A 50-year flood and 1,000-year event?
Putting Colorado’s floods into context
Destructive flows different and in some cases less than those in Big Thompson canyon in 1976
by Allen Best
The recent rainfall along the Front Range was phenomenal, by some estimates a 1,000-year event in terms of duration, volume and area. But the flooding?
Not so much, at least as measured by an obelisk along Boulder Creek in downtown Boulder.
Human memories about weather are unreliable. During many years living in Vail, how often did I hear that the latest powder storm was absolutely the best ever? Plenty. Flooding is like that, too, but maybe in reverse.
The turquoise obelisk in Boulder provides a better measure against long-term memory loss. Located near the Broadway bridge, it provides benchmarks for flood levels. The water this year lapped against the 50-year marker. Above it are others: 100 years, 500 years and, much higher yet, Big Thompson, a reference to the giant flood in that canyon between Loveland and Estes Park in 1976.
I was at the Big Thompson disaster. I was living in Fort Collins then and was among scores of young men (sorry, women, those were different times) with strong backs who could be summoned in case of forest fires. My only fire was at an old sawmill site in the foothills. The joke was that one of us had set the fire because we were so desperate for minimum-wage work.
Then came July 31. It was hot that night in Fort Collins. It hadn’t rained a drop.
I was living above Gene’s Tavern, just two blocks from the Larimer County Courthouse. When the call came, I was at the sheriff’s office almost immediately. It was 9 p.m.
Being among the first at the command center at the Dam Store west of Loveland, near the mouth of Big Thompson Canyon, I was assigned to a pickup dispatched to look for people in the water near the turnoff to Masonville. Already, the river was out of its banks. From the darkness emerged a figure, dripping and confused. “I went fishing at Horsetooth (Reservoir) and was driving home and then there was all this water,” he sputtered. He was befuddled. So were we.
Our leader decided we’d best get out of there. From what I saw the next morning, that was an excellent decision. Water later covered the road there, too. I spent the night at the Dam Store as the water rose. Helicopters were dispatched, but there was little that could be done. Our lights revealed picnic baskets, beach balls and propane bottles bobbing in the dark, roiling water that raced past us, but never any hands summoning help.
In the morning, we found those hands. The bodies were stripped of clothing and covered with mud. The first I saw was of a woman who we guessed was 18, not much younger than I was then. This thin margin between life and death was startling in my young eyes.
Eventually, 144 people were declared victims of the flooding that night (although one turned up alive in 2008 in Oklahoma).
Estes Park got some rain, but not all that much. The larger story was partway down the canyon, in the Glen Haven and Glen Comfort areas, where the thunderstorm hovered. In just a few hours, it dropped 10 to 14 inches of water.
Downstream in the canyon, just above the Narrows, some people were unaware that anything was amiss until they went outside their houses and saw the water rising in their yards. It hadn’t even rained there. One cabin I saw a few days later was stripped of doors and windows but stood on its foundations, a mound of mud 5 or 6 feet high in the interior. I seem to recall a dog barking as we approached, protecting that small part of the familiar in a world gone mad.
At the old hydroelectric plant where my family had once enjoyed Sunday picnics, the brick building had vanished. Only the turbines and concrete foundation remained. In a nearby tree, amid the branches maybe 10 or 15 feet off the ground, hung a lifeless body.
The river that night carried 32,000 cubic feet per second of water at the mouth of the canyon, near where I was stationed. It happened almost instantaneously — and then it was gone. It was a flash flood.
This year, the flows peaked at 10,000 cfs, but were more sustained and, according to reports, the damage inexplicably greater in portions of the canyon. There were horrors, too, but this year there was time for warnings.
After the 1976 flood, rain gauges were sprinkled in the foothills of the Front Range, up to 7,500 feet in elevation, where most heavy summer rains occur. That telemetrically transmitted information alerts police chiefs and sheriffs to flooding potential. That warning system may have saved lives this year.
Where does volume of this flood fit into the context of flooding in the last 150 years? That answer will have to wait. Many rain gauges were swept away, so peak flows will have to be calculated during field visits by U.S. Geological Survey personnel. That will take several weeks.
One more banner of comparison was 1965, when rivers and creeks from Castle Rock to Lamar to Fort Morgan flooded.
The flood that swept through Littleton and Denver created a mess, but led to the rethinking of the South Platte River as an asset rather than industrial afterthought.
East of Denver and Colorado Springs, the same storms transformed Bijou Creek from a lifeless expanse of sand into an angry, snarling mass of water. At Fort Morgan, after entering the South Platte River, it nearly submerged the arches of the Rainbow Bridge. This year’s flooding, according to several eyewitness accounts, didn’t even come close.
We’ve had other floods, too. Even in the midst of the Dust Bowl, there were giant floods in eastern Colorado, both on the South Platte and in the Republican River. The floods in Pueblo in 1921 may have been the most destructive ever in loss of life; perhaps 1,500 people drowned.
My guess is that this flood will be the most damaging ever in Colorado history in cost to property. Part of this is due to how broad the inundation was, from Colorado Springs to Wyoming. Population growth is also part of the story. Colorado now has 5.2 million people, almost double that of 1970, most of us crowded between Castle Rock and Wellington, a good many in the foothills, those areas so vulnerable to fires but also flooding.
This flood once again points to the importance of land-use planning. Where you put sewer plants does matter. You can’t anticipate every natural disaster, but floods have an element of predictability.
Boulder has had big floods before, most notably in 1894. It also had the direct lesson of Big Thompson and the local influence of Gilbert White, who died in 2006. “Floods are ‘acts of God,’ but flood losses are largely acts of man,” he had said. Boulder has muddy feet, but the consequences would have been much worse had the city not taken his advice and removed structures from along the creek to the west and resized bridges to accommodate more water. The obelisk is in his honor.
John Pitlick, a hydrologist at the University of Colorado, says the flood this year peaked at about the 50-year marker on the obelisk.
In one of his classes, he also noted that rainfall and flooding aren’t one and the same. “It is possible from a statistical analysis to be a 1,000-year rain, but you don’t necessarily have a 1,000-year flood.”
In other words, context matters entirely. Had the water fallen in a shorter time, such as it did in the Big Thompson in 1976, Boulder’s story almost assuredly would have been different. “We might have seen a catastrophe,” he says.
That leaves us in something of a no-man’s land, as Pitlick puts it.
This year’s floods were a big deal and certainly a blow to irrigation infrastructure and roads. But it was not catastrophic to Colorado the way the flood to Pueblo was in 1921. What lessons do you draw for future flood planning? That’s the question for communities along the Front Range in months ahead.