Coastal Construction Manual - National Ready Mixed Concrete ...

3 IDENTIFYING HAZARDS
Zones X, B, and C. These zones identify areas outside the SFHA. Zone B and shaded Zone X-500 identify
areas subject to inundation by the flood that has a 0.2-percent chance of being equaled or exceeded during
any given year, often referred to as the 500-year flood. Zone C and unshaded Zone X identify areas outside
the 500-year floodplain. Areas protected by accredited levee systems are mapped as shaded Zone X.
TERMINOLOGY
SPECIAL FLOOD HAZARD AREA (SFHA) defines an area with a 1-percent chance, or greater, of
flooding in any given year. This is commonly referred to as the extent of the 100-year floodplain.
COASTAL SFHA is the portion of the SFHA where the source of flooding is coastal surge or
inundation. It includes Zone VE and Coastal A Zone.
ZONE VE is that portion of the coastal SFHA where base flood wave heights are 3 feet or greater, or
where other damaging base flood wave effects have been identified, or where the primary frontal dune
has been identified.
COASTAL A ZONE (MoWA AREA) is that portion of the coastal SFHA referenced by building
codes and standards, where base flood wave heights are between 1.5 and 3 feet, and where wave
characteristics are deemed sufficient to damage many NFIP-compliant structures on shallow or solid wall
foundations.
MiWA AREA is that portion of the Coastal SFHA where base flood wave heights are less than 1.5 feet.
LiMWA is the boundary between the MoWA and the MiWA.
RIVERINE SFHA is that portion of the SFHA mapped as Zone AE and where the source of flooding is
riverine, not coastal.
ZONE AE is the portion of the SFHA not mapped as Zone VE. It includes the MoWA, the MiWA, and the
Riverine SFHA.
3.6.3 FIRMs, DFIRMs, and FISs
Figure 3-52 shows a typical paper FIRM that a designer might
encounter for some coastal areas. Three flood hazard zones are
shown on this FIRM: Zone V, Zone A, and Zone X. Figure 3-53
shows an example of a transect perpendicular to the shoreline.
Since the early 2000s, FEMA has been preparing Digital FIRMs
(DFIRMs) to replace the paper maps. Figure 3-54 shows a typical
DFIRM that a designer is likely to encounter in many coastal areas.
The DFIRM uses a photographic base and shows either the results
of a recent FIS or the results of a digitized paper FIRM (possibly
with a datum conversion from National Geodetic Vertical Datum
[NGVD] to North American Vertical Datum [NAVD]). The flood
hazard zones and BFEs on a DFIRM are delineated in a manner
consistent with those on a paper FIRM, although they may reflect
updated flood hazard calculation procedures.
CROSS REFERENCE
See Section 3.3 for a brief
discussion of coastal flood
hazards and FIRMs.
NOTE
Additional information about
FIRMs is available in FEMA’s
2006 booklet How to Use a
Flood Map to Protect Your
Property, FEMA 258 (FEMA
2006b).
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