On September 12, 2013, the rain woke Eve and Walt Feese. Over the din of water thrashing their double-wide, Eve could hear voices outside. “As I walked to the front of the trailer I saw red lights,” she says. It was two in the morning, and people were racing to their cars. A neighbor pulled up and rolled down his window. “He said, ‘Eva, you and Walt are gonna have to get out of here now. The river’s coming.’”

This was never supposed to happen. When you live in Lyons, Colo., you know where your flood plains are, because a creek flows right through town and it has a habit of getting unruly. But Eve and Walt’s trailer park wasn’t in the flood plain, at least not as it appeared on official maps. Nevertheless, that night their home was destroyed by the worst flood to crash through the creek in decades.

A lot of places that had been considered safe washed away that night. One exception was the city of Boulder itself. Located just 16 miles south of Lyons, this outdoorsy mecca of 100,000 might have suffered far more destruction than it did, but for decades of diligent planning. While Boulder ultimately received a smaller inundation than places like Lyons, it was also far better prepared, thanks largely to the foresight of Gilbert White, a local resident known as “the father of floodplain management.” When all was said and done, the 1,000-year rain event, as described by the National Weather Service, left Boulder damaged but not destroyed, and the city bounced back readily.

The strategies that allowed this to happen were surprisingly simple. “We’ve been focusing not on large engineering solutions, but more on good land-use planning and stewardship,” says David Driskell, Boulder’s executive director for community planning and sustainability. “We don’t do large trapezoidal concrete channels to try to protect life in a flood. We understand our creek is an amenity that people value the 99.9 percent of the time that it’s not flooding.”

For this relatively dry area of Colorado, where kayaks adorn the roof of many a Subaru Outback, Boulder Creek is an object of worship — “the heart and soul of our community,” Driskell says. In the spring it swells with snowmelt from the westward Rockies, but in summer and autumn it shrinks to what you might call a heavy trickle, appearing incapable of ever causing any real destruction.

But people around here know that water can go from harmless to fatal in no time. Many of them can remember the Big Thompson Flood, the deadliest in Colorado history. On July 31, 1976, up to 14 inches of rain fell in a space of four hours, and the Big Thompson River Canyon, just a short drive north of Boulder, swelled from 18 inches to 20 feet within minutes. The 31,000 cubic feet of water per second that raced down the canyon took 143 lives, washing some of the bodies 25 miles downstream.

This is the type of flood that typically strikes this part of Colorado. “When we talk about the Front Range being a flood-prone region, we tend to think of flash floods,” says Kelly Mahoney, a meteorologist in Boulder. These flash floods are caused by short, hard rains funneled by the region’s V-shaped topography. The weather event that hit Boulder in September was different: A torrential, widespread, days-long rainstorm. The amount of water that it dropped was phenomenal. In three days, Boulder County got more rain than it had ever received in an entire month since record-keeping began in 1897. Eight inches fell on September 12 alone. “This pattern doesn’t usually happen here,” Mahoney says. It’s so rare that no one grasped its significance as it began to unfold.

Luckily, Gilbert White grasped it decades ago. A pioneer in the field of urban flood planning, White said cities should accommodate floods rather than trying to hold them back with dams and levees. He also happened to live in Boulder, and established the Natural Hazards Research and Application Information Center at the University of Colorado. It was White who, in the wake of the Big Thompson Flood, pushed Boulder to adapt to the floods of the future. “Floods are acts of god, but flood losses are largely acts of man,” he wrote in his 1942 doctoral dissertation, “Human Adjustment to Floods.”

This was a radical idea in an age of massive public works projects like the Hoover Dam, when it was assumed that American engineering would tame anything nature could throw at it. “In 1976, if you came to Boulder or any of these Front Range cities, you would be surprised at how different it was, where the creeks were just something that passed under the road… Houses were built right up to the edge,” says Matt Kelsch, a hydrometeorologist at the University Corporation for Atmospheric Research (UCAR). “Gilbert White at the time recognized the fact that what happened in the Big Thompson [Flood] is something that could happen in any of these canyons… and will happen again in the future.”

Under White’s direction, Boulder began to create policies and infrastructure that would save it from the next big flood. The philosophy was clear: A light touch tends to be more effective than a heavy hand. For instance, in the bed of Boulder Creek, drop structures were created out of rocks where the elevation of the creek falls sharply — small waterfalls that concentrate the flow of the water inward to keep it from overflowing its banks. Similarly, placed at strategic points near the sides of the creek were jagged rocks called “rip rap” that disrupt the momentum of the flood. These mechanisms are still found in the creek today, many of them placed near bridges to try to tame the water where it might do the most structural damage.

When a bridge washes out, you’ve not only lost a piece of expensive infrastructure (and a potential evacuation route), you’ve also created a runaway weapon. One thing that made the Big Thompson Flood so deadly was debris — the boulders, trees, cars and mobile homes that the water wrestled loose and shot down the canyon. That’s why, Driskell says, “If you go along the creek, most of the bridges — the head bridges, the bike bridges — are all breakaway bridges so they don’t become an obstacle that water builds up behind.” Each bridge is attached to the shore by a giant hinge, allowing it to swing open, barn-door style. “During a flood, they’ll break away and just let the water flow. Again, a lot of the planning is: How do you just get the water moving through and not create blockages during a flood event?”

Beneath those bridges are bike paths that on a typical day carry the city’s extraordinarily high share of cycling commuters, the second highest in the nation. But during a flood these bike paths become one of Boulder’s most ingenious resilience strategies. When the water rises, the concrete-walled channels transform into rivers, directing the flood waters safely through the city and to the other side. “If you come here in the spring most of the underpasses are closed down because there’s overflow that’s going through the bike path system to move the water,” Driskell says. When a flood is imminent, the bike paths are locked down with gates. In a 100-year flood event, which the paths are designed to accommodate, the paths become raging, self-contained rivers of flood water.

The floodways can only do so much, however, which is why most of Boulder’s hazardous structures — gas stations, water treatment plants — have been moved out of the floodplain. The county, in fact, now owns much of the flood-prone land around it and leaves it undeveloped. “People started taxing themselves in the 1960s to buy land. We’re now surrounded by 48,000 acres of land that we own,” Driskell says. Other places have only started catching up to this strategy. After Hurricane Sandy, New York began buying up wrecked homes and razing them, just so it could leave the land empty.

“It’s really changed the culture of our community,” Driskell says. “At the same time, it’s challenging. We’ve had a number of flood-related planning efforts in recent history where people have said, ‘Why do you want to do this in my back yard? There’s a ditch there, but it never has any water in it.’ Those communities [that resisted flood mitigation efforts] got hit.”

It wasn’t just NIMBYism that doomed these communities, however. The flood hit poorer neighborhoods harder than rich ones, generally speaking, in Boulder and its surrounding towns. Eve and Walt’s trailer park, for instance, was on a low-lying plain alongside the creek. The ritzier homes with the killer views on the slopes above it stayed high and dry. Now the locals are wondering whether the flood will lead to the “Aspen-ization” of these towns if the poorer residents who were washed out can’t afford to come back and rebuild.

“There were several restaurants here in town where all the men used to get together. They’d have coffee in the mornings and then the afternoons,” Eve says. “All of a sudden you’re paying $2 or more just for one cup of coffee, and that doesn’t even include refills.”

New Orleans saw a similar effect after Hurricane Katrina, as the storm’s most vulnerable victims fled for places like Houston and Atlanta while the city grew richer and whiter. Boulder was pretty rich and white to begin with — the average house here sells for over half a million dollars — but even in Boulder, many of the city’s homeless, who live near the creek, saw their encampments destroyed. Those areas, in fact, are now permanently underwater. The flood literally changed the course of the creek.

In fact it changed the city in lots of ways, and already people are talking about how to better prepare for the next one. “We had a lot of culverts that got blocked and water then jumped into places that it shouldn’t have been,” Driskell says. “I think our community doesn’t realize how close we came to a lot of really bad things happening.”

Despite the flood’s impact, this wasn’t even the worst-case scenario for Boulder. The event that Gilbert White really worried about is still due: A massive flash flood that appears with little warning. Which is why the city sees this event as a learning process, Driskell says, a chance to “bounce forward, not just bounce back.”

“My takeaway from Gilbert White’s work is don’t put stuff where it shouldn’t be,” he says. “Yeah, you can put it anywhere and then engineer a solution to try to keep it safe. But is that really the best expenditure of funds? And does that really create the kind of quality of life over time that you want to have? Nature has ways of dealing with water. We sometimes get in the way of those processes… We just need to move the water through our community as quickly as possible with as little damage as possible.”

Will Doig wrote the text for this story. Still Life Projects created the film.