Excuse my language, but: Holy. Shit. That's what all of us natural disaster-curious Internet voyeurs were thinking last week, our jaws giving in to gravity as we clicked through images from Colorado's Front Range of people trudging through baseball fields covered hip-high with water, roads sliced apart by whitewater, and cabins transformed into riverine islands. Weather Channel CEOs were, no doubt, rubbing their hands together and cackling, while the usually staid 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 before."
Well, yes and no. The amount of rain that fell on communities like Boulder and Lyons was indeed historic, smashing those cities' monthly and daily precipitation records, and devastating many residents. In some locales, it's being called a 1,000-year rain event, meaning there's a 1 in 1,000 chance of such heavy rains in any given year. But it should come as no surprise that Boulder flooded. Crack open the history books and you'll find that the Front Range has always been flood prone. According to the Boulder Area Sustainability Information Network (BASIN), when it comes to flooding, "the Boulder Creek drainage is considered among the most hazardous in the entire western United States." The city sits smack at the mouth of Boulder Canyon, and because its floodplain is so developed, the risks to human safety and property are especially high here.
Boulder owes its vulnerability to geography. It's pushed up against the foothills of the Rocky Mountains and steep-sided canyons. When storms get stuck above it, as they did last week, rains can careen off pitched slopes into the canyons, where creeks swell and eventually burst forth onto the city itself. One of the earliest documented instances of this was in 1894, which incidentally, was also Boulder's last 100-year flood event. Homes, bridges and train tracks were swept away, and the girth of Left Hand Creek apparently grew to a half-mile. Significant flood events have occurred more than a dozen times since.
Other Front Range enclaves located in or near the foothills and canyons are similarly vulnerable. The Spring Creek Flood of 1997 took five lives in Fort Collins, derailed a freight train, and caused some $200 million in damages. Much more tragically, the 1976 Big Thompson Flood west of Loveland claimed 144 lives and 418 homes and businesses. That flood occurred on a Saturday in July, the height of tourist season. Within just two hours, 12 inches of rain fell, most of it on sheer, canyon walls that lacked soil. Many people trying to escape by car on roads built to shadow the Big Thompson River were swept away.
There have been a lot of advances in forecasting flash floods and managing risk since, and perhaps some of them are to thank for the fact that the death toll from these recent floods stands at just four, so far as we know. (Although, certainly, any loss of life is too much.) There are real-time stream gages, for instance, and robust warning systems in place. Big Thompson Canyon now has safe zones people can escape to, and there are fewer buildings in the floodplain. Some land was even purchased by public entities for open space and to prevent risky new development.
Flood preparedness and new development is regulated in Boulder's floodplain, but that didn't happen until after the city had bloomed in the hazard zone – despite warnings from Frederick Law Olmsted Jr., who was hired to make a flood control plan for the city in 1910. "The principal waterway in Boulder is Boulder Creek, and its principal function, from which there is no escaping, is to carry off storm-water which runs into it from the territory which it drains," Olmsted advised. "If, lulled by the security of a few seasons of small storms, the community permits the channel to be encroached upon, it will inevitably pay the price in destructive floods." As employees of the city's public works department wrote in a mid-'90s report on community flood education, it's too bad that "Boulder took (Olmsted's) report and placed it on the shelf for more than 65 years."
Furthermore, it can be argued that the overall risk flash floods pose to life and property continues to increase with population growth in many flood-prone places in the West. Ultimately, managing that risk requires not only good forecasts, warning systems and restrictions on new development, but personal responsibility. That is, if you live in a place where flood-risk is high, pay attention to the weather, and have a plan for reaching high ground. Sounds simple, but it isn't. Social scientist Eve Gruntfest, who has studied perceptions of flood warnings and decision making in their wake, writes that deaths in vehicles are especially common, accounting for up to 50 percent of fatalities in flash floods in the U.S. The impulse to flee by car is strong, despite the fact that climbing to higher ground is nearly always safer. "How to get people to abandon their cars and climb to safety in flash flood situations continues to be a major policy dilemma," Gruntfest wrote in a reflection on Big Thompson Canyon 20 years later. "The public underestimation of the power of flowing water prevails."
Cally Carswell is HCN's assistant editor. She tweets @callycarswell.