Lessons from the flooded Front Range

The floodwaters that swamped 20 counties on Colorado's Front Range last month rose and spread with mind-boggling strength. Rushing mud and water sliced a downtown Boulder office building in half; asphalt roads crumbled under raging whitewater. Afterward, drums dislodged from gas pads reclined in the muck like empty beer cans. The storm dropped nearly a year's worth of rain in a few days, destroying 1,800 houses, causing some $2 billion in property damages, and killing at least eight people. The National Weather Service called the rains "biblical." "There's no scientific definition of 'biblical,' " reported Climate Progress, "but the flooding has been unlike anything local residents have ever seen."

Actually, that's not entirely true. This storm did smash precipitation records, and its timing, duration and breadth were unusual. Drenching rains usually arrive earlier in the season, soak smaller areas and dissipate quickly. This one lingered for days over an entire region. Still, neither the storm itself nor the widespread flooding it caused were totally unprecedented: A nearly identical event occurred in 1938. The difference is that, this time, there were a lot more homes, roads, sewage pipes and gas wells in the water's path. And they were mutilated.

The truth is that, with or without climate change, the Front Range has been and always will be flood-prone. Destructive floods of various magnitudes have hit communities there more than a dozen times in the past century. The challenge for planners is to learn how to cope with this inevitable problem, and steel communities against loss of life and property.

And Boulder may be the ideal classroom: The city faces some of the highest flood hazards in the West. It's lodged against the foothills of the Rockies and steep-sided canyons. When storms stall out above it, rains can careen off pitched slopes into canyons, where rivers swell and eventually burst onto the city itself. (Downtown is only one mile from the mouth of Boulder Canyon.) One of Boulder's earliest documented floods -- and one of the worst to date -- hit in 1894. Homes, bridges and train tracks were swept away, and the normally diminutive Left Hand Creek reportedly swelled to a half-mile in width.

Sixteen years later, the city hired Frederick Law Olmsted Jr. to help chart its future growth. Among his recommendations was a warning on floodplain development: "If, lulled by the security of a few seasons of small storms, the community permits (Boulder Creek) to be encroached upon, it will inevitably pay the price in destructive floods." His counsel was ignored. In the 1950s, geographer Gilbert White picked up Olmsted's torch and relentlessly fanned its flame. Now called "the father of floodplain management," White urged Boulder to prepare for the next deluge by ceasing haphazard development in the floodplain and using that land for open space instead.

White, too, was largely shrugged off -- until 1976. That year, northeast of Boulder, the Big Thompson Canyon Flood tore down a steep canyon on a Saturday in July, at the height of tourist season. Twelve inches of rain fell in a few hours, much of it on sheer rock walls lacking soil to absorb it. More than 140 people perished, and 418 homes and businesses were destroyed.

It was, at last, a wake-up call. Boulder officials and residents realized they had been lucky to escape more catastrophes. The city now has some of the more proactive floodplain regulations in the country. In the highest risk areas, it's removed some residential buildings, and no new residences can be built. (They don't want people sleeping in the hazard zone.) Existing buildings must be modified to minimize flood damage. Bridges across Boulder Creek have been raised, and none were lost last month. Though preliminary estimates put damages at $49 million, it likely would've been worse without good planning, says Clancy Philipsborn, a retired disaster recovery consultant. Not that Boulderites should rest easy. Boulder Creek only reached 50-year flood levels, he points out. "This wasn't the Big One on Boulder Creek."

Just as the human landscape shifted in the wake of disaster, so, it appears, has behavior. Eve Gruntfest, a student of White's, calls the response to the rising water "a big success story." Gruntfest, a research scientist with the University of Colorado-Colorado Springs' Trauma, Health and Hazards Center, did her master's thesis on the Big Thompson Canyon flood and the actions people took that saved or cost them their lives. Many perished attempting to flee by car. Indeed, about half of all flash-flood fatalities in the U.S. occur in vehicles. Studies on why people insist on driving through high water have found that some think it will be fun; others risk it if they have somewhere important to be, often work.

"In 1976, 144 people died from a much more precise, localized event," Gruntfest says. "This time, it looks like only 10 people died in a regional flood. What's really remarkable to me is that people weren't out driving when the roads were washed away." Keeping people off the road during floods has long confounded emergency managers, she says, even as flood forecasting and early warning systems have improved. Figuring out why they stayed home this time could help save lives in future floods.

Gruntfest speculates that with so many businesses closing, fewer workers had to weigh the risk of losing their job against possibly losing their life. Communication and pre-planning between forecasters, emergency managers and the media may also have made a difference. Or, she adds, maybe "it was raining so much, people got the idea they didn't want to go outside." As White once famously observed: "Floods are acts of God, but flood losses are largely acts of man."

• Growth & Sustainability