Prediction of Impacts Associated with Reservoir Sediment Management
* Can Reclamation develop environmentally acceptable, efficient methods to manage sediment in our reservoirs?
* As Reclamation's dams age and as sediment continues to fill our reservoirs, what are the best tools and methods to predict the impacts associated with a variety of sediment management strategies?
Need and Benefit
As Reclamation's dams age, sedimentation becomes a major hindrance to their sustained use. More efficient methods to decrease sedimentation are necessary because mechanical dredging costs can quickly become unmanageable. In addition, as some dams become obsolete or not cost effective, Reclamation must decommission them in the most efficient manner possible. In both of these cases, allowing the river to transport sediment can be the most cost effective solution. To plan sediment releases appropriately, a model must be used to predict the possible impacts. These impacts may be positive or negative. For example, the sediment releases may improve habitat in sediment starved reaches downstream of dams. However, un-managed sediment releases may increase the flooding potential or temporarily destroy habitat.
Potential large releases of sediment will occur during the removal of Elwha and Glines Canyon Dams on the Elwha River near Port Angeles, Washington and the removal of Matilija Dam near Ventura, California. Several small dams are also being considered for removal or have been removed. Some examples are Saeltzer Dam and Battle Creek Diversion Dams in California, and Savage Rapids Dam in Oregon. Black Canyon is an example of dam where sediment releases may be necessary to extend the dam's useful life. East Park Dam is an example of a dam with severe sedimentation problems and where sediment releases could improve its water storage capacity.
A large obstacle to releasing sediment downstream is the uncertainty associated with its impact. Managers and stakeholders do not want to have a liability risk as a result of dam operation. Therefore, they may use a more costly mechanical or structural alternative to eliminate risk. However, such practices may cost millions of dollars and take money away from other necessary functions Reclamation performs. These problems will increase in both frequency and magnitude as dams age. Reclamation must have the best tools available to be prepared to face such problems. A better numerical model will reduce the uncertainty associated with large sediment releases and potentially save millions of dollars.
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This information was last updated on March 12, 2014
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