Gleaning lessons from floods

A week after the flooding surge had ended, areas adjacent to St. Vrain Creek between Lyons and Platteville remained under water. Photo on Sept. 21/Allen Best
A week after the flooding surge had ended, areas adjacent to St. Vrain Creek between Lyons and Platteville remained under water. Photo on Sept. 21/Allen Best

What lessons can be gleaned from

this Biblical deluge  in Colorado?

by Allen Best

Rains that led to widespread flooding along Colorado’s Front Range were unusual, of course, and even extraordinary. There were frequent references to a Biblical deluge. Meteorologists at the National Oceanic and Atmospheric Administration say that some areas experienced a 1,000-year event while getting doused with up to 15 inches of rain over the course of just a few days.

But what caught the eye of Nolan Doesken and his staff at the Colorado Climate Center was the rainfall patterns. In most such summer rains, the deluge occurs at 7,500 feet in elevation and lower, or in the foothills. This time, rain fell up to the Continental Divide.

“The majority of the water is still from the base of the foothills up to 8,000 feet, according to the U.S. Geological Survey. Our analysis will probably confirm that. But there’s a lot of contribution of elevations above 8,000 feet, which is why water was flowing through Estes Park,” said Doesken, Colorado’s official state climatologist, in an interview on Sept. 19.

“This is pertinent to mountains towns,” Doesken added, “because mountain towns to a certain extent have always been conveniently, climatically immune to the worst of flooding. Estes Park, at an elevation of 7,500, would be at the low end of such mountain towns. Most of the flooding at those elevations has been snow melt caused after blistering sunshine rather than pouring rain.”

Water remained on some roads near Longmont a week after the flood surge passed. Photo/Allen best
Water remained on some roads near Longmont a week after the flood surge passed. Photo/Allen best

Colorado’s Western Slope communities aren’t entirely immune to flash floods. Doesken points to a weather event in 1997 that dropped eight inches of rain along the Park Range, north of Steamboat Springs, in just a few days. There have been some giant, but isolated rain events in such places as the Sweetwater Creek drainage on the edge of the Flat Tops, northwest of Eagle. The strongest parallel in Colorado weather records is a storm in September 1970 in which moisture from the tropics parked over the San Juan Mountains for several days.

Flooding in ski towns, however, is usually a spring event. Even if rain falls in spring, at higher elevations it always turns to snow.

September, however, is a month of potential. The atmosphere can still be warm and hold much moisture. That’s what happened in this storm.

Early in September, Denver had high temperatures of 97 degrees. More noteworthy altogether were the string of nights in which the temperature never got below 60. That’s July weather. Doesken and his staff thought, “This is pretty interesting.”

Is this a harbinger of global warming? That was the immediate chatter in many places, but even scientists convinced that greenhouse gas emissions pose a major threat to civilization are reluctant to connect the flooding from this storm to the greenhouse effect. Mother Jones Magazine delivered a good summary in this story, “Did Climate Change Worsen the Colorado Floods?”

Estes Park bounces back

As for Estes Park, it got hammered hard in this storm, but has recovered, at least superficially, fairly quickly. “We’re open for business,” proclaimed Mayor William Pinkham last Friday, not many days after the city manager, Frank Lancaster, was quoted in an AP story as advising visitors to stay away for a month.

Anecdotal reports suggest that Pinkham was very much correct in saying that the town was ready for visitors. Getting there, however, is another matter. Highways along Big Thompson River and St. Vrain Creek and South St. Vrain were washed away, and by some expectations may remain blocked until January. Travel time from Denver lengthened an hour, to 2.5 hours along the Peak to Peak Highway.

In 1976, when a thunderstorm parked over the Big Thompson Canyon and dumped 10 to 14 inches of rain in four to six hours, Estes Park had no appreciable damage. All the action was downstream. But in 1982, the story was different. Lawn Lake Dam, an irrigation reservoir located in Rocky Mountain National Park, failed. Three to four feet of water swept through the town’s primary tourism venue, Elkhorn Avenue.

This time, there were two feet of water in Elkhorn Avenue, with water up to doorways and, in some cases, flowing into shops. It could have been worse. In the rebuilding that occurred after Lawn Lake Dam, the town made itself better able to handle flooding. Fall Creek converges with the Big Thompson River in the middle of the town. Just a week after the flooding subsided, most businesses had reopened.

Estes still has major rebuilding to do. It lost six miles of road, with gas, water and electrical lines underneath them. Pinkham said city officials are examining what budget items can be cut, what can be deferred. Even so, some projects well underway will get built just the same, especially if they help generate future business. One of those projects is a 33,000-square-foot multi-purpose center.

“We are probably looking at 2015 to get our economy back up, but it’s important to do those things we can to make sure people know we’re not closed for business,” said Pinkham.

“It’s hard to imagine what this town looked like a week ago,” he added. “I’m totally proud.”

Lessons learned?

But what lessons should be drawn from this rain and flooding along Colorado’s Front Range. The most notable takeaway is that even if this is a 1,000-year rainfall event in certain places, a conclusion not accepted by all meteorologists, the flooding was far less. In Boulder, it fell within the framework of a 50-year flood, maybe less. The flooding of St. Vrain Creek, which so heavily damaged Lyons and Longmont, may have been something approaching a 100-year event.

One note: a 100-year-flood doesn’t mean that you have to wait 100 years to have a flood of that size. That’s just the percentage chance on any given year of having a flood of that dimension. You can have two 100-year floods back to back.

In other words, the “big one” is yet to come.

Boulder has done a number of things right in decades past: bigger bridges to accommodate more water, removal of some structures upstream of the city, and wider floodplains in newer areas constructed since the 1960s.

Chris Cares, the principal in RRC Associates, which does considerable work for both resort towns and the ski industry, was a Boulder municipal planner in the 1970s. Now, his office is along Boulder Creek, separated by a set of railroad tracks, a bicycle path and a parking lot. That parking lot had disappeared last week, covered by mud. Only lights and a basketball hoop gave away its previous uses. The  bike/pedestrian path under the railroad tracks had become a culvert for flooding waters. The open space was a place of waterfalls, streams and rapids. “It’s very impressive, and it’s all open space lands and land that was designed to convey the flows. It was put to a test early on,” says Cares.

A bike and pedestrian path below railroad tracks was filled to within two feet of the top by sand in recent flooding. Photo Sept. 25/Allen Best
A bike and pedestrian path below railroad tracks was filled to within two feet of the top by sand in recent flooding. Photo Sept. 25/Allen Best

“It’s clear that planning efforts made a difference,” he says. However, he expects a great deal of tweaking to come. Just one example: warning sirens went off so often during the flooding that they were like the proverbial cries of wolf.

Many questions remain. How much should a community invest in a 200-year flood event? How much can it afford? Well-heeled Boulder did pretty well handling this 50-year event, but even so there were problems in some residential areas, where water cascaded off slopes. And the flood there in 1894 delivered more than twice as much water, about 13,000 cubic feet per second, as compared to about 5,000 cfs this time.

While Boulder Creek handled flows, tributary creeks bounded out of their banks, causing considerable damage and, on these tennis courts, a mess. Photo Sept. 24/Allen Best
While Boulder Creek handled flows, tributary creeks bounded out of their banks, causing considerable damage and, on these tennis courts, a mess. Photo Sept. 24/Allen Best

In nearby Lyons and Longmont, the questions are more difficult yet. Do you prevent people from living in 50-year flood plains? Or 100-year floodplains?

Rolling climate dice

A broader, more difficult question is how much this sort of rainfall represents the future? Climate scientists—even those very, very worried about accumulating emissions—were quick to say no, that you can’t connect the dots of global warming and these biblical rains. But greenhouse theory does hold that storms will become more intense as the atmosphere gains increased energy.

However, ssome climate change scientists have been saying that global warming is becoming evident in the extremes of weather. Records are being broken when natural variability, such as El Niño, works in the same direction as human-induced warming, said Kevin Trenberth, of the National Center for Atmospheric Research in a speech at the the American Meteorological Society’s annual meeting in 2010. “Most of the time, the climate and the weather you experience are the same as you experienced before. It’s only out here on the tails of the distribution that you are really experiencing something different,” he said. Last fall, he said he believed Hurricane Sandy may have had 10 or 15 percent more energy as a result of global warming. You can see more about this debate at a 2011 story I wrote called “Is the more intense weather predicted for global warming evident at edges?”

To be clear, there is disagreement about scientists on this matter. Hydrologists, in particular, seem to think the evidence of more intense rainfall just hasn’t been found.

Brad Udall, director of the Getches-Wilkinson Center for Natural Resources, Energy and the Environment at the University of Colorado, points out that global temperature increases have been minor as compared to what is predicted.

However, scientists say that globally, the atmosphere has gained about 5 percent more moisture in the last 50 years. “It’s a factor, but a very small factor,” said Martin Hoerling, a meteorologist with the National Oceanic and Atmospheric Administration, at a forum in Boulder on Wednesday. He also pointed to a flood in 1938  in the same area of Colorado that had striking parallels. “Nature has a way of delivering without human intervention.”

Be assured that this effort to assess  the influence of greenhouse gases on weather will only continue.

Looking forward, looking back

In my travels during the last two weeks, I only got a glimpse of the great power of this water and the destruction it has wrought —and this is just a 50- or perhaps 100-year flood. I haven’t seen the homes destroyed in Lyons, Longmont and Jamestown, nor the carnage in Big Thompson Canyon. Will people there rebuild again, as they did after the 1976 flood?

As a human species, we tend to forget. We know about flooding, but it’s an intellectual thing, an abstraction. But even when we know it form direct experience, it’s easy too forget after 10, 20, or more years. Much harder yet is imagining a future that’s not quite like anything in our recorded past.

Allen Best

2 thoughts on “Gleaning lessons from floods”

    • Not at all. Especially love it if you provide a link. Of course,t hat was written in September. A deeper understanding now, including site visits to many of the flooded areas.

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