LYONS, Colo. (AP) — The pristine snow piled high in the northern Colorado mountains is beginning to melt, and officials worry that under the wrong conditions, it could unleash another ugly torrent through towns and farms still scarred by last autumn's floods.
After a wintry Mother's Day storm, the snowpack is nearly 150 percent of the mid-May average on the slopes that feed the South Platte River, whose tributaries did some of the worst damage in the September floods.
A heat wave or rainstorm could suddenly accelerate the runoff and send water gushing into flood-damaged streambeds that might not be able to contain it, experts say.
So far, the long-term weather outlook isn't definitive.
"Fifty-fifty, could be bad, could be good," said Kevin Klein, director of the Colorado Division of Homeland Security and Emergency Management, which began planning for the runoff almost immediately after September's flood.
Colorado's spring runoff normally doesn't cause floods, even though most of the state's surface water is collected in a 2-month frenzy of melting snow, said Nolan Doesken, the state climatologist.
But some streambeds in northern Colorado are loaded with tons of sand and gravel swept down by the September floods, so they hold less water and are more likely to overflow, said Treste Huse, a National Weather Service hydrologist.
There's also some evidence the water table remains high and the ground is still saturated in areas that flooded, experts said. That could send runoff rushing down canyons instead of soaking into the soil, and it could make hillsides more susceptible to landslides and rock fall.
The September floods killed nine people, and a 10th was killed during recovery operations. A storm backed into the mountains from the east and sat for days, pouring out rain that overwhelmed rivers far out on to the state's eastern plains. Nearly 2,000 homes were damaged or destroyed; total damage was estimated at $2 billion.
It was described as a once-a-century flood or even a once-a-millennium flood, but Klein said researchers are still unsure about where it fits in climate history.
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