Almost two years after a historic flooding event inflicted widespread and catastrophic damage across northern Colorado, engineers and hydrologists are working to design more flood-resistant roadways.
In a review of the September 2013 floods, the Colorado Water Conservation Board (CWCB) said 120 miles of state highway was damaged and more than 16,000 homes and 750 businesses suffered damage. Additionally, the floods claimed 10 lives while 18 counties were declared disaster areas. Repair costs for flood-damaged roads are estimated at $590 million, the Denver Post reported in March.
As the reconstruction process continues, Heather Paddock, flood recovery engineer for the Colorado Department of Transportation (CDOT), said that developing resilient roads involves a handful of steps along with the collaboration of other state and federal agencies.
CDOT is currently coordinating with the CWCB to reexamine watersheds in northern Colorado and gather new hydrological data. This new data will better serve them as they design new structures and in some cases, they've noticed that river flow rates have increased compared to previous historical data.
CDOT is looking to utilize engineering advances, whether it's through new materials or strategies, to withstand future floods. One method is to move sections of highway farther away from rivers.
In a recent article on the National Oceanic and Atmospheric Administration's climate website, Chris Sturm, a stream restoration coordinator for the CWCB, described how riverside roadways will be given more separation from the river.
"[We'll] construct a floodplain in between the road and the river so that at high flow events we've got some room on the floodplain to dissipate energy that would otherwise be eroding at the base of the road," Sturm said.
One of the primary reasons roadways succumbed to the flooding was they were not situated on bedrock, according to Paddock. When the floods struck in 2013, the water undermined the embankment material and took the asphalt with it, she said.
Currently, CDOT is orchestrating construction on portions of damaged highways that run through the canyons by pushing in the canyon walls through rock blasting, so roads can sit on top of bedrock.
Farther east in the plains, roads are being built on a rock base or protected by a heavy riprap, or a type of erosion control, that will help prevent water from washing away the road.
Getting roads elevated out of the state's 25- or 100-year floodplain is another part of the process, but in some cases it is not possible.
"We're just trying to harden the roadway surface so when [the water] does overtop and then the water recedes, we still have a road," Paddock said.
Nine different projects are underway and the number of repaired miles, which stands at 11 for CDOT's roads, is expected to increase quickly. The projects vary in size, ranging from shoulder repairs to replacing entire roadways or bridges that were washed away. The timetable to finish all CDOT transportation facilities is by the end of 2017, while permanent completion for roads maintained by counties and cities is expected by 2019.
With a project of this magnitude, there are various challenges, including getting constant communication out to the public, workers out in the field initiating repair work and lawmakers. Then, there are inherent challenges such as inclement weather.
Winter conditions can often extend well into the spring, leaving the state with a shorter paving season than other areas around the country. Also, another flood event this past spring forced a setback as state Highway 71 was overtaken be floodwaters and the rebuild process had to start over.
"It was currently under construction. We were trying to do the permanent repairs. It just so happened that high water hit right at the time that we were under construction, and we lost that same section of road again," Paddock said.
On roadways that had already been solidified by a rock base, the floodwaters overtopped as planned and the structure was left intact.
"That was a good example of where our resilient solution is working," Paddock said.
The three primary factors that forced such severe flooding in 2013 were a large swath of tropical moisture over the Rockies, a large area of high pressure over the Midwest and a storm in the upper atmosphere over the Great Basin, AccuWeather Senior Meteorologist Alex Sosnowski previously wrote. The continuous heavy rain lasted from Sept. 8-15.
Colorado is more accustomed to flash flooding, Paddock said, and while flooding of that magnitude is not very common, CDOT is taking exhaustive measures to develop more durable roads.
In addition to FEMA and the CWCB, CDOT is working in tandem with the U.S. Forest Service, the Bureau of Reclamation and numerous other state organizations. Including other stakeholders and agencies in reconstruction conversations can help deliver better solutions, not just for the roadways but for the state's communities too.
"I think Colorado can take a lot of pride in [working with other agencies], that we really established some good partnerships to kind of have a statewide resilient approach, not just looking at it from a transportation perspective," Paddock said.