Coastal Construction Manual - National Ready Mixed Concrete ...

IDENTIFYING HAZARDS 3
A USACE Engineering Circular (USACE 2009a) provides guidance on sources of sea level change data and
projections, and discusses how the data and projections can be used for planning purposes. The guidance is
useful for planning and designing coastal residential buildings.
3.7.2 Updating or Revising Flood Hazard Assessments
Updating or revising an existing flood hazard assessment—
for siting and design purposes—can be fairly simple or highly
complex, depending upon the situation. A simple change may
involve shifting a Zone A or Zone X boundary, based upon
topographic data that is better than those used to generate
the FIRM. A complex change may involve a detailed erosion
assessment and significant changes to mapped flood hazard
zones.
If an assessment requires recalculating local flood depths and
wave conditions on a site, FEMA models (Erosion, Runup,
and WHAFIS) can be used for the site (bearing in mind the
recommended change to the required dune reservoir to prevent
dune loss, described in 3.5.8).
NOTE
Coastal hazard analysis models
(Erosion, Runup, WHAFIS) used
by FEMA’s FIS contractors are
available for use by others.
However, those performing
updates or revising flood hazard
assessments are advised to
obtain the assistance of an
experienced coastal professional.
FEMA has also issued its Coastal
Hazard Modeling Program
(CHAMP) to facilitate the use of
standard FEMA models for flood
hazard mapping.
If an assessment requires careful consideration of shore erosion,
the checklist, flowchart, and diagram shown in Chapter 4 can be
a guide, but a qualified coastal professional should be consulted.
Much of the information and analyses described in the checklist and flowchart is likely to have already been
developed and carried out previously by others, and should be available in reports about the area; designers
are advised to check with the community. Cases for which information is unavailable and basic analyses have
not been completed are rare.
The final result of the assessment should be a determination of the greatest flood hazards resulting from a
1-percent-annual-chance coastal flood event that the site will be exposed to over the anticipated life of a
building or development. The determination should account for short- and long-term erosion, bluff stability,
sea level rise, and storm-induced erosion; in other words, both chronic and catastrophic flood and erosion
hazards, along with future water level conditions, should be considered.
3.8 Milestones of FEMA Coastal Flood Hazard Mapping Procedures
and FIRMs
Designers are reminded that FEMA’s flood hazard mapping procedures have evolved over the years (the
coastal mapping site, http://www.fema.gov/plan/prevent/fhm/dl_vzn.shtm, provides links to current coastal
mapping guidance and highlights many of these changes). Thus, a FIRM produced today might differ from
an earlier FIRM, not only because of physical changes at the site, but also because of changes in FEMA
hazard zone definitions, revised models, and updated storm data. Major milestones in the evolution of
FEMA flood hazard mapping procedures, which can render early FIRMs obsolete, include:
COASTAL CONSTRUCTION MANUAL
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