FEMA Flood Hazard FIRM Maps
FIRM Floodplain Maps
Definition & Purpose
Flood Insurance Rate Maps (FIRMs) are official maps on which the Federal Emergency Management Agency (FEMA) has delineated flood hazard areas and risk zones. They show the location of a property relative to flood hazard areas, which is one of the factors used to calculate flood insurance rates. More information on FIRMs is available at the FloodSmart.gov website or visit the FEMA Flood Map Service Center.
FIRMs are use by:
- Homeowners, insurance agents, and real estate brokers to determine if a specific property or building is in a flood hazard area;
- Planning staff and building officials to administer floodplain management regulations and to mitigate flood damage; and
- Lending institutions and federal agencies to locate properties and building in relation to mapped flood hazards, and to determine if flood insurance is required when making loans for the purchase or construction of a building or for providing grants after a disaster.
Definitions of FEMA Flood Zone Designations
Flood zones are geographical 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.
Moderate to Low Risk Areas
In communities that participate in the National Flood Insurance Program (NFIP), flood insurance is available to all property owners and renters in these zones:
|B and X (shaded)||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 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 protected by levee from 100-year flood.|
High Risk Areas
In communities that participate in the NFIP, mandatory flood insurance purchase requirements apply to all of these zones:
|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 analysis 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 A10-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 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 analysis 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 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. 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.|
High Risk - Coastal Areas
In communities that participated in the NFIP, mandatory flood insurance purchase requirements apply to all of these zones.
|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.|
Undetermined Risk Areas
|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.|
The City received updated Digital Flood Insurance Rate Maps from Snohomish County and FEMA. The maps were adopted by the City of Arlington in June 2020.