How often does a 100-year flood occur?
Large floods are often given designations as a "one-hundred-year flood" but
a 100-year flood does not mean that such a flood occurs once every 100 years
; instead it means that there is a one in one-hundred (or 1%) chance of such
a flood occurring in a given year.
Two 100-year floods could occur a year apart or even a month apart -- it all
depends on how much rain is falling or how quickly the snow melts. A "20-
year flood" has a one in twenty (or 5%) chanc
