The term 100 year flood is misleading, most think it is a flood event which occurs only once in a 100 year time span. Rather, it is a flood elevation that has a 1% 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
The 100 year flood, which is the standard used by most Federal and State agencies, is used by the National Flood Insurance Program NFIP as the standard for floodplain management and to determine the need for flood insurance.
A structure located in a 100 year floodplain has a 26% chance of suffering flood damage during the term of a 30 year mortgage, and a greater chance of being damaged by a flood than by fire.