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How Boulder, Colo., Prepared for ‘Biblical’ Rainfall

Torrential rain and flash flooding tested Boulder’s preparedness and mitigation initiatives, but lessons from previous disasters kept the community afloat.

Boulder flood 2013
Photo courtesy of Staff Sgt. Wallace Bonner/U.S. Army


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.



Read about how the University of Colorado at Boulder relied on relationships and mitigation efforts during the 2013 flooding.

In early September, the National Weather Service told Boulder’s emergency managers that monsoon season was coming and how it could affect the area. Then the weather pattern developed and heavy saturation was headed for Colorado’s Front Range. “The scenario was set for the 11th with what the Weather Service says is our worst-case scenario, which is an upslope storm where it’s piling up against the mountains,” said Dan Barber, deputy director of Boulder’s Emergency Management Office.

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.

“We created polygons with residents that were specific to high flood-prone areas with crafted messaging that was unique to that area,” he said. “So the fire chief or sheriff could say, ‘Give me polygon 17 with message two,’ and the dispatcher would pull it up and off it would go.”

Aside from sending information out to residents, a new role in the EOC was created to provide situational awareness based on what people were posting online. The E-Sponder monitors, filters and disseminates social media information in Boulder’s EOC. “For example, college kids were playing in the water and we were able to see it happening online,” said Amy Danzl, an emergency management specialist with the office. “What was really good for us was we could see the levels of water immediately.” Watching social media posts about the flood also helped the EOC follow the public sentiment. Danzl said the same time the e-sponder observed that messages were becoming negative on Twitter and people were getting scared, the EOC received information that the situation was getting worse. “Knowing the tempo of the public gives us and our public information officers a better idea on how to respond and frame the message,” she said.

Building situational awareness using social media also helps to push information to first responders about what’s happening on the ground. They look for trends, Chard said, instead of responding to every post. He said the model is to triangulate data — if a topic is seen three or more times, they start to track and verify the information before moving forward on it.

Another tool aiding awareness is a network of rain and stream gauges that was installed by the Urban Drainage and Flood Control District, an independent agency that has been assisting Colorado local governments with drainage and flood control programs since 1969. The gauges feed real-time information to officials and also send an alarm if the water reaches predetermined levels. Chard said they read the rain gauges for homes that are at the  bottom of the canyons to help determine peak flow and if residents need to be warned about a possible flash flood.

“We also use the stream gauges to verify the flow that will be happening in the creek and then that is good information to give to our city of Boulder partners and stakeholders to say, ‘Here’s what we are predicting will come your way,’” he said.

The collaboration with the National Weather Service, Urban Drainage’s meteorological firm, and city and county hydrologists all create a coordinated and informed response. Another entity that plays into this is the Multi-Agency Coordination group. Composed of government, nonprofit and private organizations, Denzl said the group has been meeting for many years and the participants are depth trained to work in the EOC. The group is organized into sections, like infrastructure and community services, and its members were advised on Sept. 9 that because of the ground saturation and weather predictions to be available in case the situation escalated — they are the “foundation of the EOC,” according to the office’s website.

Another group that aids coordination was developed after the Fourmile Canyon Fire. The Intermountain Alliance ties together six mountain communities with the Boulder Emergency Management Office, and the planning effort for the past two years has been around an event that cuts the cities off from the plains where the resources are, said Chard. And that’s what happened during the September flooding. The town of Lyons was widely publicized for being cut off from outside aid after roads and highways were washed out. The same situation happened in Jamestown, and the mountain communities supported one another as they had been training to do. Chard said they were able to open shelters, deal with unmet needs and provide safe sites for people who were coming out of the valleys and to the high points.

The mountain community leaders also partnered with the Boulder County Amateur Radio Emergency Services, and 80 people have been trained in ham radio operation in the last two years. The flooding took out telephone poles but communication links remained between the ham radio operators and Boulder EOC.

“We were able to maintain effective communications back and forth from the hills to the valley, which was critical in being able to tell people what’s happening, what we can get you and find out what they needed,” Chard said. “We were able to air drop in resources and coordinate that with the people who were up there through ham radio — it was a pretty incredible coordination effort.”

Having a scalable logistics and resource mobilization system also proved to be key. Boulder Emergency Management was in the process of building the system before the 2010 Fourmile fire, and many lessons learned from that event helped improve processes, helping it to be able to scale to the level needed during the flooding. Denzl, the resource mobilization and logistics section chief, filled 422 orders, many of which requested multiple resources. The outside aid agencies were accustomed to working on large-scale events and were ordering hundreds of port-a-potties, thousands of pallets of water and even a circus tent (to be a briefing room for the incident management team).

“From a local level, our system has to be very scalable to order everything from ink pens for our EOC to multimillion dollar orders for equipment and staff,” Denzl said.

Within Boulder, a flood management program has been in place for more than 30 years, and since 1997, the city has spent about $45 million on mitigation projects, which include floodgates, underpasses and storm sewer improvements.

Going further back, flood plain regulations were adopted in response to the flood of 1969, said Katie Knapp, the city’s engineering project manager. In addition, Boulder joined the National Flood Insurance Program in 1978, and its regulations exceed the program’s minimum standards. The city requires, for example, that residential structures are elevated two feet above the base flood water elevation, whereas the national standard is to be at the base flood elevation.

Boulder also is a class six in the program’s Community Rating System, an incentive program that lowers flood insurance premiums. And those efforts seem to being paying off. “The city has more flood insurance policies than any other community in the state,” Knapp said, but she didn’t have exact numbers.

The area within the 100-year flood plain at the greatest risk for life and property damage was established as a high hazard zone. The city doesn’t allow any structures that are intended for human occupancy in that zone, and it looks to acquire property there when possible. The buildings are removed and overbank grading allows additional capacity for floodwaters, said Knapp.

Another mitigation project is a system of multiuse trails that run along the creek corridors kind of like a linear park area. Called the Greenways, the trail system allows the creeks area to have additional water capacity while also providing recreation areas, improving storm water drainage and protecting resources. Being multiuse allows for numerous funding opportunities, Knapp said; adding underpasses, for example, crosses into transportation, so multiple objectives can be met by each Greenways project.

Boulder’s combination of projects and initiatives through the decades proved invaluable to the city during the flooding. “You have many bridges and roadways that may have overtopped or were cut off at some point but are standing today because of those mitigation efforts,” Chard said. “The mitigation efforts were paramount to response and recovery.”

As the city and county move forward with recovery, lessons learned will continue to shape a better prepared community. As of press time, the Boulder Office of Emergency Management had not completed an after-action report, but “things went well for us,” said Chard. The office will examine the early warning systems, operational command structures, how the EOC interfaced, and the quality of communication and information sharing.

One issue that stuck out was the need for communities to have their own sheltering and unmet needs plan. During this event, the American Red Cross was strapped for resources and, along with other aid organizations, couldn’t get into the affected areas for a some time. “We have been working to build that into our response plan,” Chard said.

In addition, some of the stream and rain gauges were washed away. Barber said they will look into replacing them and determining if they need to be in different locations as well as the possibility of adding them farther up the canyons.

The city has been holding open houses in different neighborhoods to show residents the flood plain maps and identify where flooding occurred. At future meetings, Knapp would like to incorporate stations to provide people information on how they can protect their property as well as help them with personal emergency planning.

“In the past it was a challenge to try to explain to people that even though we haven’t had a big flood recently, we do have flood plains, there is a high risk and we do have regulations that you to have to follow,” she said. People would build their homes just outside of the 100-year flood plain so they could have a basement, and they would push back against the building elevation requirements. “Now that we’ve actually experienced a big flood event, I have had a few people come up to me and say, ‘I didn’t want to comply with these flood plain regulations at the time, but I am glad I did; the measures I put in helped save my house,’” Knapp said. “I think now that we’ve had this flood, people are going to take it more seriously than they did in the past.”