A floodplain is the part of the land where water collects, pools, and flows during stormwater runoff events. Such areas are classified as Special Flood Hazard Areas (SFHA), and are located in a 100-year flood zone.
The term “100-year flood” can be misleading. It is not the flood event which occurs only once in a 100-year time span. Rather, it is a flood discharge that has a 1% chance of being equaled or exceeded each year. The 100-year flood could occur more than once in a relatively short period of time
The 100-year flood zone is used by the National Flood Insurance Program (NFIP) as the standard for floodplain management to determine flood risk. For example, a structure located in a 100-year floodplain has a 26% chance of suffering flood damage during the term of a 30-year mortgage.