HUNDRED-YEAR FLOOD

The magnitude of a flood which has one chance in one hundred (i.e., one percent) of being exceeded in any future one-year period. As the occurrence of floods is random in time, there is no guarantee that there will not be two one hundred-year floods within a given year, or that there will be one such flood within a given century (100 years). The boundary of the one hundred-year flood zone is used by the Federal Emergency Management Agency (FEMA) to designated Special Flood Hazard Areas. These areas are plotted on Flood Insurance Rate Maps (FIRMs), which are used in determining the flood risk to structures in the Flood Plain for flood insurance purposes. Also see X-Year Flood.