Flood risk not easily assessed
Seasonal weather proves more influential than thickness of winter snowpack
April 15, 2006
Steamboat Springs — The 432 inches of snow that fell on Mount Werner this winter have to go somewhere.
But those concerned about spring flooding don’t need to panic yet. Officials say snowpack depth isn’t the biggest factor that affects flooding.
“Above-average snowpack doesn’t necessarily mean major flooding,” said Brian Avery, a National Weather Service hydrologist.
Flooding is more dependent on the weather, said Chuck Vale, Routt County’s director of emergency management.
The two ingredients for high water or flooding are rapid snowmelt and rain, Vale said, which cannot be accurately predicted.
Last week’s high temperatures caused snow to melt earlier than usual, which could ease flooding in late May and early June, when the Yampa and Elk rivers usually reach their peak flows.
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However, the Yampa and Elk rivers roared at the end of last week with streamflows that quadrupled rates historically experienced at that time. And there are indications that the high water levels are not the result of high-altitude snowmelt but rather low- and mid-elevation snowmelt resulting from this winter’s abundant snows.
That could mean a prolonged period of high water levels and flood potential.
The lowest flood potential exists when spring weather brings mild temperatures during the day and below-freezing temperatures at night, said Jim Weber, Steamboat’s public works director. In those conditions, snow melts slowly but not continuously throughout the day.
When snow melts throughout the day and night, water channels become overwhelmed, Weber said. That’s when creeks and rivers crest their banks.
Although weather is the biggest factor influencing spring flood potential, residents of Routt County still should expect the winter’s abundant snowfall to add to the risk, Vale said.
“Because of the slightly higher-than-normal snowpack, we can probably assume that some of the tributaries to the Yampa and the Elk rivers will get out of their banks,” Vale said, adding that he expects the Elk River to flood.
Avery said that because the Yampa River is fairly shallow, it also is likely to crest its banks.
“People should expect some flooding to some degree,” he said.
In anticipation of that flooding, Avery and Vale said people who live in floodplains should get flood insurance. Because flood insurance does not take effect until 30 days after the policy is purchased, it’s important that residents buy insurance as soon as possible, they said.
All residents should stay away from rivers and creeks that are running high, Vale said.
“Keep children and yourself away,” he said, adding that tubing the Yampa River usually is not safe until June.
Avery said tubing early in the spring is dangerous because the water is moving fast and the snowpack-fed water is very cold. And, he said, dangerous debris could be submerged below sight.
Officials recommend that people who see debris in high water should call the public works department. Debris, including tree branches, can contribute to flooding.
The most recent long-term forecast predicts above-average temperatures and minimal precipitation through May, Avery said. But that prediction doesn’t rule out a hot or dry period.
“That’s the problem with forecast modeling,” Avery said. “It assumes current conditions and normal weather throughout the period. That can go out the window.”
Vale said that it’s impossible to tell exactly what’s going to happen this spring.
“All this is contingent upon Mother Nature,” Vale said.