FEMA Flood Zones
How to Interpret the FEMA FIRM Rate Maps
Whatever the area shown on a FEMA FIRM map, it may include several types of floodplain zones, each designated by a letter or a combination of a letter and number(s). Please see the table below for explanations of these zones.
|The 100-year or base floodplain. Six types of 'A' zones are described below.
|Base flood elevations (BFE) are not determined. This is often called an unnumbered A Zone or an approximate A zone.
|Known as numbered A Zones (e.g., A7 or A14). BFEs are shown on a FEMA map that includes any of these zones.
|On newer FIRMs, AE Zones are the same as A1-A30 Zones (i.e., BFEs are shown).
|The base floodplain with sheet flow, ponding or shallow flooding. Base flood depths (feet above ground) are provided.
|Shallow-flooding base floodplain. BFEs are provided.
|Area to be protected from base flood by levees or Federal Flood Protection Systems under construction. BFEs are not determined.
|The base floodplain that results from the decertification of a previously accredited flood protection system that is in the process of being restored to provide a 100-year or greater level of flood protection.
|The coastal area subject to a velocity hazard (wave action) where BFEs are not determined on the FIRM map.
|The coastal area subject to a velocity hazard (wave action) where BFEs are provided on the FIRM map.
|Zone B and Zone X
|Area of moderate flood hazard, usually the area between the limits of the 100-year and 500-year floods. B Zones are also used to designate base floodplains of lesser hazards, such as areas protected by levees from the 100-year flood, or shallow-flooding areas with average depths of less than one foot or drainage areas less than 1 square mile.
|Zone C and Zone 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 protected by levee from the 100-year flood.
|Area of undetermined but possible flood hazards.