs at all reservoirs at various rates and sedimentation eventually impacts reservoir facilities and storage capacity. Taking a proactive approach to managing reservoir sediments provides the best chance for extending the useful life of any reservoir.
2. What is the best method for identifying which Reclamation reservoirs present the highest risk for experiencing adverse operational impacts and pose the greatest need for implementing an appropriate sustainability plan? Many Reclamation reservoirs in multiple Regions have experienced or are experiencing operational challenges due to a variety of sediment deposition issues. Early identification of sediment related problems and proactive implementation of a customized sustainability plan are vital components in the preservation of a dam or reservoir's ability to meet Reclamation's mission.
Need and Benefit
The urgency of mitigating the impacts of sedimentation on reservoir storage and dam operations is often stifled by the hidden nature of the problem. Regardless of volume or extent, reservoir sediment deposits often cannot be seen through the water by the naked eye and are therefore ignored. Failure to measure or estimate sediment inflow or deposition rates can result in severe impacts including the loss of reservoir storage capacity, burial of outlet works, burial of recreational facilities, downstream erosion, and habitat loss. For example, the reservoir behind San Clemente Dam on the Carmel River in California is now full of sediment and the cost to remove the dam and contain the sediment is $80 million (Randle, 2010). A large percentage of Reclamation reservoirs have already been impacted on some level by sediment deposits in the delta, historical river channel, or near the dam, yet only about 35 percent of Reclamation's 300 plus reservoirs have been resurveyed since initial filling. Of those that have been resurveyed, the majority fall in the 0 to 5 percent capacity loss category (Ferrari, 2005). However, Reclamation Dams were designed to accommodate sedimentation over the first 100 years of operation. After that time, sedimentation can be expected to impair the lowest outlets of a dam (Bureau of Reclamation, 1987) and other reservoir facilities. By 2020, at least 54 reservoirs will be at least 100 years old (Randle and Ferrari, 2010). With many Reclamation reservoirs at or near their sediment design life, future sediment inflows will further decrease operational capabilities of these facilities along with the reservoir storage capacity.
Examples of dams and reservoirs that are experiencing sedimentation problems are listed below. Some of these reservoirs have had previous studies performed that will be integral in creating a framework of options and new alternatives in achieving reservoir sustainability.
Reservoirs that have sedimentation problems (Randle and Ferrari, 2010; Hepler, 2005):
1. Loss of Reservoir Storage Capacity: Paonia Reservoir, CO; Elephant Butte Dam, NM; Matilija Reservoir, CA.
2. Burial of Outlet Works: Belle Fourche Reservoir, SD; Sumner Dam, NM; Horseshoe Dam, AZ; Arrowrock Dam, ID; Lake Sherburne Dam, MT; Twitchell Dam, CA.
3. Loss of recreational facilities: Horseshoe Bend Boat Ramps, Bighorn Reservoir, WY; Black Canyon Dam, ID; Hite Boat Ramp, Lake Powell, AZ.
4. Downstream Channel Erosion and Habitat Loss: Fort Sumner Dam, NM; Platte River, NE; Lake Powell, AZ.
Reservoirs that have sediment management programs (Randle and Ferrari, 2010):
1. Flood and Sediment Bypass Tunnel: Miwa Dam, Japan
Taking a proactive approach in developing a reservoir sedimentation management strategy for Reclamation reservoirs will help avoid loss of project benefits and expensive retirement options. The annual cost to manage inflowing reservoir sediment is much less than the cost of trying to recover decades of past reservoir sedimentation. The "no action" strategy to reservoir sediment management will eventually lead to the retirement of Reclamation reservoirs that no longer provide water storage benefits. A proactive and sustainable approach to reservoir sediment management would mean that a reservoir would be able to provide project benefits indefinitely. A sustainable sediment management strategy would require upfront and continual operational & maintenance costs (including monitoring), but these continual costs can be feasible and less than the final costs associated with dam decommissioning. Methods and alternatives identified by this research will help determine the state of Reclamation facilities relevant to reservoir sedimentation impacts and will provide Reclamation and other Federal agencies with an application for taking a proactive planning approach to best manage dams and reservoirs in a sustainable manner.
This information was last updated on December 8, 2013
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