Floods
are difficult to measure because different areas react differently
to excess water. One tool scientists use is the probability
of certain water flow rates. If the probability of a certain
flow rate is 1 in 100 or a 1% chance then each year there
is a 1% chance of such a flood. On average then, there will
one such flood every 100 years. This gives rise to the term
"100 year flood". However, it is interesting to
note that since each year has a 1% chance of such a flood
that 100 year floods could occur close together. For more
complete information please visit this USGS
site.
