1,500 homes destroyed in Colorado floods

Daily News Article   —   Posted on September 17, 2013

(by Keith Coffman, Reuters) DENVER – Seven people were confirmed dead and at least 1,500 homes destroyed in Colorado after a week of rare, torrential rains along the eastern slopes of the Rockies, and helicopter search-and-rescue flights resumed on Monday in flood-stricken areas.

Much of the evacuation effort was focused on remote foothill and canyon communities of Larimer and Boulder counties in north-central Colorado, where 1,000 residents remained stranded due to washed-out roads, bridges and communication lines, the county sheriff’s office said.

Drizzle and patchy morning fog that had hampered airborne emergency operations lifted by Monday afternoon, allowing National Guard helicopters to return to the skies to help ground teams find trapped flood victims and carry them to safety.

Ranchers were advised to move livestock away from rain-swollen streams as floodwaters spread further east onto the prairie, and authorities warned residents to be on the lookout for rattlesnakes that might be moving to higher ground.

Larimer and Boulder counties bore the brunt of flash floods first unleashed last week by heavy rains that started last Monday (Sept. 9) and drenched Colorado’s biggest urban centers along a 130-mile stretch in the Front Range of the Rockies.

At the peak of the disaster, the heaviest deluge to hit the region in four decades, floodwaters streamed down rain-saturated mountainsides northwest of Denver and spilled through canyons funneling the runoff into populated areas below.

The flooding progressed downstream and spread onto the prairie on Friday. During the weekend, waters topped the banks of the South Platte River and inundated farmland as high water rolled eastward in the direction of Nebraska.

State officials issued flood warnings to Nebraska residents along the South Platte. State emergency management spokeswoman Jodie Fawl said they began putting sandbags inside culverts beside a Union Pacific Railroad line in the town of Big Springs to prevent a wash-out of the tracks there.

The Colorado Office of Emergency Management issued a statement on the disaster, putting the official death toll at seven, up from five over the weekend, but a breakdown of the fatalities was not immediately available.

Separately, two women, aged 60 and 80, remained missing and presumed dead after their homes were washed away by flash flooding in the Big Thompson Canyon area, Larimer County sheriff’s spokeswoman Jennifer Hillmann said. But she said local authorities were still not counting those two women as confirmed dead because their bodies had not been recovered.

Nearly 400 other people remain unaccounted for in Larimer County, with many believed to be still stranded in remote areas cut off by floodwaters and left without telephone, cell phone or Internet service, she said.

An estimated 1,500 homes have been destroyed and 4,500 more damaged in Larimer County alone, Hillmann said. In addition, 200 businesses have been lost and 500 damaged, she said, citing preliminary assessments by the county.

As the weather began to clear Sunday night and Monday, rescue workers fanned out across a flood zone encompassing an area nearly the size of Delaware.

“They’ll take advantage of the weather today and help out everyone they can,” said Micki Trost, a spokeswoman for the state Office of Emergency Management. “We hope that those weather forecasts stay in our favor.”

The air rescue operations were the largest in the United States since flooding in the aftermath of Hurricane Katrina devastated New Orleans in 2005, National Guard officials said.

Bryon Louis of the National Weather Service office in Boulder said some areas had been soaked by as much as 16 inches of rain in just three days, the average for an entire year in the semi-arid region. …

U.S. Army and National Guard troops have rescued 1,750 people cut off by washed-out roads in the mountain canyons of Boulder and Larimer counties, Army spokesman Major Earl Brown said in a statement.

State officials would be unable to assess the overall damage until rescue efforts were complete and the floodwaters had receded, Trost said.

The prolonged showers were caused by an atmospheric low-pressure system that stalled over Nevada and western Utah, drawing extremely moist air out of Mexico and streaming it north into the southern Rockies, meteorologists said.

The last multi-day rainfall event to spawn widespread flooding in Colorado’s Front Range occurred in 1969. But a single-night deluge from a 1976 thunderstorm triggered a flash flood that killed more than 140 people in Big Thompson Canyon.

(Reporting by Keith Coffman; Writing by Steve Gorman; Additional reporting by Tom Brown; Editing by Dan Whitcomb, Richard Chang and Ken Wills)

Reprinted here for educational purposes only. May not be reproduced on other websites without permission from Thomson Reuters. Visit the website at Reuters.com. 

Background

What caused deadly Colorado floods?

Boulder picked up almost nine times its average September monthly rainfall in about four days.

Colorado is no stranger to devastating and deadly flash floods, due to a lethal combination of geography and meteorology. When unusually heavy rain falls across the region, narrow canyons and steep mountains help funnel raging torrents of water down into the heavily populated foothills to the west and north of Denver.

One of them, the notorious "Big Thompson" flash flood of July 1976, killed at least 144 people north of Boulder. It caused "the worst natural disaster, in terms of documented lives lost, in Colorado state history," according to Boulder's Flood Safety Education Project website.

Boulder, specifically, is considered to be Colorado's "most at risk" city in terms of potential flood damage, notes Weather Underground weather historian Christopher Burt. This is because it rests against the mouth of a canyon (the Boulder Canyon) from which a creek (the Boulder Creek) bisects the heart of the town.

This week's rains and floods in Colorado were the result of a strong, slow-moving storm at upper levels of the atmosphere located to the west of the state, according to meteorologist Jeff Masters with the Weather Underground. The storm got trapped to the south of an unusually strong ridge of high pressure parked over Western Canada, he says.

The circulation around the storm tapped a plume of extremely moist, monsoonal air from Mexico that pushed up against the mountains and fell as rain on the already saturated ground, soaked from rain earlier in the week, Masters adds.

How much rain? From the afternoon of Sept. 9 through midday on Sept. 13, 14.62 inches of rain fell in Boulder. Average September rainfall in Boulder is only 1.63 inches, according to Weather Channel meteorologist Jon Erdman, adding that Boulder picked up almost nine times its average September monthly rainfall in almost four days.

Finally, winds 15,000 feet above the ground were generally blowing from southeast to northwest and were light, Erdman says. This allowed the rain and thunderstorms to linger over the foothills and Front Range urban corridor.

"This is a classic scenario for major flooding in northern Colorado," he says. (from usatoday)

More information about the damage:

• Area affected: 15 counties, inundating at least 2,380 square miles - Of these counties, Larimer and Boulder counties appear to have been the worst-hit.
• About 600 Colorado National Guard and active-duty U.S. Army personnel were assisting local emergency officials with relief efforts, officials said. Federal rescuers had saved 2,100 stranded residents along with 500 pets by air and more by ground over the course of the disaster, guard spokeswoman Theiral said.
• Number of people evacuated: 11,700 - This is another number from state officials that may rise as emergency officials and Colorado National Guard and U.S. Army personnel continue to rescue more stranded residents.
•  As of Sunday: 1,872 evacuees staying in 26 shelters across the state.
• Number of structures destroyed: 1,502
• Number of structures damaged: 17,494
• Number of bridges destroyed: 30 - That figure is from the Colorado Department of Transportation, with officials adding that another 20 bridges have been seriously damaged. Joshua Laipply, a CDOT bridge engineer, told the Post that the count may continue to rise.
• Due to widespread road and bridge damage and destruction, evacuations are more dependent on helicopters - that means rescues are more at the mercy of the weather: When inclement weather continued on Sunday (Sept. 15) 20 military helicopters supporting the relief effort were largely grounded, Colorado National Guard spokeswoman Cheresa Theiral said.
• State transportation officials urged travelers to avoid all unnecessary travel on highways and interstates in Boulder, Larimer, Jefferson and Clear Creek counties because the roads may have been damaged or destroyed.
• 100 miles of roads have been damaged or destroyed.