Definitions: Flood Zones
Flood Zones
US FEMA assigns flood zones based on their analysis and categorizations. Their Flood Maps are updated and released regularly. Their flood zone definitions are as follows:
| RISK | ZONE | DESCRIPTION |
|---|---|---|
| Higher | A | 100-year Floodplain, areas with a 1% annual chance of flooding. Because detailed analyses are not performed for such areas; no depths or base flood elevations are shown within these zones. |
| Higher | AE, A1-30 | 100-year Floodplain. The base floodplain where base flood elevations are provided. AE Zones are now used on new format FIRMs instead of A1-A30 Zones. |
| Higher | AH | 100-year Floodplain, 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. flood elevations derived from detailed analyses are shown at selected intervals within these zones. |
| Higher | AO | 100-year Floodplain, 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. Average flood depths derived from detailed analyses are shown within these zones. |
| Higher | 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). |
| Higher | A99 | 100-year Floodplain, 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. |
| Lower | X (unspecified) | Outside the limits of the 100-year Floodplain, area with greater than 1% (or 1 in 100 chance) annual chance of flooding. |
| Lower | B and X (shaded) | Between the limits of the 100-year and 500-year Floodplain, area with a 0.2% (or 1 in 500 chance) annual chance of flooding. This zone is also used to designate base flood plains of lesser hazards, such as areas protected by levees from 100-year floods |
| Lower | C and X (unshaded) | 500-year Floodplain, area of minimal flood hazard. |
| Undetermined | D | Areas with possible but undetermined flood hazards. No flood hazard analysis |
Flood Map Coloring
These Flood zones are also available as a map layer. Many differently colored layers area available, but the most common layers are:
| RISK | ZONE | COLOR |
|---|---|---|
| Lower | X | Green |
| Higher | A, AE | Gold |
| Higher | AH | Maroon |
What is base flood elevation?
Base flood elevation (BFE) is the level that surface water will likely reach during a base flood. “Base flood” refers to a flood that has a 1% chance of being either equaled or exceeded in a given area in a given year.
BFE Meaning
Put another way, a BFE shows how high water may rise during a 100-year flood (i.e., a flood that has a 1% chance of happening in any given year). The height of flood waters during a flood may affect insurance rates and coverage.
What is Storm Surge Inundation?
An alternative method of looking at flood risk is based on the severity of a storm and the likelihood and severity of a storm surge caused by each category of storm. In some cases, the National Weather Service can provide projections of what level storm could cause flooding in an area. In case where it can be determined, we will include a red note, with a description of the Projected Storm Category that is likely to cause flooding for a certain property.
NOTE: All flood projections are based on modelling of likelihood of events and conditions as made by their respective agencies and are presented for informational purposes only. Specific conditions change and outlier events are possible beyond the expectations of these projections. PropertyKey is not responsible for any errors or events outside of our control.