Colorado partially lost a historical site in Hinsdale County amid flooding and safety concerns.

According to Hinsdale Unified Coordination Group, the Hurd family (Hidden Treasure Dam owners), along with an advisory board evaluated the potential risk for flooding and debris blockages among two dams – Ute Ulay and Hidden Treasure.

The main concern was debris blockages due to unprecedented avalanche activity could cause the dams to collapse, sending a dangerous surge of water and debris flow into Lake City.

The advisory board consisted of the Bureau of Land Management, Colorado Office of Emergency Management, Hinsdale County, the Town of Lake City, Colorado Geological Survey, and the Colorado Division of Water Resources’ Dam Safety division.

Hidden Treasure Dam before partial deconstruction, Photo Credit: Hinsdale Unified Coordination Group

After careful evaluation and assessment of the dams, the advisory board determined that the Ute Ulay dam posed little threat due to its fragile structure and large opening. However, Hidden Treasure dam posed a much greater risk for flooding and avalanche debris due to its sturdy structure and tiny opening. Upon these reasons, the board made the difficult decisions to deconstruct Hidden Treasure Dam.

As seen below, deconstruction of the Hidden Treasure dam using a robotic jackhammer began on Thursday, May 30, 2019, which reduced the height of the dam by 30-feet. Colorado Dam Safety Office Engineers then reevaluated the dam in an effort to avoid total dam deconstruction

To significantly reduce the threat of debris plugging, a large section from the bottom of the dam needed to be removed. Engineers guided contractors to use blasting operations. Using this modified approach, 48 holes were drilled and over 200 pounds of explosives were used to create a 14 x 28-foot opening in the dam above the river.

Blasting techniques not only helped preserve Hidden Treasure Dam for future generations to enjoy, but it also helped reduce environmental impacts by preventing large chunks of concrete from being blasted into the Henson Creek Channel.

Engineers and construction workers carefully evaluate Hidden Treasure Dam amid flooding and debris risks, Photo Credit: Hinsdale Unified Coordination Group

Dating back to the 1890s when both the Hidden Treasure and Hard Track mines were in operation, Hidden Treasure Dam was built to provide the Ute-Ulay mine with electric and water power. The dam broke in 1973, resulting in the sudden deaths of hundreds of fish approximately 14 miles downstream from toxic metallics and chemicals.

Hidden Treasure Dam before partial deconstruction, Photo Credit: Hinsdale Unified Coordination Group

Ultimately, the combination of lowering the top of the dam and creating a larger opening mitigated the threat of Hidden Treasure Dam to the Lake City community.

The partial deconstruction of the Hidden Treasure Dam was funded by a Natural Resources Conservation Service Emergency Watershed Protection grant, which covered 75% of the costs up to $938,000. Remaining costs were funded by Hinsdale County and the State of Colorado Disaster Emergency Funds.

Due to potential flooding risks, Colorado governor Jared Polis declared a state of emergency in Hinsdale County. While there are no evacuation orders in effect at this time. Emergency warnings, evacuation plans, and zones have been established. For more information, click here.

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