On some roads in Boulder County, Colorado—including this portion of Colorado State Highway 7—the September flood waters took out the roadway and the base beneath, altering the river channel. Courtesy of the Colorado Department of Transportation
Crews are working around the clock to rebuild major highways that were completely washed away in September flooding.
October 29, 2013—Construction teams in Colorado—some working around the clock—are racing to meet a December 1 deadline to have all of the more than 400 lane miles of roads and highways that were damaged by extreme flooding in early September reopened to traffic.
The teams have made great progress in repairing more than 300 lane miles of the mountain canyon highways that were damaged by powerful flood currents created when a cold front stalled over the state on September 9 and delivered more than a year’s worth of precipitation to Boulder County in just five days.
The focus now is on badly damaged sections of U.S. routes 34, 36, and State Highway 7, on which approximately 90 lane miles of the roadway and the base that supported it were destroyed. In some cases, the path of the river was altered by the flooding and crews are working to return it to its historical channel.
“It’s unprecedented,” says Amy Ford, the director of communications for the Colorado Department of Transportation (CDOT). “We have never ... experienced a disaster of this magnitude. We are looking at damage estimates right now going up to $450 million. It’s something altogether unique for the agency.”
Rebuilding these last 90 miles is a massive undertaking. Crews are recycling as much washout, rock, soil, and gravel as possible to re-create the road base, Ford says. “The amount of asphalt, the amount of rip rap, and [other materials] to stabilize these slopes, rebuild some of these bases, and retop some of these roads is pretty extraordinary.”
Ford says the CDOT quickly recognized the magnitude of the situation and developed an infrastructure recovery task force charged with flood recovery. That task force was aided in the early days of the effort by personnel from the Vermont Agency of Transportation (VTrans), who traveled to the state and shared lessons learned from the devastation of Hurricane Irene. (See “Hurricane,” in Civil Engineering online.)
“It started raining on Thursday, and by Tuesday we had [VTrans] members sitting beside us, offering lessons learned from the experiences they had had,” Ford says. A key concept VTrans imparted was a division between an initial response and longer-term recovery. The idea of dividing the Herculean task between response and recovery helped greatly.
“They really helped us recognize that while we were at sprint speed right now, we were in a marathon,” Ford recalls. “The sooner we recognized that, the better. It allowed us to pause and start thinking about how we split this work so we make sure that we hit our short-term goals, but recognizing there is a much longer-term need out there.”
Portions of U.S. Route 34 were especially hard hit by flooding; in
some cases water topped the retaining walls. Crews are racing to
rebuild by a December 1 deadline. Courtesy of the Colorado
Department of Transportation
The short-term needs were exceptionally pressing. In the immediate aftermath of the flooding more than 30 major highways were closed. During the first two weeks, the CDOT, contractors, and the Colorado National Guard operated crews around the clock whenever possible to open roads. Some corridors that remain closed are still not safe enough for nighttime construction.
Early efforts to assess the damage produced a startling discovery. Although the floods had damaged 120 bridges, not a single span had been damaged beyond repair. Not all of the bridges are open, however, because in some cases they are isolated by missing roadway approaches.
“We’ve had two bridge inspection crews working nonstop since mid-September to assess all of these bridges,” Ford says. “As you look at the aerial photography, what you could see was a lot of damage on the roadways coming up to the bridges and some of the bridge decks. But as you got into it—looking structurally [at] girders, piers, et cetera—there may have been some scouring, but the facilities themselves were still stable. So that was something we were very pleased, frankly, to see.”
Ford attributes this in part to design changes the agency implemented following flooding in Big Thompson Canyon in 1976 that killed more than 140 people, some of whom were never found.
“It was absolutely designed to be as flood resistant as they could make it,” Ford says. “There is still significant damage in that corridor—upwards of 80 percent damage on the roadway and bridges there.” Much of that damage occurred because flood waters topped retaining walls.
The response phase is scheduled to conclude on December 1. By then all of the damaged roads are scheduled to be open, although some of the roads might be temporary, with gravel surfaces. Winter is fast approaching in the mountainous state and laying asphalt will soon be impossible. “The weather is not our friend,” Ford says.
Once the CDOT enters the recovery phase, engineers will begin to focus on more permanent solutions for the roadways, bridges, and river retaining structures, working with river hydrologists. That phase of the project will likely last several years.