FLOOD HAZARD ZONES

W­­­HAT ARE FLOOD HAZARD ZONES AND WHAT DO THEY MEAN?

W­­­HAT ARE FLOOD HAZARD ZONES AND WHAT DO THEY MEAN?

Several areas of flood hazard are commonly identified on the DFIRM and IRM. One of these areas is the SFHA, which is defined as the area that would be inundated by the flood event having a 1 percent chance of being equaled or exceeded in any given year. The 1-percent-annual-chance flood is also referred to as the “base flood.” SFHAs are labeled as Zone A, Zone AO, Zone AH, Zones A1–A30, Zone AE, Zone 99, Zone AR, Zone AR/AE, Zone AR/AH, Zone AR/AO, Zone AR/A1–A30, Zone AR/A, Zone V, Zone VE, and Zones V1–V30. Moderate flood hazard areas, labeled Zone B, are also shown on the FIRM or DFIRM and are the areas between the limits of the base flood and the 0.2-percent-annual-chance flood. The areas of minimal flood hazard, which are the areas outside the SFHA and higher than the elevation of the 0.2-percent-annual-chance flood, are labeled Zone C. On new and revised maps, Zone X is used in place of Zones B and C. An unshaded Zone X holds the same meaning as the labeled Zone B. A shaded Zone X can mean any of the following: the area is in the 0.2 floodplain; is protected by a levee; is subject to inundation by a flood event having a 1 percent chance of reaching less than a 1.0-foot depth; is subject to inundation by a 1-percent-annual chance flood within an area of less than 1 square mile; or is subject to inundation by a 1-percent-annual-chance flood determined using future conditions. The definitions for the various flood hazard areas are below.

Zone V: Primary frontal dunes and areas along coasts subject to inundation by the 1-percent-annual-chance flood event with additional hazards associated with storm-induced waves. Because detailed coastal analyses have not been performed, no BFEs or flood depths are shown. Mandatory flood insurance purchase requirements apply.

Zones VE and V1–V30: Primary frontal dunes and areas along coasts subject to inundation by the 1-percent-annual-chance flood event with additional hazards due to storm-induced velocity wave action. BFEs derived from detailed hydraulic coastal analyses are shown within these zones. Mandatory flood insurance purchase requirements apply. Zone VE is used on new and revised maps in place of Zones V1–V30.

Zone A: Areas subject to inundation by the 1-percent-annual-chance flood event. Because detailed hydraulic analyses have not been performed, no BFEs or flood depths are shown. Mandatory flood insurance purchase requirements apply.

Zones AE and A1–A30: Areas subject to inundation by the 1-percent-annual-chance flood event determined by detailed methods. BFEs 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–A30.)

Zone AH: Areas subject to inundation by 1-percent-annual-chance shallow flooding (usually areas of ponding) where average depths are 1–3 feet. BFEs derived from detailed hydraulic analyses are shown in this zone. Mandatory flood insurance purchase requirements apply.

Zone AO: Areas subject to inundation by 1-percent-annual-chance shallow flooding (usually sheet flow on sloping terrain) where average depths are 1–3 feet. Average flood depths derived from detailed hydraulic analyses are shown within this zone. Mandatory flood insurance purchase requirements apply.

Zone A99: Areas subject to inundation by the 1-percent-annual-chance flood event, but which will ultimately be protected upon completion of an under-construction Federal flood protection system. These are areas of special flood hazard where enough progress has been made on the construction of a protection system, such as dikes, dams, and levees, to consider it complete for insurance rating purposes. Zone A99 may be used only when the flood protection system has reached specified statutory progress toward completion. No BFEs or flood depths are shown. Mandatory flood insurance purchase requirements apply.

Zone AR: Areas that result from the decertification of a previously accredited flood protection system that is determined to be in the process of being restored to provide base flood protection. Mandatory flood insurance purchase requirements apply.

Zones AR/AE, AR/AH, AR/AO, AR/A1–A30, and AR/A: Dual flood zones that, because of the risk of flooding from other water sources that the flood protection system does not contain, will continue to be subject to flooding after the flood protection system is adequately restored. Mandatory flood insurance purchase requirements apply.

Zones B, C, and X: Areas identified in a community’s FIS as areas of moderate or minimal hazard from the principal source of flood in the area. However, buildings in these zones could be flooded by severe, concentrated rainfall coupled with inadequate local drainage systems. Local stormwater drainage systems are not normally considered in a community’s FIS. The failure of a local drainage system creates areas of high flood risk within these rate zones. Flood insurance is available in participating communities but is not required by regulation in these zones. Zone X is used on new and revised maps in place of Zones B and C.

For More information contact:
Burk Cornelius, PLS 
| Sr. Project Manager | Bureau Veritas
p 800-411-2010 x 3326 | burk.cornelius@bvna.com