Definitions of FEMA Flood Zone Designations
Flood zones are geographic areas that the FEMA has defined according
to varying levels of flood risk.
These zones are depicted on a community’s Flood Insurance Rate Map (FIRM)
or Flood Hazard Boundary Map.
Each zone reflects the severity or type of flooding in the area.
=1= Moderate to Low Risk Areas
In communities that participate in the NFIP, flood insurance is available
to all property owners and renters in these zones:
ZONE DESCRIPTION
B and X (shaded) Area of moderate flood hazard, usually the area between the
limits of the 100-year and 500-year floods. Older maps printed on paper show this zone as shaded in grey. Newer maps shown on there internet show this zone in different colors.
B Zones are also used to designate base floodplains of lesser hazards,
such as areas protected by levees from 100-year flood,
or shallow flooding areas with average depths of less than
one foot or drainage areas less than 1 square mile.
C and X (unshaded) Area of minimal flood hazard, usually depicted on FIRMs
as above the 500-year flood level.
Zone C may have ponding and local drainage problems that don’t
warrant a detailed study or designation as base floodplain.
Zone X is the area determined to be outside the 500-year flood
and can in some cases be protected by a levee in 100-year flood.
=2= High Risk Areas
In communities that participate in the NFIP, flood insurance is available
to all property owners and renters in these zones:
ZONE DESCRIPTION
A Areas with a 1% annual chance of flooding and a 26% chance of
flooding over the life of a 30-year mortgage.
Because detailed analyses are not performed for such areas;
no depths or Base Flood elevations are shown within these zones.
AE The base floodplain where Base Flood elevations are provided.
AE Zones are now used on new format FIRMs instead of A1-A30 Zones.
A1-30 These are known as numbered A Zones (e.g., A7 or A14). This is the base floodplain
where the FIRM shows a BFE (old format).
AH Areas with a 1% annual chance of shallow flooding, usually in the form of a pond,
with an average depth ranging from 1 to 3 feet. These areas have a 26% chance of flooding
over the life of a 30-year mortgage. Base flood elevations derived from detailed analyses
are shown at selected intervals within these zones.
AO River or stream flood hazard areas, and areas with a 1% or greater chance of shallow flooding each year, usually in the form of sheet flow with average depth ranging from 1 to 3 feet. These areas have a 26% chance of flooding over the life of
a 30-year mortgage. Average flood depths derived from detailed
analyses are shown within these zones.
AR Areas with a temporarily increased flood risk due to the building or restoration
of a flood control system (such as a levee or a dam)
Mandatory flood insurance purchase requirements will apply, but rates will not exceed the rates for unnumbered A zones if the structure is built or restored in compliance with Zone AR floodplain management regulations.
A99 Areas with a 1% annual chance of flooding that will be protected by a Federal
flood control system where construction has reached specified legal requirements.
No depths or Base Flood elevations are shown within these zones.
=3= High Risk – Coastal Areas
In communities that participate in the NFIP, flood insurance is available
to all property owners and renters in these zones:
ZONE DESCRIPTION
V Coastal areas with a 1% or greater chance of flooding and an additional
hazard associated with storm waves. These areas have a 26% chance of flooding
over the life of a 30-year mortgage. No Base Flood elevations are shown within these zones.
VE, V1 – 30 Coastal areas with a 1% or greater chance of flooding and an additional
hazard associated with storm waves. These areas have a 26% chance of flooding over
the life of a 30-year mortgage. Base flood elevations derived from detailed analyses are shown at selected intervals within these zones.
Floodway is the the channel of the river or stream and the adjacent land that must remain free from obstruction so that the 100-year flood can be conveyed downstream. A detailed description along with drawings of a floodway regulation is found here .
=4= Undetermined Risk Areas
ZONE DESCRIPTION
D Areas with possible but undetermined flood hazards. No flood hazard analysis has been conducted. Flood insurance rates are commensurate with the uncertainty of the flood risk.
Sources:
FEMA – 2010 as cited on Sept. 22, 2019 at https://fris.nc.gov/fris/metadata/FloodZonesAE.htm
Minnesota Department of Natural Resources
http://files.dnr.state.mn.us/publications/waters/floodplain_management_fact_sheet_2.pdf