This Article Originally Appeared in the Denver Post July 30, 2006

Lessons from a killer flood
By Tom Browning
 

Searchers look through a car in the Big Thompson River west of Loveland. Some of the victims of the flood were found in their cars. (Post / Dave Buresh)

Nearly 30 years have passed since the devastating flash flood on the Big Thompson River, set off by a severe rainstorm that stalled over Larimer County between Estes Park and Loveland on July 31, 1976. The storm dumped nearly 8 inches of rain in one hour, and up to 12 inches of rain in just a few hours, causing the normally tranquil river to swell into a raging torrent of death. The tragedy claimed 144 lives and destroyed more than 400 homes. Damage estimates were in the tens of millions of dollars.

The peak flood flow on the Big Thompson was computed to be just over 30,000 cubic feet per second (more than 13 million gallons of water per minute) as it swept through the river canyon and the community of Drake. Remnants of houses washed downstream and ended up on top of bridges, cars were smashed into unrecognizable heaps of metal by giant boulders that tumbled down the river in the swiftly moving water, and portions of U.S. 34 were completely torn away from the mountainside.

But the Big Thompson Flood does not stand alone as the only major flood in Colorado history, and similar floods likely lie in our future.

Other devastating floods of the past include the enormous one on the Arkansas River in 1921 that killed about 350 people and left behind a swath of destruction in Pueblo, followed by another large flood in 1935 on Fountain Creek that left its powerful mark on Colorado Springs. During the second half of the century, the Great Flood of June 1965 was not only deadly but wreaked enough havoc in Castle Rock and Denver to cause nearly $1 billion in damage (2006 dollars). My grandfather lost nearly everything when his entire business was washed away in the raging waters of the '65 flood.

Extreme high water from rapid snowmelt during 1984 in western Colorado resulted in widespread damage and a multicounty disaster declaration. The 1997 record flood on Spring Creek in Fort Collins caused five deaths and triggered a presidential disaster declaration, with approximately $200 million in property damage in that city.

I've witnessed the impacts of several other appalling floods during my professional career, including the 1996 Buffalo Creek flash flood in Jefferson County, the 1997 Spring Creek flash flood in Fort Collins, the 1997 Pawnee Creek flood near Sterling and the 1999 Arkansas River flood in North La Junta.

The Big Thompson flood destroyed sections of U.S. 34 and other infrastructure, such as the water pipes shown here. (Post / Dave Cupp)

Many lessons have been learned from that fateful day in 1976 and from similar disasters, most of which have guided the way engineers, government planners and flood specialists think about public health, safety and welfare. Those lessons relate to how humans react during frightening emergency situations, and how extreme events should be analyzed to improve peak flow computations for streams in the region.

Technological advances in recent decades have also greatly assisted in protecting life and property. One tool that water management officials use now is an extensive network of automated streamflow and rainfall gauges located throughout the state. Those instruments are able to report valuable data on a real-time basis, through satellite telemetry, for immediate use by decision-makers.

The National Weather Service uses NEXRAD Doppler radar and rainfall algorithms to assess storm threats and to issue flood "watches" and "warnings" when specific counties may be at risk for potential or actual flooding. The communication tool known as "reverse 911" has been successfully used to warn residents about looming danger and was recently put to the test in Douglas County to notify people about the flooding along West Creek that tore apart a 10- mile section of Colorado 67.

Other warning methods include cellphones, pagers and e-mail messages.

In today's system of floodplain management, the Colorado Water Conservation Board works closely with federal and local partners to help encourage wise land-use practices and flood prevention. The board has several programs to assist in flood-loss reduction, such as managing Federal Emergency Management Agency floodplain mapping studies, completing flood hazard mitigation projects, conducting flood outlook and research, providing post-flood technical assistance to provide damaged communities with information about future protection measures, and implementing watershed restoration projects.

Yet even with all of the work being done and available new technologies, we will continue to experience flood damage.

Why? One key reason is that current standards for development generally balance the risk of serious flooding against demand for development. So development is allowed in areas where there is some risk.

However, flood-producing rainstorms and other factors can cause rivers, streams and creeks to rise beyond their "regulatory" flood levels and above the acceptable level of risk.

The regulatory standard commonly accepted in Colorado and nationwide is the "100-year flood event," a term that's often misunderstood by the public. That standard actually indicates a flood having a 1 percent chance of being equaled or exceeded in any given year, rather than a flood that occurs only once every 100 years. That means it's not impossible for a community to experience 100-year floods in consecutive years.

The cost of public-works projects is another important consideration explaining why communities are still vulnerable to flooding. For example, what if all new roads and bridges were required to withstand or pass much larger flows than what they currently can handle?

One can imagine that many taxpayers would not be willing to swallow the very expensive pill that would be required to replace infrastructure to accommodate the higher design standards.

It's like the question all of us ask in our personal lives: How much risk am I willing to live with in everyday life, and what is an acceptable cost to reduce that risk?

There are several influential experts who believe that current floodplain standards are too low, and that standards should be raised in order to reduce flood vulnerability.

For example, some other countries use a 500-year, 1,000-year, or even greater standard for floodplain development, especially for critical facilities such as hospitals, police stations, fire stations and essential government buildings.

The water conservation board recently suggested a minimum 500- year standard for construction of all new critical facilities. We hope that communities will take this to heart, since land-use patterns, floodplain regulations and issuance of building permits in Colorado are governed at the local level.

Still, there are things individuals can do to protect themselves:

  • If you live in a flood-prone area, buy a flood insurance policy for your home since regular homeowner's policies do not cover flood damage.

  • Do not drive over flooded bridges or into flooded streets.

  • Understand the danger of multiple hazards. For example, previous wildfires in forested areas can greatly increase storm runoff, flooding and debris flows.

  • Be aware of changing conditions if you live, travel or camp in canyons and along waterways, because a wall of water moving swiftly down a stream can develop in a matter of moments.

  • Climb to safety by seeking high ground if water is rapidly rising or if flood danger is imminent, even if it means leaving your car.

The Big Thompson flood left an indelible mark on Colorado history, and it should make us pause and think about how vulnerable we are to rare but probable events. We must remain diligent in the effort to reduce adverse impacts to life and property.

As President John F. Kennedy said, "There are risks and costs to a program of action. But they are far less than the long-range risks and costs of comfortable inaction."

Tom Browning is chief of flood protection for the Colorado Water Conservation Board and chair of the Colorado Association of Stormwater and Floodplain Managers.