Will big snowpack bring floods to Colorado Front Range?

Planners gird for more woes after major snows.

 

Dan Barber, the deputy director of Boulder County’s office of emergency management, likes to think in terms of stream flow.

At the height of the Front Range flood in September 2013, Boulder Creek was roaring through the canyon at a flow rate of 5,500 cubic feet per second. To Barber, that’s a more interesting number than the 25-year or 100-year flood that got bandied about.

With that much water moving through the mountains, sediment, trees, boards – all manner of debris – shot through the drainages of the Front Range, particularly in Boulder and Larimer counties. Some of the creeks have since been cleared out, but many of the roads that were destroyed by the flooding have only received short-term repairs.

This year’s snowpack has been a mixed bag across the West. Some places remain very dry, but in some, like northern Colorado, late season storms bolstered the snowpack. And the later the snowpack stays without melting out, the more worried water managers and other weather watchers get.

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Colorado, Rio Grande, and Arkansas River Basins Mountain Snowpack as of May 1, 2014. Map of the Natural Resources Conservation Service.

So with temperatures warming and a hard rain coming down on the plains east of Boulder on Tuesday, Barber has been thinking of stream flow a lot lately.

“It’s an anxious time right now,” he told me on Thursday morning, as the flow of Boulder Creek crept toward 500 cubic feet per second. Barker Reservoir, a catchment below the nearby town of Nederland, was likely to spill its banks in the next few days, he said, pushing that flow rate up toward 700 (the rate at which Boulder bans river tubing).

And there’s even more water up there, locked in snow. Most of the mountains of northern Colorado still have major snowpack, upwards of 150 percent of normal, and spring temperatures are warming as we slide toward summer, lessening the chance of a gradual melt-out, Matthew Kelsch, a hydrometeorologist at the University Corporation for Atmospheric Research, said. “The bad news is, we’re already in the middle of May.”