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<br />hydraulic analyses and delineate new floodplain boundaries and
<br />flood ways as necessary, In addition, new flooding information can-
<br />not be added to a NFIP map in such a way as to create mis-
<br />matches with the flooding information shown for unrevised areas,
<br />Therefore, in performing new analyses and developing revised
<br />flooding information, the requestor must tie his new flood
<br />elevations, floodplain boundaries, and floodways into those shown
<br />for areas not affected by the revisions, When requests involve new
<br />flood discharge values, extensive changes in hydraulic conditions,
<br />or complex situations in which changes made to the flooding infor-
<br />mation developed for one flooding source will affect that
<br />developed for others, the requestor may be required to provide
<br />new information for a large portion of the map"
<br />. All analyses and data submitted by the requestor must be certified
<br />by a registered professional engineer or licensed land surveyor, as
<br />appropriate,
<br />. Revisions cannot be made based on the effects of proposed proj-
<br />ects or future conditions; therefore, unless a conditional revision is
<br />requested, any maps, plans, drawings, measurements, or elevation
<br />data submitted by the appellant must be certified "as-built" or as
<br />representing existing conditions, additionally, FEMA will not make
<br />revisions to phases of a project. Revisions are made only when the
<br />whole projects is complete,;
<br />. NFIP maps may be revised when flood discharges change as a
<br />result of structural improvements, such as dams or other signifi'
<br />cant retention facilities, However, NFIP maps will not be revised
<br />when discharges change as a result of the use of an alternative
<br />methodology or better data unless the change is statistically
<br />significant. The criteria to be used in determining whether a
<br />change is statistically significant are discussed in Section 2-6,
<br />"Hydrologic Analyses," of the FEMA Guidelines and Specifica-
<br />tions for Study Contractors (dated September 1985), Therefore,
<br />when requesting a revision based on new flood discharges, the
<br />requestor should determine the significance of the change before
<br />proceeding with new hydraulic analyses, When the statistical
<br />significance test does not apply, a determination by a Federal or
<br />State agency that the change is significant may be accepted as
<br />the basis for revision,
<br />. When a requestor is required to submit a hydraulic analysis for
<br />flooding sources originally studied by detailed methods, the
<br />analysis must be performed for the 10" 50" 100-, and 500'year
<br />floods and floodway, Unless the basis of the request is the use of
<br />an alternative hydraulic methodology, the analysis should be made
<br />using the same hydraulic computer model used to deveiop the
<br />BFE's shown on the effective NFIP map, You may request, through
<br />the appropriate FEMA Regional Office, a copy of the input and
<br />output data from the originai computer model. Any differences be'
<br />tween the original and revised models must be justified on the
<br />basis of physical changes that have occurred, better hydraulic
<br />data, or revised discharges, The revised model should also include
<br />all existing conditions, including any encroachments that have
<br />occurred in the floodplain since the original model was developed,
<br />When the new hydraulic analysis is submitted to FEMA, copies of
<br />the input and output data from the original and revised computer
<br />models should be submitted,
<br />. For information concerning additional data that must be submitted
<br />to support requests that involve changes to floodways refer to
<br />FEMA pOlicy concerning floodway revisions in Section I,
<br />Amendments of this document.
<br />. When a requestor is required to submit a hydrologic or hydraulic
<br />analysis for a flooding source originally studied by approximate
<br />methods, the analysis may be performed for only the 100-year
<br />flood,
<br />. When requesting a revision of fioodplain delineations based on
<br />significant topographiC changes, the requestor must verify that the
<br />new topographiC data do not significantly alter the hydraulic
<br />characteristics of the stream; if they do, a new hydraulic analysis
<br />may be necessary,
<br />. When a requestor is required to submit delineations of floodplain
<br />boundaries for a flooding source originally studied by detailed
<br />methods, both the 100-, and 500'year floodplain boundaries must
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