What is a 100 Year Floodplain?

FEMA flood zone designations on flood insurance maps:  100-year floodplain - Is  another term for a Special Flood Hazard Area, referring to any area that has at least a one percent annual chance of flooding.

The term 100-year flood is misleading. It is not the flood that will occur once every 100 years. Rather, it is the flood that has a one percent chance of being equaled or exceeded each year. Thus, the 100-year flood could occur more than once in a relatively short period of time.

Because this term is misleading, FEMA has properly defined it as the one percent annual chance flood. This one percent annual chance flood is now the standard used by most Federal and State agencies and by the National Flood Insurance Program. This term signifies that a structure located with the one percent annual chance floodplain delineated on the flood map has a 26 percent chance of suffering a flood during the term of a typical 30-year mortgage.

On FEMA's Flood Insurance Rate Maps (FIRMs), these areas are darkly shaded and labeled with zone designations that begin with "A" or "V."

* All information deemed to be accurate but not guaranteed.