#Colorado’s dam safety examined

Horsetooth Reservoir
Horsetooth Reservoir

From The Fort Collins Coloradoan (Jacy Marmaduke):

The good news: All of Larimer County’s biggest dams, including the dams at Horsetooth Reservoir, have emergency action plans designed to prepare authorities for emergencies like what happened in California this weekend.

And the bad: A small percentage of Colorado’s higher-hazard dams don’t have emergency plans. Failure could put human lives, environment and property at risk.

It’s a problem highlighted nationwide this week after the Oroville Dam, located about 75 miles north of Sacramento, suffered a potential failure of its emergency spillway. While the dam itself remained intact, erosion damage to the spillway raised the possibility of the structure failing and unleashing an uncontrolled torrent of water.

This situation is unlikely to occur at any of the Horsetooth Reservoir dams, according to officials from the Bureau of Reclamation and Northern Water. That’s partially because the structures underwent an $85 million renovation in the early 2000s. The modernization project included stripping the dams’ faces and adding a roughly 16-foot-thick filter of sand and gravel. Each of the dams was also bolstered for extra strength.

The lower risk here is also a question of magnitude, said Northern Water spokesman Brian Werner, who noted that the amount of water released through the Oroville Dam in 24 hours is more than Horsetooth Reservoir could hold at full capacity.

Perhaps most importantly, Horsetooth Reservoir’s relationship to its dams and water sources is different from Lake Oroville’s relationship with the Oroville Dam and the Feather River, which the dam impounds to form the lake. No river runs into Horsetooth Reservoir; gravity transports water there from other reservoirs in the Colorado-Big Thompson Project.

The Bureau of Reclamation in June 2016 finished a comprehensive review of Horsetooth Reservoir’s dams, which include the Horsetooth, Dixon Canyon, Soldier Canyon and Spring Canyon dams. All passed inspection.

Larimer County is home to 136 of Colorado’s 1,737 dams, according to 2013 data from the National Inventory of Dams. Twelve of those dams are very large…

Each of Larimer County’s high-volume dams received a satisfactory inspection rating at its most recent inspection, and none is used for flood control. All have emergency action plans, which include critical information like emergency contacts, details about the dam and an inundation map that shows where flooding will occur at different water levels…

Of Colorado’s 1,737 dams, about 25 percent, or 425, are considered “high hazard,” meaning one or more people are likely to die if the dam fails. About 96 percent of those dams have emergency action plans, significantly higher than the national rate of 69 percent.

An additional 19 percent of Colorado dams are considered a “significant hazard,” which means their failure would result in possible loss of human life and likely significant property or environmental destruction. About 92 percent of those dams have emergency action plans.

Inspection of Colorado dams falls to two agencies. The state’s dam safety division evaluates dams owned locally or by private and state agencies, and the Bureau of Reclamation monitors federally owned dams.

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