The national standard for floodplain management is the base, or one percent chance flood. This flood has at least one chance in 100 of occurring in any given year. It is also called a 100 year flood.
Also referred to as the 100-year flood, it is a flood having a 1 percent probability of occurring in any given year.
(p) - for any given community or area, the flood that becomes the standard of measurement of a covered occurrence. Specifically, the flood that has a probability of one percent of being either equaled or exceeded.
The flood or tide having a 1 percent chance of being exceeded in any given year (100-year flood). The 'base flood' is commonly used as the 'standard flood' in Federal flood insurance studies. (see Regulatory Flood).