Dry year may help solve mystery of Wolford Mountain dam movement
Sky-Hi Daily News
KREMMLING – Engineers with the Colorado River District have stepped up monitoring activity on the dam at Wolford Mountain Reservoir in anticipation of a drawdown that may give them greater insight into why the earthen structure is shifting.
“This year is a really good test,” John Currier told Kremmling Town Board members Wednesday night, explaining that the reservoir will be drawn down 30-35 feet below full by the end of October.
“The reservoir hasn’t been drawn down like this since 2002-2003,” he added.
Currier, chief engineer for the river district, was at the meeting along with other district representatives to allay rumors that Wolford Mountain is being drawn down to prevent it from failing and to present a progress report about the ongoing investigation into why the dam is moving.
He said the reason the reservoir will be drawn down so far this fall is that Denver Water, which holds a lease for 25,000 acre-feet of “substitution water” annually in the 66,000 acre-foot impoundment, will release all its water this year. That, and Colorado Parks and Wildlife will use another 6,000 acre-feet this fall to augment downstream flows for endangered fish, he said.
In a “normal” year, he said the reservoir is drawn down about 10 feet. When that occurs, he said monitoring instruments indicate the rate of settling slows substantially. What engineers will be looking at this fall is whether there is a point at which the settling slows further or stops as the water level falls.
Currier said engineers first discovered the movement in 2008, when they noticed the crest of the dam had settled more than anticipated. Original estimates indicated the 120-foot-high structure would settle about 6 inches to 1 foot.
It has now settled nearly 2 feet, Currier said, and it is continuing to settle at a rate of about 1 inch annually. There is also slight (just over 6 inches) downstream movement in a section of the dam between 40 feet and 60 feet from the top on the downstream “shell” of the structure. That area is moving a “couple hundredths of an inch” per month, he said.
“The question is, is how much (movement) is too much?” Currier said. “That’s something we really don’t know.”
“The dam is safe,” he emphasized. “It’s not leaking, but it is moving. … We’re confident in the safety of the dam.”
Nevertheless, “We’re very concerned,” he added.
The river district has already spent more than $1.2 million investigating the problem, and district officials say the issue has serious ongoing financial implications.
Grand County Commissioner James Newberry, who represents the county on the river district board, reiterated that the Wolford settling will be among the top financial issues for the district in coming years.
He also noted the value of the reservoir locally and regionally, explaining that this year discharges from the reservoir have augmented flows in the Colorado River sufficiently to result in good rafting and fishing below Gore Canyon despite this being a low water year.
However, he said, “Something has to change” to stop the settling.
“I’m very happy you’re monitoring the situation more aggressively,” Kremmling Mayor Tom Clark told river district officials.
Currier said the river district has received a letter from the Dam Safety Branch of the Office of the State Engineer that says unless the district can demonstrate why the dam is moving and when it will stop, Wolford Mountain might have to operate with mandatory storage restrictions, none of which are in effect.
“We don’t really anticipate operating under a storage restriction,” he said, but it could become an option.
When the drawdown occurs this fall, Currier said, “We may use this (data) to determine that we want to run for the long term with a self-imposed storage restriction.”
Other options include partial reconstruction of the dam, he said, though that could be costly.
“I think, ultimately, we’re going to be … either operating at a lower level or getting in there and fixing it,” Currier said.
In the meantime, he said the settling problem has not led to any operational issues and there is no movement in the foundation of the structure.
Construction of the dam was completed in 1995.
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