Echo Dam retrofitted for major earthquake
July 20, 2012
When Utahns practiced for a massive earthquake during "The Big Shakeup" two months ago, they didn’t prepare for the liquefaction of Echo Dam and the deadly consequences that could follow. But due to a large project by the Federal Bureau of Reclamation, the dam’s destruction in an earthquake may no longer be a threat.
According to Bureau of Reclamation Area Manager Curt Pledger, Echo Dam, located about seven miles north of Coalville, was built in the 1930s to provide residents with more water from the Weber River.
Pledger said that during one of the comprehensive inspections of the dam in 1999, it was discovered that if a high magnitude earthquake struck along the Wasatch Front fault, the materials underneath the dam could liquefy.
"Liquefaction is a new phenomenon that we really just began to understand in the 1990s," Pledger said. "What it means is that loosely deposited soil under the dam becomes saturated with water and then when it is shaken by an earthquake it turns from a solid to a liquid and loses all of its strength, causing the dam to slump."
A major fault line runs along the Wasatch Front and Pledger said another one runs along East Canyon near Henefer, making it likely that the dam may have to withstand an earthquake someday.
Bureau of Reclamation Program Coordinator Jonne Hower said that a contract was awarded to local contractors PnK Construction in 2011 to remove the water from the dam’s foundation, excavate the material from under the dam and replace it with stronger, denser material.
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"They began removing water and doing some excavation this year," Hower said. "The first phase of the project is expected to be completed next summer and then they will make some improvements to the spill way. Overall the project will be done in December 2014."
Hower added that there were no immediate problems with the dam and officials wanted to bring it up to current standards.
Jimmie Keyes, president of PnK Construction in Coalville, said that while his company has worked on dam-retrofitting projects before, the Echo Dam project is unique.
"Primary concerns or risks working on dams are vast, including what types of materials are encountered and how much ground water will be present when removing the dam embankment," Keyes said, adding that the materials that are used in the project must also fit the Bureau of Reclamation’s strict requirements.
According to Pledger, the project is ahead of schedule by six weeks due to the low water level in the reservoir this year.
"We thought we would need to wait until mid-June for the water to reach a low enough level so we could begin construction," he said. "But due to the low runoff this year and farmers needing extra water for irrigation, the water was at a low enough level by June 1. Right now, the reservoir is only at one-third capacity."
Pledger added that once the improvements are complete, the dam will be able to withstand a 7.5 magnitude quake on the Wasatch Fault and a 6.5. magnitude quake on the fault near East Canyon.
"The fault line in Summit County is not as large as the one in Salt Lake, but if an earthquake happened on it, it would place a larger load on the Echo Dam," Pledger said. "We want this dam to be able to withstand an earthquake anywhere."
The Echo Dam project is estimated to cost $50 million. Hower said the Bureau of Reclamation will pay for 85 percent of the project and the Weber River Water Users Association will pay the other 15 percent.