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Floodplain definitions
- Flood Zone
- Flood Zones- X, AE, A, AO, VE, Floodway, X(5), D, AH
- 100 Year Flood
- Special Flood Hazard Area
- Base Flood Elevation
Flood Zone - A designation assigned by FEMA defining the various flooding characteristics of different lands based on a 100-year storm. All lands are given a Flood Zone designation, but the term Flood Zone is somewhat misleading. Some Flood Zones (e.g. X and X(5)) are not expected to extensively flood during a 100-year storm. This does not imply that any referenced property will or will not be free from flooding or damage. A property not in a SFHA may be damaged by a flood greater than that predicted on the FIRM or from a local drainage problem not shown on the map. This does not create liability on the part of the County, or any officer or employee thereof, for any damage that results from reliance on this information.
X - areas outside the 100-year floodplain or SFHA, areas of 100-year sheet flow flooding where average depths are less than one foot, areas of 100-year stream flooding where the contributing drainage area is less than one square mile, or areas protected from the 100-year flood by levees. No Base Flood Elevations or depths are shown within this zone. Flood insurance is not mandatory and will be issued at preferred rates. FEMA Elevation Certificates are not required for construction within these areas.
AE - areas within the 100-year floodplain or SFHA, and the Base Flood Elevations have been established. Flood insurance is mandatory. FEMA Elevation Certificates are required for construction within these areas. A FEMA Elevation Certificate is required at the time the floor slab is complete, and one is required at the time of final construction.
A - areas within the 100-year floodplain or SFHA, but the Base Flood Elevations have not been established. Flood insurance is mandatory. FEMA Elevation Certificates are required for construction within these areas. A FEMA Elevation Certificate is required at the time the floor slab is complete, and one is required at the time of final construction.
AO - areas of relatively shallow flooding within the 100-year floodplain or SFHA. No Base Flood Elevations have been established, but a depth of flooding from one to three feet has. Most AO Flood Zones within Jacksonville are designated to flood two feet. Flood insurance is mandatory. FEMA Elevation Certificates are required for construction within these areas. A FEMA Elevation Certificate is required at the time the floor slab is complete, and one is required at the time of final construction.
VE - areas within the 100-year coastal floodplain or SFHA that also have additional hazards associated with storm waves. Base Flood Elevations have been established. Flood insurance is mandatory. Prior to approval of construction within a VE zone, the developer must demonstrate that any structures built will be able to withstand the wave action. FEMA Elevation Certificates are required for construction within these areas. A FEMA Elevation Certificate is required at the time the floor slab is complete, and one is required at the time of final construction.
Floodway - areas within the 100-year floodplain or SFHA that should be left in tact. Construction and filling within these areas is severely restricted. Base Flood Elevations have been established. If construction is allowed within a Floodway, flood insurance will be mandatory. A No-rise Certification and FEMA Elevation Certificates are required for construction within these areas. The No-rise Certification is required prior to construction, a FEMA Elevation Certificate is required at the time the floor slab is complete, and a FEMA Elevation Certificate is required at the time of final construction.
X(5) - areas outside the 100-year floodplain or SFHA but within the 500-year floodplain. Base Flood Elevations have not bee established, and flood insurance is not mandatory. FEMA Elevation Certificates are not required for construction within these areas.
D - areas where there are possible but undetermined flood hazards. In areas designated as Zone D, no analysis of flood hazards has been conducted. Flood insurance is not mandatory, but coverage is available. The flood insurance rates for properties in Zone D are commensurate with the uncertainty of the flood risk. Construction within these areas is evaluated on a case by case basis.
AH - areas of 100-year shallow flooding with a constant water-surface elevation (usually areas of ponding) where average depths are between 1 and 3 feet. The Base Flood Elevations derived from the detailed hydraulic analyses are shown at selected intervals within this zone. Flood insurance is mandatory. FEMA Elevation Certificates are required for construction within these areas. A FEMA Elevation Certificate is required at the time the floor slab is complete, and one is required at the time of final construction.
100-year flood - a flood occurring from a storm event that happens an average of every one-hundred years. This does not mean that a storm of this type will happen every one-hundred years and only every one-hundred years. There is a 1% chance that a storm of this magnitude will occur in any given year. According to the City of Jacksonville's 2010 Comprehensive Plan, a 100-year storm roughly equates to a Category 3 Hurricane.
Special Flood Hazard Area - an area of land that, in the opinion of FEMA, would be inundated by a 100-year flood.
Base Flood Elevation - the height in feet that the 100-year flood is expected to rise above sea level. Elevations are based on National Geodetic Vertical Datum of 1929 or North American Vertical Datum 1988.
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