An uncommonly big flood can happen again in Washington at any time.
Across the Pacific Northwest, rivers rose to record levels during November 1995 and February 1996. In December 2007 the Chehalis River rose even higher placing Interstate 5 under 10 feet of water. Why did these big floods happen only 11 years after the last “100-year flood”?
The term “100-year flood” is misleading because it makes people think that it happens only once every 100 years. The term “100-year flood” really means that there is a 1-in-100 chance that an uncommonly big flood can happen during any given year. Perhaps a better term would be the “1-in-100 chance flood”. Flood designations are based on statistical averages, not on the number of years between big floods.
Clark County's many acres of floodplains ease the affects of flooding.
