Achieving Reservoir Sustainability
Project ID: 2943
Principal Investigator: Kent Collins
Research Topic: Sediment Management and River Restoration
Priority Area Assignments: 2012 (Climate Adaptation), 2013 (Climate Adaptation)
Funded Fiscal Years: 2012
Keywords: reservoir sustainability, sediment management, flood storage, reservoir operations, design life, useful life, reservoir survey
Reclamation facilities serve a variety of useful purposes such as water supply and delivery, flood storage and attenuation, and recreation. The loss of reservoir storage and dam functionality due to sedimentation is a critical issue for Reclamation's future. Reservoir sedimentation reduces storage capacity at all reservoir elevations; increases upstream flooding; can impair the operation of dam outlets, water intakes, boat ramps, and marinas; and reduces the surface area available for recreation. This research proposes to compile existing options and formulate new alternatives for the effective management of inflowing sediment loads and in-situ deposits to improve reservoir sustainability by answering two questions:
1. What are the options for managing sediment inflow and deposition in Reclamation reservoirs? Existing literature provides limited information on the types of reservoir sedimentation issues impacting reservoir storage and dam operations and few recommendations on dealing with such issues. Once a dam closes and the reservoir it contains begins to fill, inflowing sediment begins to deposit, and operators will eventually be forced to deal with the associated issues. Taking a proactive approach to managing reservoir sediments, including analysis of potential alternatives, provides the best chance for extending the useful life of a Reclamation reservoir.
2. What level of effort is required to achieve sustainability in various types of Reclamation reservoirs? There is a wide variety of possible alternatives for improving reservoir sustainability. Time and budget constraints limit the range of plausible options. The type of reservoir and scope of the sediment problems it is experiencing further narrows the list of technically feasible alternatives. The amount of funding and effort expended to extend the useful life of a reservoir must be less than or equal to the benefit received from any such project, including the avoidance of future retirement costs.
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 30 percent of Reclamation's 400+ 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 (Reclamation, 1987). 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; 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 reactive approach in developing a reservoir sedimentation management strategy for Reclamation reservoirs will lead to expensive and likely infeasible alternatives. 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 operation and maintenance costs, 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 provide Reclamation and other Federal agencies with a format for discussion of pressing reservoir sedimentation issues. The methods and alternatives will enhance the platform of taking proactive management measures to best manage dams and reservoirs in a sustainable manner, getting the most benefit of water resources from a long-term economic and environmental perspective.
Bureau of Reclamation Review
The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.
Formulating Guidelines for Reservoir Sustainability (interim, PDF,
By Kent Collins, Tim Randle and Sean Kimbrel
Report completed on September 30, 2014