Natural Hazards Observer
| March 2004 | Volume XXVIII | Number 4 |
Disasters Waiting to Happen . . . Second in a Series
Comments on the 2009 Boulder Flash Flood:
Closing Remarks from the 2020 Natural Hazards Workshop
In 2009 the snowpack in the mountains above Boulder, Colorado, was far above average; the ski season lasted well into April, and even in June diehard skiers were hauling their backcountry skis to the Indian Peaks snow-fields. Frequent rains drenched the Front Range, and by May, the reservoir 18 miles above Boulder on Boulder Creek, was overflowing. With saturated soils and rapidly melting snow, the rainstorm that stalled 12 miles from Boulder on June 21 was all it took to produce a devastating flash flood.
The last great flood occurred in 1894 when the hills in the canyon above town had been denuded by miners and loggers, contributing to the high creek runoff (see http://bcn.boulder.co.us/basin/gallery/flood1894.html). By 2009, increased housing and roads had offset the benefits of reforestation, and water again ran quickly off hillsides and roadways into the creek. Five inches of rain fell in less than five hours, and Boulder Creek, which normally runs at 300 to 600 cfs (cubic feet per second), quickly reached 12,000 cfs.
As is typical with such events, officials worried about the appropriate time to sound an alarm. The time required to warn the public of a flash flood in Boulder is longer than the time it takes a flood to form and reach the city, and the decision to announce an imminent flood and sound a warning must be made before enough rain has fallen to be certain that a flood will occur. Boulder officials feared losing credibility by sounding an unnecessary alarm; they also feared not sounding an alarm soon enough for people to evacuate.
A flood warning was issued and 20 minutes later reports from upstream indicated that a 10-foot wall of water had formed nine miles up the canyon. Forty-five minutes later the deluge arrived at the mouth of the canyon just west of Boulder and inundated the city. The torrent that reached Boulder was not just water-it included branches, whole trees, wreckage from destroyed and damaged homes, pieces of private-access bridges, yard equipment, cars, sheds, rocks, silt, propane tanks full of gas, other debris, animals, and human bodies.
Most of the city's bridges were designed to break away on one side in a flood, but one bridge jammed and failed to do so, and far more damage occurred behind the bridge than had been predicted. Moreover, when the resultant debris dam finally gave way, a mass of concrete, asphalt, rubble, and far more water than anticipated by any flood model spread north to blanket residential areas and parts of downtown. Hundreds of parked cars throughout the city were picked up by the floodwaters and carried down streets; others were swept away in the floodway to become half-ton torpedoes.
The flood resulted in 24 deaths and hundreds of injuries. One-third of the deaths occurred when people tried to traverse flooded intersections in automobiles, not realizing that 18 inches of moving water can carry a car away. Many of the casualties were people who had gone to the banks of the creek to watch the rising waters, and several were transients who were camping under one of the creek bridges.
Direct damage was estimated to exceed $250 million, but that did not take into account the losses that could not be quantified, such as the psychological effects on families directly affected, aesthetic damage, lost wages, and environmental degradation.
Flood Was Not Unforeseen
By the mid-19th century, the miners and settlers around Boulder had heard stories of catastrophic flooding from the Southern Arapaho tribe, which had inhabited the region for 200 years. Floods were common during the early years of the town's development. Over the years, smaller floods reminded citizens and policy makers that the risk remained (see http://bcn.boulder.co.us/basin/history/floodhistory1.html), and concern increased markedly when the Big Thompson flash flood, 40 miles north of Boulder, killed 139 people in 1976, and a flood hit nearby Fort Collins in 1997. In the 1990s, Boulder was rated as the city in Colorado where people were most likely to experience a catastrophic flood, and one prominent flood researcher, my great grandfather, actually established a research protocol for the great flood when it inevitably happened (see http://www.colorado.edu/hazards/bcfn/).
This history, along with remediation activities required under the National Flood Insurance Program and the regional Urban Drainage and Flood Control District, led Boulder to enact flood mitigation improvements in the latter part of the 20th century. The city and county adopted a warning system, a high-risk property purchase plan, and a nationally recognized greenways project that resulted in multipurpose riparian parkways containing heavily used bike/walkways, recreation parks throughout the city, restored stream habitat, breakaway bridges, and, most importantly, floodplain use that did not increase the exposure of property and life to floods. There were signage and education plans in place to serve citizens, tourists, and international visitors. Interestingly, however, the city's buyout policy had been successful in removing only a portion of the residences in the floodplain; when the flood hit, the city itself lost several of its own buildings.
And now we come to a confluence ourselves-in the aftermath of the 2009 flood, Boulder was faced with two distinct and opposing courses of action, each bringing with it different consequences. We know that the history of flooding in the 21st century has yet to be written and what happens in the years to come is not cast in stone. Rather, it depends on the choices made here (and in Tulsa, Greensboro, Fargo, Scituate, Santa Barbara, and a thousand other places across the nation).
One Path
The events of 2009 led citizens and government alike to reexamine the steps already taken to mitigate floods. Although the flood was an "extraordinary event," the Boulder Creek Watershed Initiative, supported by local government leaders, built upon the momentum of the disaster response to create a more flood-resilient community through improved land-use decisions, an improved warning system, better disaster planning, and innovative hazards education.
We are living with the legacies of these decisions today. Flood resiliency has emerged as one of a larger set of community goals involving ecological, social, and economic sustainability. When the city of Boulder reviewed its pre-2009 disaster preparedness and mitigation actions, planners and citizens came to recognize that hazards issues could not be divorced from larger questions about sustainability and the city's environment. Collectively, we began to examine potential alternatives regarding a range of issues, beginning with flood and wildfire hazards.
I am happy to say that overall, we are successfully focusing on long-term solutions to complex problems. Through the long process of citizen participation, we have begun to manage our floodplain in a holistic way in accordance with the precautionary principle, which advises that in the absence of absolute proof, a strong hypothesis that catastrophic losses are possible should be enough to encourage precautionary action. We have widened the floodplain to create catch basins for stormwater-a means to mitigate flooding-created a wildlife corridor, bird sanctuary, hiking trails, recreational areas, and community gardens. We have improved the city's warning systems by placing unobtrusive, highly reliable solar warning devices in neighborhoods, within earshot of most residents. The community has initiated an aggressive comprehensive educational program about floods, wildfires, and other local hazards for both citizens and school children. The university has also played a significant role in post-flood disaster mitigation, bringing academic researchers, government officials, and practitioners from engineering, physical and social sciences, and policy studies together to build relationships that foster comprehensive solutions to natural disaster problems.
Another Path
The people of Boulder came together following the flood of 2009 and helped one another sort through the devastation, clean up, and grieve for all that had been lost. That goodwill lasted for a few weeks during which we focused on responding to the tragedy. Unfortunately, grief and compassion were replaced with a search for someone to blame and an emphasis on quickly rebuilding what had been lost. Despite pleas to wait until floodplain management studies had been completed and maps updated, people wanted to rebuild as quickly as possible-to both erase the memory of the tragedy and resume their lives and livelihoods.
The ensuing debate was contentious and exacerbated by the fact that our recovery plan, written in 1998, was out of date. There was support for removing all structures from the floodplain, but many property owners argued that they had a right to rebuild on their land as they saw fit. Having received flood insurance payments, they were determined to use the money to re-establish their homes and businesses. Under pressure to spend federal disaster funds given to the city, and faced with a tangle of law suits, the city quickly came up with a plan that focused largely on capital rebuilding. We had no funds for an education program, and because of budget constraints and fiscal difficulties brought about by the flood recovery, a number of proposed open space tax increases failed. Unfortunately, by 2013 Boulder looked remarkably similar to Boulder 2009, with new university dormitories sited at the edge of the floodplain. Then the great flood of 2014 struck. . .
- This Invited Scenario comprises the fictionalized remarks of Gilbert F. White, IV, during the 2020 Natural Hazards Workshop.
The editors gratefully acknowledge the valuable information provided by Dennis Mileti in Disasters by Design (Washington, D.C.: Joseph Henry Press, 1999) and the web sites of the Boulder Flood Notebook (http://www.colorado.edu/hazards/bcfn) and the Boulder Area Sustainability Information Network (http://bcn.boulder.co.us/basin).