Residents along Colorado’s northern Front Range were still battling at mid-day Friday the effects of what state officials are calling “historically significant” rainfall and “biblical floods” along the foothills and across the Denver metro area.

Photo courtesy of CDOT
The heavy rains pushed rivers and streams above their historic flood levels and washed out highways, like State Highway 72 in Coal Creek Canyon west of Denver.
Photo courtesy of CDOT
Highway 34 in the Big Thompson Canyon west of Loveland, Colo., will be closed "indefinitely."

Some communities, including Boulder and those along the I-25 corridor north to Fort Collins, have received 12-15 in. of rain since the storm intensified on Tuesday night—nearly half of the average annual precipitation for the region. That is the equivalent of snowmelt from 9.5 ft of snow.

At least three people have died in storm-related accidents as of Thursday night, and thousands of people have been evacuated from their homes in Boulder, Estes Park, Commerce City, Longmont and other cities situated near the region’s swollen rivers and streams. Many area schools and businesses were closed on Thursday and Friday and officials asked drivers to stay off the roads.

As of early Friday afternoon, the Colorado Dept. of Transportation had closed portions of more than 35 major highways, including Interstate 25 north from Fort Collins into Wyoming and I-70 west of Denver due to mudslides. Cities and counties have closed hundreds of roads, bridges and side streets due to flooding.

Colorado Gov. John Hickenlooper declared a state of emergency and ordered the Colorado National Guard to help stranded residents and motorists. The Obama administration has authorized federal disaster funds to help with recovery and cleanup.

Officials say it is too early to offer damage assessments because they still can’t get into many of the hardest-hit areas. The town of Lyons, north of Boulder, is cut off on all sides by rising waters and flooded highways.

“We do not have any [damage] estimates right now and probably won’t for a few days,” says Mindy Crane, deputy director of communications for the Colorado Dept. of Transportation. “There are many areas we haven’t been able to fully assess the damage or even access.” Crane says that the agency is focusing nearly all its efforts on removing debris and reopening roads. Several highways leading into the foothills have been washed out and will be closed “indefinitely,” including Highway 72 through Coal Creek Canyon and Highway 119 west of Boulder.

Tony Milo, executive director of the Colorado Contractors Association, the state’s heavy-highway arm of the Associated General Contractors of America, says, “It's all very early but we are hearing $50 million-$100 million just in CDOT repairs that will be needed, and there will be more at the local level.”

Floods worsened along Boulder Creek and the Big Thompson River on Thursday night. The National Weather Service warned residents late Thursday that “a wall of water” was headed toward Boulder. The University of Colorado Boulder campus cancelled classes on Thursday and Friday and there were unconfirmed reports that 30% to 40% of CU campus buildings may have been damaged by the storm.

Boulder County officials report that water flow in Boulder Creek reached more than 4,500 cfs, double its peak flows over the past 25 years. All rivers and creeks in the area are reported to be at or above historic flood levels.

At least six dams along the Front Range have already collapsed and water has overflowed more than a dozen others, according to officials from the Division of Water Resources. Several more dams in Larimer County, near the Wyoming border, are in danger of collapsing. Many spillways have been activated, aggravating downstream floods. Some municipal water-treatment plants have scaled back operations because of rising floodwaters.

The storm that caused the heavy rains was the result of a seasonal monsoon flow north from the Gulf of Mexico that collided with a cold front moving down from Canada. The weather system has been stalled over the Front Range since Monday, creating what local forecasters are calling “100-year-or-worse floods.” Scattered showers with some pockets of heavier rain are expected through the weekend.