Weather records in Boulder began in 1893, just in time to record a massive flood in 1984 when Boulder Creek went out of its banks several block wide, according to Bob Henson of the National Center for Atmospheric Research in Boulder.
The epic flooding that struck river and creek valleys in the northern Front Range and points east earlier this month was higher than any of those since 1894, “higher than any of those in that almost 120 year history, so in that sense it was a 100 year flood,” Henson said. But in terms of amounts of water running through as measured by the U.S. Geological Survey “it was almost like a 50 or 60 year flood,” he said in an interview with radio station KUVO’s morning public affairs segment.
The rain fall measured in Boulder was indeed historic, he said. The main cell of the storm Wednesday through Friday, Sept. 11-13, dumped well over 10 inches, with the week’s total being 17.15 inches. That brought total rain fall for the year to 30 inches, an all time record for Boulder. “The amount of rain to the amount of flooding is not a one-to-one ratio.”
A 100 year flood doesn’t mean that one will occur once every 100 years as part of a natural cycle, Henson said. “It means in any given year you have a one percent chance.”
There is an “odd polarity” between the state’s drought cycles and flooding, he said. When the atmosphere heats up it holds more water vapor, but the warmth also pulls moisture from the soil.”