‘Catastrophic flooding’ in Summit County unlikely, but avalanche debris adds uncertainty to runoff season | SummitDaily.com

‘Catastrophic flooding’ in Summit County unlikely, but avalanche debris adds uncertainty to runoff season

The Blue River flows Monday, April 29, in Silverthorne.
Hugh Carey / hcarey@summitdaily.com

A blustery winter lifted area snowpack well above normal levels. However, it also produced avalanches of historic proportions that tumbled down into the valleys, bringing with them massive deposits of debris.

And now comes runoff season. What could go wrong?

Overall, Summit County officials said they aren’t anticipating major issues. Despite that, they’re still preparing themselves for anything.

“It’s tough because every year the primary tactic is wait and see,” said Brian Bovaird, Summit County’s director of emergency management. “This year we do have more snowpack, but if it’s a gradual runoff and more gradual rains, the snowpack isn’t concerning.”

Treste Huse, a hydrologist based out of the National Weather Service office in Boulder, said that despite a relatively dry April, Summit County’s snowpack is still well above normal at about 131% of average.

Regardless, Huse noted that Summit’s runoff — in part due to the Green Mountain and Dillon reservoirs — is typically “well behaved.”

“There might be minor flooding, but generally we don’t have issues where we enter a flood stage,” said Huse.

Additionally, because of drought conditions last year there’s lower than normal reservoir levels heading into the spring runoff. Todd Harman, a representative with Denver Water, said that while the Dillon Reservoir is typically about 85% full at this time of year, it’s currently only at about 70%, meaning there’s additional space to help capture excess runoff.

WEATHER DEPENDENT

But unfavorable weather conditions can still be a problem. Huse said that temperature and rain are the major deciding factors in determining how fast runoff comes off of the peaks. In an ideal scenario, Summit County would enjoy warm days that melt the snow and ice, and below freezing temperatures at night to slow the process. Huse said that higher temperatures at night would create isothermal conditions wherein the snowpack is largely water, which could create rapid melting and increases in stream flow.

Natalie Sullivan, a forecaster at the National Weather Service, said that Summit County should see snow continue to pile onto the slopes over the next week, with up to 7 inches by Tuesday morning, up to 4 new inches Tuesday night and maybe more on Sunday.

Sullivan also said that this year’s temperatures are consistent with previous years, with highs in the mid-30s to mid-40s, and nighttime lows in the mid-20s to mid-teens. Though, with Summit County’s peak runoff season typically running from mid-May to early June, it still remains to be seen how well the weather will cooperate.

AVY DEBRIS

The bigger issue is obstructions in the waterways that could potentially spur flooding. Following a historic avalanche season in Summit County and around the state, a considerable amount of debris crashed into the Tenmile Creek, creating concerns about natural dams and sudden flooding.

“Out of the ordinary this year is all of the debris from the avalanches in Tenmile Creek,” said Bovaird. “It’s not just trees, but boulders, debris and dirt that got into the waterways there. There are some concerns about debris washing down the creek towards Frisco. But that’s not as concerning as if a lot of that debris blocks up the waterway, creates a dam, blocks the water and breaks loose.”

The result downstream would likely be flooding in Frisco. Bovaird said that any operations to try and remove or mitigate the debris in the water is unrealistic, and that all they could really do is monitor the situation and be prepared if major buildups do occur. Even if the debris does create issues, Bovaird said that his office doesn’t expect “catastrophic” flooding even if the worst comes to pass.

Though, even minor flooding can be very dangerous. Bovaird said it takes just 6 inches of running water to sweep a person away, and 12 inches to wash away a vehicle.

While experts with the emergency managers office and the U.S. Forest Service maintain they don’t believe residents in the area will require any extra safety precautions than usual this season, there’s still plenty of resources available for concerned individuals.

Each year the county publishes a flood preparedness guide with helpful information on their website. Denver Water also offers regular updates via e-newsletters and their website on water levels, stream flows and releases at the reservoir. The county and the towns within offer free sand and sandbags for residents and property owners.

Finally, Bovaird recommended that residents take the time to sign up for Summit County Alert, where county officials can send out warnings about potential flooding in certain areas.

“We’re not anticipating any catastrophic flooding,” said Bovaird. “But we could see some things we usually don’t. The biggest thing is just safety. It’s important for people to just be aware of those hazards, and keep themselves safe.”


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