Flash Flooding Causes Damage in Northern Colorado

September 13, 2013

Three days of intense rainfall in many areas of Colorado has resulted in severe, widespread flooding and collapsed homes, according to Boston-based catastrophe modeler Air Worldwide.

The greatest threat is to cities along the Front Range, including the city of Boulder and parts of the Denver metropolitan area, AIR reported.

Flash flooding in Colorado has left three people dead and is keeping search and rescue teams from reaching stranded residents.

The National Weather Service has warned of an “extremely dangerous and life-threatening situation” throughout the region. Collapsed homes and mudslides have been reported in the mountainous region.

Boulder Office of Emergency Management says many roads are impassable.

Essentially all water bodies in these areas including ditches, canals, and streams are at capacity with many of them at flood level, according to AIR.

“Severe flooding began during the evening of Sept. 11, when several areas received up to 2 inches of rainfall per hour,” Yucheng Song, senior scientist for AIR, said in a statement. “In Erie, which is located in Boulder County, the Erie Parkway was submerged under a foot of water. By the morning of Sept. 12, a flash flood warning had been issued for the areas affected by the Waldo Canyon wildfire last year, where the lack of foliage within the burn scar has increased the risk of excess runoff.”

According to the National Weather Service, a 20-foot wall of water was reported in a canyon north of Boulder.

The government buildings in the city of Boulder, as well as the University of Colorado and Naropa University are closed, and between 400 and 500 students and faculty from the University of Colorado have been evacuated from on-campus housing and several homes in the University Hill area of Boulder have reported flooding, according to AIR.

According to AIR, this region often experiences heavy precipitation this time of year, but it has also been an unusually wet summer, with over 10 inches of rain inundating parts of Colorado during July and August.

“Currently, a surge of moist air that originated in the Gulf of Mexico has combined with a low-pressure system over Utah and a cold front,” Song said. “The area’s mountainous topography causes the air to cool as it moves upslope, producing more precipitation. This upslope flow will continue over the next few days due to a high pressure system to the east that will keep the system virtually stationary over the next few days.”

According to AIR, Colorado has a long history of flood events and flood mitigation efforts. In Boulder County, these include codes and ordinances that prohibit, or limit, building in floodplain areas, and channelization and detention ponds have been built in the county and several high-risk buildings located in floodplains have been removed, AIR stated.

Yet, despite these efforts the area still has vulnerable structures. Roughly seven-in-10 of the residential construction is wood, with an estimated 40 percent having basements, according to AIR. The presence of a basement increases the risk for contents and building damage.

According to AIR, commercial business can add flood as an endorsement to their property policy, although it is often subject to sublimits. The experience of Hurricane Katrina revealed that commercial insurers did not always have good information about their exposure to flood and indeed estimates of total industry-wide insured flood values remain hard to obtain.

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