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<br />The Flood Boundary and Floodway Map is generally derived from a <br />detailed hydraulic study and should provide reasonably accurate information. <br />The hydraulic data are available through regional offices of the Federal <br />Emergency Management Agency and are normally in the form of computer <br />input data sets for calculating water surface profiles. The Flood Insurance <br />Rate Map is usually developed at the same time as the water surface profile <br />analysis model and has base flood elevations added. <br /> <br />The analysis of proposed development within the floodplain generally falls <br />within four categories of studies with regard to the NFIP regulations. These <br />are: (1) a detailed flood insurance study has been performed and a regulatory <br />floodway is in effect; (2) a community is participating in the regular program <br />and 100 year flood elevations have been determined, but no regulatory <br />f100dway has been established; and (3) 100 year flood elevations have not <br />been established, but a one hundred year flood plain has been approximated, <br />or (4) an area has not been identified as flood prone. This document focuses <br />primarily on the development proposals and requirements within floodplain <br />boundaries where regulatory floodways are in effect. Section 8 briefly over- <br />views development conditions for conditions 2 and 3. <br /> <br />Errors in topographic maps, delineation of the base flood, and ot! <br />may produce errors in the floodplain delineation on the Flood Bou <br />Floodway Maps. However, these errors do not.affect the profile <br />The procedure for properly determining the limits of the floodpl, <br />relationship to the proposed development location are descrit <br />following paragraphs. <br /> <br />1. The 1 DO-year or base flood profi Ie elevation for the corn <br />proposed development stream mile should be determined from <br />profiles or floodway data tables provided with the FIS report. <br /> <br />2. A field survey of the proposed development site should be COI <br />determine whether the site actually lies outside (above) the flD< <br />within the floodway fringe and floodway area. See Figure 3. This <br />is more accurate than a determination from the Flood Boundary and <br />Map/FIRM. <br /> <br />FLOOD FRINGE <br /> <br />flOODWAY <br /> <br />3. Preliminary Evaluation of Proposed Development <br /> <br />3-1. General. The location in the floodplain of the proposed development <br />has a significant effect on the development requirements. Development <br />outside the floodway fringe areas, or above the elevation of the base flood is <br />generally not governed by the NFIP floodplain regulations. Within ~he <br />flood way fringe, new development or substantial improvements to existing <br />structures are allowed, provided that all residential developments be elevated <br />to or above the base flood level and non-residential development be elevated <br />or floodproofed to or above the base flood level. Development within the <br />regulatory f100dway is only allowed if there is no resulting increase in flood <br />elevations. <br /> <br />3-2. Locating Floodplain Development. An initial step of the developer is <br />to determine the location of the proposed development with respect to the <br />f100dway fringe and floodway delineation for the area. The developer should <br />obtain from the appropriate local officials the base profile and the Flood <br />Boundary and Floodway Map and/or Flood Insurance Rate Map for t~e stream <br />in the vicinity of the proposed development. Once the floodway fringe and <br />floodways are defined accurately, the proposed development location with <br />respect to them can be established. <br /> <br />The base flood elevation or 1 DO-year flood profile is considered to be the <br />basis for the limits of the floodplain. Once the profile elevations at the cross <br />sections are determined, the floodplain boundaries are delineated ~sing <br />topographic maps to relate to the profile elevations between the cross sections. <br /> <br /> <br />Elevation from Base <br />Profile location May <br />Be Established From <br />Field Surveys <br />location Approximated from Sc< <br />Off of Flood l:Joundary and FIOOt <br /> <br />No NFIP <br />Floodplain <br />Criteria <br /> <br />Flood Fringe <br />Development <br />Criteria <br />Base Flood <br />& Freeboard <br /> <br /> <br />Floodway Criteria - No Rise <br /> <br />Figure 3: Development location <br /> <br />3. If the flood maps show the structure or property to bewithin thE <br />fringe, but the field surveys show otherwise the owner may request <br />Map Amendment (LaMA) from FEMA to become exempt from <br />surance purchase requirements. The developer, through the comm <br />also request that FEMA formally revise flood maps through a Leu <br />Revision (LOMr) if it is shown that the original study is in error due t< <br />computations, better analyses, changed conditions, or other factor <br /> <br />4. Floodway limits are less precise and must be scaled off maps I <br />or other physical features relatable from the site and flood bou, <br />floodway maps. The accuracy of determining whether or not a <br />development site is in the floodway fringe or floodway is affed <br />closeness of the site to actual cross sections, physical feature! <br /> <br />6 <br />