CHERRY CREEK DAMNED? ‘High-risk’ Aurora dam receiving review

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AURORA | A few years down the road, Aurora could feasibly get slammed with one of those once-in-a-lifetime, Biblical-type rain storms.

And if it’s really, really big — like the sort of storm that makes the days of record rain that sparked flooding in fall 2013 look like a brief afternoon sprinkling — the way Cherry Creek Reservoir diverts that water could be a lot different than it would be if that storm happened today.

It’s not that the Cherry Creek Dam, which towers more than 140 feet over southwest Aurora, is at risk of overtopping — far from it, officials say.

“The dam, structurally, is in very good condition,” said Steve Butler, project engineer for the Cherry Creek Dam Safety Modification Study.

But the dam is deemed “high risk” because of where it sits — smack in the middle of a bustling metro area with more than 300,000 homes sitting just downstream.

Among the dams the Army Corps of Engineer manages, Butler said Cherry Creek is probably in the top 5 percent in terms of the potential consequences should it ever fail.

Butler said that with the sort of damage any overtopping of the dam could cause, officials have to be on the lookout for the best ways to deal with those incredibly rare weather events.

Officials from the Corps are already working on ways to tweak how the reservoir dumps excess water, including allowing more water from the reservoir to flow into Cherry Creek, and later the South Platte River. They’re also crafting plans to beef up the amount of water the reservoir’s spillway can handle.

And they could pursue another major change, too: raising the dam by as much as six feet.

Butler said the water control plans that would allow more water from the reservoir into the creek and improve the spillway are already set to go before Army Corps of Engineer officials for approval early next year. Engineers are still considering whether to pursue raising the dam.

The Corps of Engineers earlier this month extended to Dec. 16 the public comment period for people to chime in on those proposals.

“Extreme rainfall events occur, which is why we must have plans in place to address them,” Kellie Bergman, chief of water management for Corps of Engineer’s Omaha District, said in a statement.

But, Bergman noted, the reservoir’s record elevation is still a full 25 feet lower than the level that would trigger the new releases.

Butler said that if the reservoir were to be raised, it would be a pretty substantial construction project and likely take a couple years to complete.

And, he said, any raise to the reservoir would have other consequences. While it would decrease the risk of overtopping, raising the dam would also mean the inundation area on the other side of the dam — the neighborhoods to the south that could be impacted should the reservoir swell — would be expanded.

The Corps of Engineers has been working in recent months with nearby communities to get their input on any potential changes to the dam.

Arapahoe County officials said they are reviewing the plans this month.