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<br />Chapter 1
<br />Introduction
<br />
<br />This Guide has been designed to provide
<br />community officials, planners, and engineers
<br />with information about how to request changes
<br />to National Flood Insurance Program (NFIP)
<br />maps and other flood risk information prepared
<br />by the Federal Emergency Management Agency
<br />(FEMA),
<br />
<br />In the past, FEMA has expended a great deal of
<br />time and effort to obtain the technical
<br />information needed to evaluate requests for
<br />changes to NFIP maps, The goal of this Guide is
<br />to provide general information about the types
<br />of supporting data that FEMA needs to review
<br />and evaluate such requests, Background
<br />information about the NFIP, including the
<br />regulations and procedures under which
<br />requests for changes are handled by FEMA, has
<br />also been provided herei n,
<br />
<br />National Flood Insurance Program
<br />
<br />The U,S, Congress established the NFIP in 196B,
<br />Communities participating in the NFIP do so in
<br />two phases--the Emergency and Regular Phases,
<br />In communities participating in the initial phase
<br />of the NFIP, the Emergency Phase, limited
<br />amounts of flood insurance are available to local
<br />property owners, In communities participating
<br />in the Regular Phase, full flood insurance
<br />coverage is available, The NFIP and related
<br />regulations, which define responsibilities and
<br />requirements for both FEMA and each
<br />participating community, are set forth at Title
<br />44, Chapter I, Parts 59-77, Code of Federal
<br />Regulations (CFR),
<br />
<br />The NFIP was designed to benefit both
<br />individual property owners and communities, It
<br />enables property owners to purchase flood
<br />insurance at reasonable rates, and it assists
<br />communities by requiring that they adopt and
<br />administer local floodplain management
<br />measures aimed at protecting lives and new
<br />construction from future flooding, All
<br />communities that have the authority to adopt,
<br />administer, and enforce floodplain
<br />
<br />management regulations can participate in the
<br />NFIP,
<br />
<br />Under the Emergency Phase of the NFIP, FEMA
<br />issued Flood Hazard Boundary Maps (FHBMs) for
<br />more than 19,000 flood-prone communities in
<br />the United States, FHBMs provide approximate
<br />delineations of areas subject to inundation by
<br />the base (100-year) flood; in the NFIP, these
<br />areas are known as Special Flood Hazard Areas
<br />(SFHAs), The base flood is the flood that has a
<br />l-percent probability of being equaled or
<br />exceeded in any given year and has been
<br />adopted as a regulatory standard by Federal
<br />agencies, and most States, for use in the
<br />administration of floodplain management
<br />programs,
<br />
<br />The boundaries ofthe SFHAs (referred to as 100-
<br />year floodplain boundaries) shown on an FHBM
<br />are based on one or more of the following:
<br />information about past floods, regional flood
<br />depth/drainage area relationships, floodplain
<br />maps published by other Federal agencies, and
<br />simplified hydrologic and hydraulic calculations,
<br />Detailed analyses and field surveys are generally
<br />not performed for the preparation of an FHBM,
<br />As a result, the floodplain boundaries shown are
<br />considered approximate, and the SFHAs are
<br />designated" Zone A,"
<br />
<br />Generally, at some point after an FHBM has been
<br />issued for a community, a detailed engineering
<br />study of the flood hazards in that community--a
<br />Flood Insurance Study (FIS)--is conducted, The
<br />purpose of the FIS is to refine the 1 DO-year
<br />floodplain boundaries shown on the FHBM and
<br />to develop new, detailed flood risk information,
<br />That information usually consists of base flood
<br />elevations (BFEs), which may be presented as
<br />either water-surface elevations referenced to
<br />the National Geodetic Vertical Datum of 1929
<br />(NGVD) or average depths of flow in feet above
<br />the ground surface; 10-, 50-, and SOD-year
<br />water-surface elevations; 100-year floodway
<br />boundaries; and SOD-year floodplain
<br />boundaries, The results of the FIS are presented
<br />on a Flood Insurance Rate Map (FI RM) and,
<br />usually, in an FIS report,
<br />
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