Seismic Upgrade Work at Echo Dam Continues
While the well below average precipitation this water year is generally not good news for Utah reservoirs, the low water level in Echo Reservoir has facilitated seismic upgrade work at Echo Dam which is ahead of schedule.
This upgrade work is being done to ensure the dam, which was constructred according to 1930s standards, meets current seismic stability and engineering requirements. Studies conducted at Echo Dam since 1998 for the Bureau of Reclamation’s Safety Evaluation of Existing Dams Program indicated that potentially liquefiable materials are present within the dam’s foundation and underneath the spillway control structure.
Generally, liquefiable soils associated with dams are alluvium materials that are loosely deposited. If these materials are saturated by water and then shaken (as in an earthquake) the bonds between the particles of material are broken and replaced with water. The result is the material may behave as a liquid and lose strength. If a portion of the dam foundation were to liquefy, there may be slumping in the dam embankment and displacement of the spillway—potentially leading to catastrophic failure of the dam and reservoir.
Based on Reclamation’s continued investigations and completion of a Safety of Dams Modification Report approved by Congress in November, 2010, the dam safety work currently underway was initiated.
As part of the current upgrade work at Echo Dam, Reclamation has replaced the liquefiable materials in the downstream foundation of the dam. Crews are currently constructing the downstream stability berm that will buttress the downstream face of the dam and help the slope withstand an earthquake. Also, work is underway constructing a stability berm on the upstream face of the dam that serves the same purpose; completion is expected by October 1, 2012.
Reclamation recently awarded a $9.1 million contract to Gerber Construction, Inc. of Salt Lake City for the spillway improvement work at Echo. Under this contract, the spillway crest structure and portions of the chute will be demolished and rebuilt. The four large steel radial gates will also be removed and will undergo refurbishing and recoating before reinstallation. Another portion of the work will stabilize the foundation underlying the crest structure.
The work on the spillway is scheduled to take place between July 2013 and December 2014, however, the spillway will be usable by the spring runoff of 2014.
Completion of the estimated $50 million Safety of Dams modification is scheduled in 2014. Under Reclamation law, local water users (represented by the Weber River Water Users Association) reimburse Reclamation for just 15 percent of the cost of the modification over a 25-year period.
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Echo Dam is part of the Weber River Project that was authorized in 1927 to supply supplemental irrigation water to approximately 109,000 acres of land west of the Wasatch Mountains. Formerly designated the Salt Lake River Project, its principal feature is Echo Dam and reservoir located 42 miles southeast of Ogden, Utah, on the Weber River. Echo Dam, a zoned earthfill structure, was constructed between 1927 and 1931 and has an active storage capacity of 73,900 acre-feet. The dam is 158-feet high, 1,887-feet long, and contains more than 1.5 million cubic yards of earth embankment. A hydroelectric plant, installed in 1987, supplies the city of Bountiful, Utah, with up to 4.5 megawatts of power. The Weber River Water Users Association operates and maintains the project under contract with Reclamation.
Reclamation's Dam Safety Program was authorized in 1978 by Congress (by PL 95-578 as amended.) Echo Dam is the thirteenth large dam in Utah and southwestern Wyoming that has been modified by the Provo Area Office since the 1980s. Reclamation ensures that dams are operated and maintained in a safe manner by conducting regular and thorough inspections for safety. Analyses are completed utilizing current technologies and designs. Corrective actions are based on current engineering practices and standards.