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Exercise considers ‘worst-case scenario’ of Granby Dam failure

by Tonya Bina
Sky-Hi Daily News
The Granby Dam took nine years to build and was completed in 1950. It's constructed of compacted earthfill, 298 feet high, with a crest length of 861 feet. There are 12,722 feet of auxiliary dikes, that, with the dam, create a reservoir of about 539,800 acre-feet of water. (Photo by Tonya Bina)
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What if 361,000 acre feet of water, the amount that is in the reservoir today, were to breach the Granby Dam and spill into the river valley?

Area emergency responders took part in a table-top exercise earlier this month to review and revise the play book of what to do if this “worst-case scenario” were to happen.

“It’s important that the local, county, state, and federal agencies are working together to coordinate and be prepared in case something this unlikely does happen,” said Bureau of Reclamation spokesperson Kara Lamb.

The formal exercise, conducted every three years, is part of the Safety of Dams program through the Bureau, which owns the system of dams and dikes that make up the Colorado Big Thompson Project. The table-top exercise is followed up with a functional exercise, to take place next year, during which emergency officials act out the communication in the plan.

The exercise took place on Nov. 2 in Granby, focusing on Granby, Willow Creek and Shadow Mountain dams.

There are no current issues with the dams, Lamb stressed, and there hasn’t been since they were constructed.

Nevertheless, the exercises are part of an effort to be prepared for a wide realm of circumstances that could happen, she said.

County emergency officials were treated to a scenario that, for people like Granby Mayor Ted Wang, were an eye-opener for what could happen if the Granby Dam were to break.

The worst-case-scenario simulation estimated that if seepage were identified at 7 a.m., and the dam were to completely fail by midnight, the flats west of Granby would end up with 30 feet of water on the ground and Hot Sulphur springs would experience water 50 feet above ground. The water would follow the flow corridor of the Colorado River and spill out into low-lying areas, submerging the future community Orvis Shorefox and Granby’s “hotel row” as well as Hot Sulphur Springs.

Mayor Wang noted at the exercise that the Orvis development at the west-end of Granby could have an estimated population of 1,800 residents.

Warnings about any possible dam failure would take place before an actual break and every effort would be made to warn the communities, said Grand County Sheriff Rod Johnson. The Grand County Sheriff’s office would be in charge of coordinating the effort to get people to safety.

The recent emergency practice exercises should not cause alarm, officials reiterated.

Lamb encourages area residents to keep faith in the dam and its operators. Earthen dams are extremely stable because they are so thick, and it’s “very unlikely you’d see anything like this happen,” she said.

With the Bureau’s 375 dams and dikes across the western United States, some more than 100 years old, the Bureau has had one failure. On June 5, 1976, the Teton Dam in Idaho, designed by the U.S. Bureau of Reclamation, failed just as it was being completed and filled for the first time. The collapse resulted in the death of 11 people and 13,000 head of cattle, and total damage estimates have ranged up to $2 billion.

The dam was never rebuilt.

“Because of that, the whole Safety of Dams was created,” Lamb said.

The program is funded separately from the agency due to its importance; that way, budget cutbacks cannot affect it, she said.

At full capacity, the Granby Reservoir can hold 540,000 acre-feet of water, which puts water elevation at 8,280 feet.

On this November day, the water sits at an elevation of 8,253 feet.

-Tonya Bina can be reached at 887-3334 ext 19603 or e-mail tbina@grandcountynews.com.


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