Click here to read the summary. Here’s an excerpt:
The Colorado River District owns and operates the Ritschard Dam forming Wolford Mountain Reservoir near Kremmling in Grand County. It is a clay-core, rock fill dam that has experienced settling beyond the amounts normally expected by designers for a dam of this type.
The dam is safe and will connue to be safe in the future, according to the District’s engineering staff. Engineering consultants engaged by the Colorado River District to study the problem since 2009, as well as the Dam Safety Branch of the Colorado Division of Water Resources agree that the dam is safe and poses no danger.
To maintain that standard, after an aggressive five-year investigation that included installation and monitoring of sophisticated instruments to measure the movements, the Colorado River District will decide this year on a renovation and repair scenario.
Since the dam was constructed in 1995, it has settled near its center by about two feet, a foot more than anticipated. Along with this settlement, the crest of the dam has shifted downstream by about eight inches.
Engineering consultants engaged by the Colorado River District to study the problem since 2009, as well as the Dam Safety Branch of the Colorado Division of Water Resources say the dam is safe and poses no danger.
Out of an abundance of caution, Colorado River District Chief Engineer John Currier said enough informaon has been compiled to identify by mid-year the repair options and advise the Colorado River District Board of Directors on the proper one to choose.
Consultants from AECOM (formerly URS) and River District staff briefed the Board of Directors on the condition and analysis of the dam at its January quarterly in Glenwood Springs.
“We as a staff think it is incumbent upon us as an organizaon to really start moving this issue down the road,” Currier said. He noted that computer modeling of the selement suggests that in future years, safety might be compromised, so a solution will be identified this year.
Although Colorado’s chief of dam safety has not placed an operational restriction on the dam, the Colorado River District will continue with the cautionary policy it began in 2014. Once the reservoir fills this spring, it will be immediately lowered by 10 feet in elevation. The lower water level has been shown by instrumentation to slow down settlement trends.
According to Currier, at that lower level, the Colorado River District can still meet its water contracting delivery needs, as well as obligations to endangered fish releases to the Colorado River.
Also still protected is Denver Water’s leasehold interest in a portion of the storage that it employs in dry years to compensate for water it stores in Dillon Reservoir out of priority over Green Mountain Reservoir. At 10 feet down, recreational use will not be adversely affected.
By the Board’s quarterly meeting in July, AECOM and staff will have repair scenarios to consider, including comparative costs.
AECOM engineers told the Board that the culprit in the settlement was a poorly compacted rock fill shell that surrounds the clay core on the upstream and downstream sides.
In such a dam, the clay core material is the impervious element in the dam. The rock fill shell supports the core. All dams, whether concrete or earthen, seep water.
At Ritschard Dam, filters meant to collect seepage are in excellent shape and are doing their job. Seepage does not show any effects from the settlement, Currier said.
More Colorado River District coverage here.