What are flood hazard zones and what do they mean?

Flood Insurance Rate Map (FIRM)

The Flood Insurance Rate Map (FIRM) shows areas within the 100-year flood boundary, which are termed "Special Flood Hazard Areas (SFHAs)." 

100 Year Flood

A "100 year flood" does not refer to a flood that occurs once every 100 years, but refers to a flood level with a 1% or greater chance of being equaled or exceeded in any given year. The SFHAs may be further subdivided into insurance risk rate zones. Areas between the 100 year and 500 year flood boundaries are termed "moderate flood hazard areas." The remaining areas are above the 500 year flood level and are termed "minimal flood hazard areas."

Historically, about one-third of claims paid by the NFIP are for flood damage tin areas identified as having only "moderate" and "minimal" risk of flood. Flooding in these often is the result of inadequate local drainage 25 systems, and such flooding sources with small drainage areas are generally not identified on FIRMS. 

Flood Hazard Zones

The SFHAs are subdivided into flood hazard zones (insurance risk rate zones) according to the following criteria:

  • Zone A
    • Because detailed hydraulic analyses have not been performed, no base flood elevation or depths are shown
    • Mandatory flood insurance purchase requirements apply
    • SFHAs subject to inundation by the 100 year flood
  • Zones AE:
    • Base flood elevations are shown within these zones
    • Mandatory flood insurance purchase requirements apply (Zone AE is used on new and revised maps in place of Zones A1-30.)
    • SFHAs subject to inundation by the 100 year flood determined in a Flood Insurance Study by detailed methods
  • Zone AH:
    • Base flood elevations derived from detailed hydraulic analyses are shown in this zone
    • Mandatory flood insurance purchase requirements apply
    • SFHAs subject to inundation by 100 year shallow flooding (usually areas of ponding) where average depths are between one and three feet
  • Zone AO:
    • Average flood depths derived from detailed hydraulic analyses are shown within this zone
    • Mandatory flood insurance purchase requirements apply
    • SFHAs subject to inundation by 100 year shallow flooding (usually sheet flow on sloping terrain) where average depths are between one and three feet
  • Zone X:
    • Flood insurance is available in participating communities but is not required by regulation in these zones
    • However, buildings in these zones could be flooded by severe, concentrated rainfall coupled with inadequate local creates areas of high flood risk within these rate zones
    • These areas have been identified in the community flood insurance study as areas of moderate or minimal hazard from the principal source of flood in the area

Show All Answers

1. What is a floodplain?
2. What is a floodway and who designates it?
3. How do I find out if my property is in a floodplain?
4. What are the penalties if I don't secure all my permits?
5. How are premiums calculated?
6. What constitutes as substantial improvement or substantial damage?
7. How are flood hazard areas and flood levels determined?
8. What are flood hazard zones and what do they mean?
9. If a Flood Insurance Rate Map (FIRM) is believed to be incorrect, what can be done to change it?
10. What is Letter Of Map Amendment (LOMA)?
11. What comprises technical or scientific data?
12. What is a Letter Of Map Revision (LOMR)?