Grizzly Reservoir to be drained next summer for rehab work: Repairs planned for dam, tunnel, outlet works — @AspenJournalism

Grizzly Reservoir will be drained next summer for a rehabilitation project on the dam, tunnel gates and outlet works. The reservoir serves as the collection bucket for water from the surrounding drainages before it’s diverted through the Twin Lakes Tunnel to the Front Range. CREDIT: HEATHER SACKETT/ASPEN JOURNALISM

Click the link to read the article on the Aspen Journalism website (Heather Sackett):

Grizzly Reservoir, the high-mountain lake above Aspen formed by damming Lincoln and Grizzly creeks, will be drained next summer for repairs to the dam, tunnel and outlet works.

After spring runoff next year, Twin Lakes Reservoir and Canal Company will draw down the reservoir so workers can install a membrane over the steel face of the dam, which was constructed in 1932 and is corroded and thinning, according to a May report on the feasibility of the dam rehabilitation.

The report, by RJH Consultants, Inc. of Englewood, included an inspection and evaluation of the infrastructure, and presented different options for rehabilitation. Half the cost of the study — $50,000 — was funded by the Colorado Water Conservation Board.

The project will also replace the gates that control the flow of water into the Twin Lakes Tunnel and repair the outlet works that release water down Lincoln Creek. According to the report, the outlet works have issues with cracks, holes and seepage, and the more-than-80-year-old tunnel gates have problems with leakage, are difficult to operate and require significant maintenance every year.

“The purpose of the rehabilitation of the dam is to address dam safety concerns associated with the corroded and thinning upstream-slope steel facing, uncontrolled seepage, and operational problems with the outlet works,” the report reads.

Twin Lakes officials expect the project to be completed in October 2023. They will also draw down the reservoir this month to weld a small test portion of the dam membrane to see how it fairs through the harsh winter at 10,500 feet. That work is scheduled to begin Aug. 22 and the reservoir will be refilled in October.

“That infrastructure is aging and it’s time to do some rehab work on it,” said Twin Lakes Reservoir and Canal Company Board President Kalsoum Abbasi.

Grizzly Dam is considered a high hazard dam by the Division of Water Resources. That does not mean it’s likely to fail, but it means loss of life would be expected if the dam did fail. The last state inspection in 2021 found the dam satisfactory — the highest rating — and said full storage capacity was safe.

The report estimated a nearly $7 million price tag for the rehabilitation work. Twin Lakes plans to get a CWCB loan for some of the cost and will pay the remainder with money raised from assessments on its water users.

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