New Coastal Flood Risk
Information – Limit of
Moderate Wave Action
The Federal Emergency Management Agency (FEMA) Region IV Office in
Atlanta has undertaken a multiyear coastal engineering analysis and
mapping effort to better identify, quantify, and communicate flood hazards
and associated risks in coastal communities in the Southeastern United
States. As part of this effort, FEMA is producing updated Flood Insurance
Rate Maps (FIRMs) and Flood Insurance Study (FIS) reports for affected
communities.
In addition to the regulatory mappinng elements shown on new and updated
FIRMs—Special Flood Hazard Areas, which are areas that would be
inundated by the base (1-percent-annual-chance) flood, and Base Flood
Elevations)—FEMA provides an informational layer for the Limit of
Moderate Wave Action, or LiMWA. The purpose of this Fact Sheet is to
explain how and why FEMA depicts the LiMWA on the updated FIRMs.
Background on Coastal Zones
FEMA uses two different flood insurance risk zones to identify areas
affected by coastal flood hazards:
 Zone VE, where the delineated flood hazard identifies areas exposed to
wave heights that are 3 feet or higher. These areas are also referred to
as Coastal High Hazard Areas, or CHHAs.
 Zone AE, where the delineated flood hazard identifies areas that are
subject to wave heights less than 3 feet.
Post-storm field visits and laboratory tests have confirmed that wave heights
as low as 1.5 feet can cause significant structural damage to buildings when
constructed without consideration to coastal hazards. Additional flood
hazards associated with coastal waves – floating debris, high-velocity flow,
erosion, and scour – can cause structural damage in these areas unless they
were built to VE Zone standards.
To inform communities of the potential for significant wave damage on the
updated FIRMs, FEMA maps the LiMWA, which is the limit of the 1.5-foot
wave. The area between the LiMWA and the CHHA is referred to as the
Coastal A Zone. See Figure 1.
August 2016
LiMWA Quick Facts
 Waves of 1.5 feet or higher have been
determined to cause significant
damage to the structures with which
they come in contact.
 FEMA is showing a Limit of Moderate
Wave Action (LiMWA) line, which
identifies the limit of the 1.5-foot wave,
on FIRMs produced along the coast of
the Southeastern U.S., where
applicable.
 Although the LiMWA is frequently
used to enforce Zone VE building
code standards in the Coastal A Zone,
the LiMWA has no effect on a
structure’s National Flood Insurance
Program flood zone status and,
therefore, does not impact their
Federal flood insurance premium
rates. Property owners are still
encouraged to build higher and insure
themselves with all hazards in mind.
LiMWAs and the Community
Rating System (CRS)
Through the CRS, FEMA provides
credits for communities requiring VE
Zone construction standards in areas
landward of the CHHA and seaward of
the LiMWA line (that is, Coastal A
Zones). Communities that adopt VE
Zone standards and reference the
LiMWA may receive CRS credits, which
could lower insurance premium rates for
affected property owners. For more
information on the CRS, please visit:
www.fema.gov/national-flood-insuranceprogram-community-rating-system.
For More Information
To learn more about the coastal analysis
and mapping effort in the Southeastern
United States, please visit
www.southeastcoastalmaps.com.
A FEMA Fact Sheet is available tor
communities who want to learn more
about how they may use the LiMWA to
implement higher construction
standards
https://www.fema.gov/risk-mapping-assessment-and-planning-risk-map · 1–877–FEMA MAP
Figure 1. Coastal Flood Zones
LiMWA and Coastal A Zone
Mapping
To map the LiMWA, the project team analyzes the wave
transect profile and wave height results generated by the
Wave Height Analysis for Flood Insurance Studies
(WHAFIS) model. Wave height points are evaluated
along each WHAFIS transect to locate where the wave
height exceeds 1.5 feet. Transects are cross sections
taken perpendicular to the shoreline that represent
segments of the coast with similar characteristics. Wave
height is the vertical distance between the highest part of
the wave (the wave crest) and the lowest part of the
wave (the wave trough). Similar to a flood hazard zone
boundary, the LiMWA is connected via interpolation
between transects.
Once the coastal flood hazard mapping is complete, FEMA
provides Preliminary versions of the updated FIRMs and
FIS reports to community officials and citizens for their
review and use. An example of what the updated FIRMs
look like with a LiMWA shown is provided in Figure 2.
The FIRMs also include a “Notes to User” section with
additional LiMWA information.
Figure 2. Sample Updated FIRM
CRS Credits
Through the CRS, FEMA encourages sound floodplain
management practices. In the coastal zone, that includes
using LiMWA data to build structures that will
withstand the wave conditions. Communities that require
foundations designed and built to withstand VE Zone
conditions in the Coastal A Zone can earn up to 225
CRS points. Communities can earn up to 650 CRS
points if they regulate all of their flood hazard zones to
VE Zone standards.
Contact Information
Questions regarding the coastal flood risk studies should
be addressed to the community floodplain
administrators, to the State National Flood Insurance
Program Coordinator, or to FEMA Region IV.
Community, State, and FEMA contact information is
accessible through the “Coastal Study Contacts” page on
the FEMA Web Portal located at
www.southeastcoastalmaps.com/Pages/coastal_contacts.as
px.
For more information on the process for releasing the
Preliminary version of the updated FIRMs and FIS reports,
please see the FEMA Coastal Flood Risk Study Meetings
Fact Sheet, which is accessible through the “Coastal Study
Resources” page on the FEMA Web Portal at
www.southeastcoastalmaps.com/Pages/resources.aspx.
August 2016
https://www.fema.gov/risk-mapping-assessment-and-planning-risk-map · 1–877–FEMA MAP