It’s no secret that Boulder, Colo., was likely to experience a major flash flood at some point. Located at the base of the Rocky Mountains, the city rests up against a canyon from which a creek runs through Boulder, nearly cutting it in half. The Boulder Creek has been called the No. 1 flash flood risk in Colorado, and 15 creeks with flood plains affect more than 15 percent of the city. Cementing the likelihood of a major event, in 2004, the University of Colorado at Boulder’s Natural Hazards Center listed a flash flood in Boulder as one of six “disasters waiting to happen” in the U.S.
And though few may have expected what the National Weather Service described as “biblical rainfall amounts” in the second week of September, Boulder was prepared for the flash flooding that followed the torrential rainfall — the city and county’s engineers, scientists and emergency managers had been preparing for decades.
Mitigation and preparedness efforts can be traced back to a series of events: The flood of 1969 led the city to adopt flood plain regulations after four days of rainfall drenched the area with more than nine inches of water. Then in 1976, the Big Thompson flood served as a lesson for all Colorado communities that are at risk of flash flooding. Over a four-hour period, up to 12 inches of rain came down in the mountains near Estes Park, causing the state’s deadliest flash flood — 143 people were killed and another 150 injured. And in 2010, to the west of Boulder, the Fourmile Canyon fire burned 169 homes and 6,181 acres, leaving a burn scar that greatly increased the likelihood of flash flooding because of a lack of plants and undergrowth to trap moisture. These natural disasters created a more prepared city and county, and while four lives were lost in Boulder during the 2013 flooding, the lessons and initiatives from past disasters proved immeasurably valuable.
“Since the Fourmile fire, a tremendous amount of community education and also government preparedness went into flooding because the burn scar created a very unique flash flooding risk that normally isn’t there,” said Mike Chard, director of the Boulder Office of Emergency Management.
As the emergency situation played out, so did the city and county’s strategies. Here’s a look at how Boulder weathered the storm.
Internal policies have shifted the city and county Emergency Management Office from a planning and preparatory function into also a predictive function, Chard said, so when there’s a possibility for an intense storm, the emergency management staff follows the severe weather protocol and mans the EOC to maintain situational awareness. This allows the office to be prepared to supply first responders with vital information in case the situation gets to the point where they need to step in and make public safety-related decisions like whether to evacuate an area.
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This is key because one of the most dangerous aspects of a flash flood is that it doesn’t allow for much lead time. “We have to shift operations from identifying and gathering information to making decisions about public safety all within about an hour,” Chard said. “If peak flow is achieved in about 20 to 30 minutes, flooding will start about 20 minutes after that. So we have a very narrow window of time.”
And that’s what was done on Sept. 11. The severe weather protocol was implemented at 11 a.m. and by 4:00, “we knew we were in trouble,” Chard said. The more than nine inches of rain that fell on Sept. 12 was a record for a single day; instead of issuing evacuation orders, alerts told residents to climb to safety.
Numerous alerting methods were used to get the message out — sirens blared; the Everbridge mass notification system sent texts, calls and emails to residents; the Emergency Alert System and Wireless Emergency Alerts were used; and messages were distributed via social media. In this case, the flooding was widespread so messaging wasn’t needed for just select groups of at-risk residents. But if the flooding had been threatening specific areas, Boulder was prepared with hazard-specific alerting polygons. Chard said that in many cases, people draw a large polygon on a map and alert people within that polygon, into the thousands in some cases, and getting the message to that large of an audience can cause a delay in the system.