Levees, Dams, and Flood Zones
Levees and dams can reduce flood risk, but they do not eliminate it. Whether a flood control structure protects your property on FEMA's maps depends on its accreditation status and structural condition.
Last updated: August 2026
How Levees Affect Flood Zones
A levee is a man-made structure or engineered fill designed to prevent floodwater from reaching the area behind it. Levees are built along rivers, channels, and coastlines. On FEMA flood maps, the flood zone designation for the area behind a levee depends entirely on whether the levee meets FEMA's accreditation standards.
Accredited Levee
If a levee meets FEMA's accreditation standards under 44 CFR 65.10, the area behind it may be mapped as Zone X (outside the SFHA). This means flood insurance is not required by federal law, though it is still recommended.
Provisionally Accredited (PAL)
A third status between the two: the levee owner has signed an agreement to submit full 44 CFR 65.10 data within a set timeframe (generally up to 24 months). The area stays mapped in the SFHA and insurance is still required while the PAL is in effect - it signals accreditation is in progress, not that it has been granted.
Unaccredited Levee
If a levee does not meet FEMA's standards or has lost its accreditation, the area behind it remains mapped in the SFHA (typically Zone AE). Flood insurance is required for federally-backed mortgages, and the levee is treated as if it does not exist for mapping purposes.
FEMA does not own, maintain, or set construction standards for levees. The agency only determines whether a levee meets the criteria to be recognized on the flood map. Levee maintenance and certification are the responsibility of the levee owner (typically a local levee district, municipality, or the US Army Corps of Engineers) - a separate track from the federal repair funding program covered below.
Levee Accreditation Requirements (44 CFR 65.10)
To be recognized by FEMA on a flood map, a levee must meet all of the following accreditation requirements under 44 CFR 65.10:
- The levee must provide adequate freeboard - additional height above the base flood elevation that provides a safety margin. For a riverine levee, that means at least 3 feet above the 1% annual chance flood elevation. Coastal levees use a different formula: at least 1 foot above the 1% annual chance wave height or wave runup elevation, with an absolute floor of 2 feet above the stillwater surge elevation.
- All openings in the levee (such as gates, pumping stations, and roadway crossings) must have certified closure devices that can be operated in time to prevent floodwater from passing through.
- The levee embankments and foundations must be certified by a professional engineer as resistant to erosion, seepage, settlement, and structural instability under flood conditions.
- The levee must be certified against future loss of freeboard due to settlement of the embankment or foundation materials.
- The levee must have an active operation and maintenance plan, and the responsible entity must demonstrate the capacity to carry it out.
A levee that was once accredited can lose its status if the responsible entity fails to maintain it, if the levee settles below the required freeboard, or if a new study reveals it does not meet the standards. When this happens, FEMA remaps the area behind the levee back into the SFHA.
PL 84-99: Federal Levee Rehabilitation Funding
Separately from FEMA accreditation, the US Army Corps of Engineers runs the Rehabilitation and Inspection Program, authorized under Public Law 84-99. It is a disaster-repair funding track, not a flood zone mapping determination - a levee's PL 84-99 status has no direct effect on whether its area is mapped in the SFHA.
- Active systems are enrolled and eligible for federal cost-share (in some cases full federal funding) to repair storm damage, provided they pass USACE's recurring inspections.
- Inactive systems have voluntarily left the program or failed an inspection, and are not eligible for federal repair funding until they regain Active status through a new inspection.
- Not Enrolled systems were never part of the program - typically levees built and maintained entirely by a local sponsor with no USACE involvement.
A levee can be FEMA-accredited and PL 84-99 Active, accredited and not enrolled, non-accredited and Active, or any other combination - the two systems are run by different agencies for different purposes. FludZone's city pages show a levee system's PL 84-99 rehabilitation status alongside its FEMA accreditation where both are known.
Zone AR: Levees Under Restoration
Zone AR is a special SFHA designation for areas that were previously protected by a levee or flood control system that has been decertified and is actively being restored. Zone AR acknowledges that the area is temporarily at higher risk while the restoration project is underway.
Zone AR has a concrete deadline, not an open-ended one. Federally funded restoration projects have up to 10 years to complete the work; non-federally funded projects have up to 5 years. The community must certify "adequate progress" to FEMA every year the restoration is underway. If that window closes without adequate progress, FEMA remaps the area using standard non-accredited procedures rather than extending the AR designation indefinitely.
Once the levee is restored and re-accredited, FEMA remaps the area behind it, typically moving it back out of the SFHA. During the AR designation period, flood insurance is required for federally-backed mortgages, but specific rating provisions apply.
Zone A99: New Federal Flood Control Systems
Zone A99 is easy to confuse with Zone AR, but it covers the opposite situation. AR applies where an existing levee lost its accreditation and is being restored. A99 applies where a new federal flood control system is under construction and has not been accredited yet - there was no prior accreditation to lose.
FEMA only applies the A99 designation once a project has met statutory progress thresholds toward completion, and no Base Flood Elevation is shown for A99 areas. Like AR, properties in Zone A99 are in the SFHA and flood insurance is required for federally-backed mortgages until the system is complete and accredited.
How Dams Affect Flood Zones
Dams are built across watercourses to impound water for flood control, water supply, hydropower, recreation, or other purposes. The Flood Insurance Study (FIS) for your community documents any dams that affect flood flows in the study area, including their type, dimensions, purpose, and historical performance.
Dams can reduce downstream flood flows by retaining and slowly releasing floodwater. If a dam provides recognized flood protection, the downstream area may be mapped in a lower-risk zone. However, dams also introduce a risk that is not shown on FEMA flood maps: dam failure.
FEMA flood maps do not show dam failure inundation zones. Dam failure mapping is maintained by dam owners and state dam safety programs, not the NFIP. If you live downstream of a dam, contact your state dam safety office for information about potential inundation areas and emergency action plans.
Do I Need Flood Insurance If I Live Behind a Levee?
Even when a levee is accredited or a dam provides recognized flood protection, residual flood risk remains. No flood control structure provides absolute protection.
- Floods larger than the design event can overtop a levee or exceed a dam's capacity. An accredited levee provides 3 feet of freeboard above the base flood, but a more extreme event could exceed that margin.
- Levees and dams can fail due to erosion, seepage, foundation problems, or lack of maintenance. Failure can happen during a flood or even under normal conditions.
- Even when a levee holds, rainfall on the protected side can cause interior flooding if the pumping or drainage systems cannot keep up.
- Properties behind levees often have lower rates of flood insurance, which means residents face greater financial exposure if the levee fails or is overtopped.
FEMA and the US Army Corps of Engineers recommend that property owners behind levees maintain flood insurance even when it is not required. The cost of a Zone X policy is relatively low, and it provides financial protection against events that exceed the levee's design capacity.
Frequently Asked Questions
Does living behind a levee mean I am not in a flood zone?
Not necessarily. If the levee is FEMA-accredited under 44 CFR 65.10, the area behind it may be mapped outside the SFHA. If the levee is unaccredited, the area behind it remains in the SFHA and flood insurance is still required for federally-backed mortgages.
What does it mean for a levee to be FEMA-accredited?
FEMA accreditation under 44 CFR 65.10 requires that a levee provide at least 3 feet of freeboard above the 1% annual chance flood, have certified closure devices at all openings, and have embankments and foundations certified against erosion, seepage, and instability.
Are dam failure flood zones shown on FEMA flood maps?
No. FEMA flood maps do not show dam failure inundation zones. Dam failure mapping is maintained by dam owners and state dam safety programs, not the NFIP. Contact your state dam safety office for information about dam inundation zones in your area.
What is a Provisionally Accredited Levee (PAL)?
A Provisionally Accredited Levee is a third status between accredited and non-accredited. FEMA assigns it when a levee owner has signed an agreement committing to submit the full data required under 44 CFR 65.10 within a set timeframe, generally up to 24 months. A PAL area is still mapped in the SFHA and flood insurance is still required, but the designation signals accreditation is actively in progress rather than absent.
How long can an area stay in Zone AR before it must be remapped?
Federally funded levee restoration projects have up to 10 years to complete the work; non-federally funded projects have up to 5 years. The community must certify "adequate progress" to FEMA annually. If the timeframe expires without adequate progress, FEMA remaps the area using standard non-accredited procedures rather than keeping the AR designation indefinitely.
Related Resources
The high-risk zone you may be in if your levee is unaccredited.
How levee accreditation changes trigger map revisions.
Insurance guidance based on your flood zone and levee status.
Where dam and levee data is documented in FEMA studies.
See levee systems, accreditation status, and rehabilitation status for over 1,300 US cities.
Sources
- FEMA Flood Maps (opens in new tab)General Reference
Explore Flood Zones by State
Check flood zone information for cities across the United States.
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