This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
LONGMONT, Colo.—Three days of soaking rain in Colorado have unleashed damaging floods in and around Denver, Boulder and Colorado Springs and isolated some towns in the foothills of the Rockies. An additional several inches of rain overnight swelled mountain creeks sending runoff from the mountains and into the populated areas downhill. Along the Front Range, from Colorado Springs north to Fort Collins, thousands of residents are being evacuated. Three people have been reported dead as a result of the disaster, and officials expect to find more as floodwaters continue to intensify.
In the past few days, Boulder received a record-breaking 9.6 inches of rain as of Thursday afternoon, and it is still falling—an unusual sight for an area that boasts 350 days of sunshine a year. "It's a staggering amount of precipitation," Gov. John Hickenlooper told a local radio station. The rain has made this month the wettest in Boulder history, National Ocean and Atmospheric Administration scientist John Brown told The Washington Post.
One bystander observing the St. Vrain River flooding over its banks this morning in Longmont, a town of about 87,700 located 15 miles northeast of Boulder, noted he had never seen the water come close to these levels in his 51 years living in the area. Runners, accustomed to uninterrupted miles of trail far above the St. Vrain River and Boulder Creek, found only short stretches this morning that were still above water. Water from the normally tame St. Vrain, which flows through Longmont as well as many surrounding communities, topped nearly all of the city's major bridges by midday Thursday, damaging homes and stranding motorists as it bisected the city.
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Boulder Creek, which runs through the center of the university town, was above flood stage. The city has not experienced a so-called 100-year flood since 1894, and a 2004 report from the University of Colorado, Boulder, ranked its home town as a flooding disaster waiting to happen, noted the Boulder Daily Camera. The University of Colorado, local school districts and businesses closed for the day. At least a quarter of University of Colorado's Boulder campus buildings were affected by flood waters as of midday Thursday, including some of it laboratory structures and faculty and student housing. Mountain communities and neighborhoods in Boulder, Longmont and elsewhere were being evacuated today, and power outages were ongoing throughout the region.
Suburbs of Denver have also been affected, and flooding has closed portions of the major thoroughfare I-70 near Aurora. Firefighters rescued three drivers from cars near suburbs Lafayette and Broomfield after a road collapsed, according to the Denver Post.
The mountain foothills town of Lyons, north of Boulder and a destination for bluegrass music festivals, is now cut off after a collapse of Highway 36. Local officials are reporting that it is experiencing a 500-year flood and that 200 residents had already arrived at an evacuation shelter, according to the Longmont Times-Call.
Fires in the mountains in the past few years have left large burn areas in the canyons that are now at higher risk for flash-flooding. Such terrain results in more runoff, increasing flood and landslide hazards downhill. Fourmile Canyon, which burned in 2010 and is just northwest of Boulder, has already lost multiple structures due to flooding. Mudslides and water are hampering ongoing rescue efforts there and in other foothill communities.
Flash flooding has also occurred elsewhere in the state, claiming at least one victim in Colorado Springs, and inundating the downtown of Estes Park, the gateway to Rocky Mountain National Park.
Emergency disaster declarations have been made in Boulder and Longmont, and the National Guard has been called in to assist with rescue efforts, although fog has kept many of the requested helicopters grounded. Boulder area updates are available from their Office of Emergency Management.
Floodwaters were expected to crest between 3 p.m. and 4 p.m. Mountain Time, but flash flood warnings remain in effect until Friday morning. "The event is far from over," Boulder Sheriff Joe Pelle told the Denver Post. Rain is forecast to continue in the area through Saturday.