FLOOD07652

• County: Boulder
• County: Larimer
• Stream Name: Big Thompson
• Basin: South Platte
• Title: The Big Thompson Flash Flood: What If It Happened Again
• Date: 1/1/1996
• Prepared For: CWCB
• Prepared By: Henz Meteorological Services
• Floodplain - Doc Type: Flood Documentation Report

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Existing system

Even a flood-scarred optimist like myself will admit that the system now and in the near future will
be less than perfect. It will require creative, intuitive, and even, inspired thought and the heart to
commit the thought to action by dedicated individuals and teams to make flood warning systems
and plans work. Recent NWS documentation suggests that flash flood prediction and warning is
getting better but for the last ten years:

. Most flash flood warnings are issued during or after the flash flood.

. Most flash floods occur without either the issuance of a flash flood watch or warning.

. Most flash flood watches are false alarms.

. Most flood detection networks do not provide enough lead-time for effective pro-active
response to take place.

These facts are an affirmation that the prediction of flash flooding is still a very difficult task
despite the research contributions of the past two decades. Basin specific warning prior to the
event is still the exception rather than the rule. FLASH FLOOD PREDICTION AND WARNING IS
A VERY DIFFICULT TASK. Reliance solely on the NWS flash flood watches or warnings to
activate responses or put warning programs into a state of readiness may be asking too much of
the existing system. The new technology of the modernized NWS places a premium on
detection rather than prediction to provide a warning. It relies on a dwindling number of
operational meteorologists to interpret the information flood and issue timely watches and
warnings from remote locations.

For these reasons I reserve judgment on the new system and urge a continued local solution to
the flash flood warning dilemma. In the final analysis I believe that flash flood warning will become
and is a local issue. I offer the following six points as a reminder from the Big Thompson tragedy
for your pondering:

. Flood plan management: Know where your problem basins are, move people out or
find a creative warning system that works.

. Basin-specific warning plans can save lives. Even a warning plan that fails offers more
structure for decision-making than the chaos of no plan at all. Individuals can rise to
the occasion but need some structure to succeed.

. Flash floods must be predicted and detected for effective warning. Interactive local-
federal government solutions that work exist. Use one of them.

. Basin rain gauge/stream gauge/weather station networks can provide the needed
quantitative information for proactive response and evacuation decisions.

. Emergency flash flood response must be proactive to succeed and be planned and
delegated to function

· Despite all your work and good intentions, Murphy will be there to test your system.
The flash flood will occur on a holiday weekend during periods of minimal staffing
when resources are at a minimum to respond.

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