The FEMA (Federal Emergency Management Agency) prepares Flood Insurance Rate Maps (FIRMS) that depict the extent
of Special Flood Hazard Areas (SFHAS) and other thematic features related to flood risk assessment. SFHAs are areas
subject to inundation by a flood having a one- percent or greater probability of being equaled or exceeded during
any given year (this is also known as a 100-year flood event). This flood, which is referred to as the base flood,
is the national standard on which the floodplain management and insurance requirements of the NFIP (National Flood
Insurance Program) are based. The mandatory flood insurance purchase requirements of the 1973 National Flood Insurance
Act apply only when a structure is located in an SFHA in a community that is participating in the NFIP. Such a
structure is required to be insurable by the NFIP under their rules. Even though a portion of the land parcel upon
which the structure is planned or built may be within an SFHA, the mandatory purchase of flood insurance is triggered
only if the structure itself is within an SFHA.
The FIRMs delineate areas of low flood risk (outside the 500-year floodplain) and areas of higher risk. Areas of
higher risk are further delineated into areas of different risk levels. These different areas of risk may be known
by different designations, but the descriptions of the SFHA's include the following:
Special Flood Hazard Areas
Zone A
No base flood elevations determined.
Zone AE
Base flood elevations determined.
Zone AH
Flood depths of I to 3 feet (usually areas of pending); base flood elevations determined.
Zone AO
Flood depths of 1 to 3 feet (usually sheet flow on sloping terrain); average depths determined. For areas of alluvial
fan flooding, velocities also determined.
Zone A99
To be protected from 100-year flood by Federal flood protection system under construction; no base flood elevations
determined.
Special Flood Hazard Areas in Coastal Areas
Zone V
Coastal flood with velocity hazard (wave action); no base flood elevations determined.
Zone VIE
Coastal flood with velocity hazard (wave action); base flood elevations determined.
Other areas
(shaded) Zone X
Areas of 500-year flood; areas of 100-year flood with average depths less than I foot or with drainage areas less
than I square mile; and areas protected by levees from 100-year flood.
(unshaded) Zone X
Areas determined to be outside the 500-year floodplain.
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