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<br />community officials should be aware of specific applicable requirements in <br />order to avoid adverse flood insurance rating. <br /> <br />5-7. Highway Stream Crossing. For communities where the NFIP regula- <br />tions are in effect and the regulatory floodway defined, the initial alternative <br />analyzed should be a highway stream crossing with all components excluded <br />from the floodway. The design, which essentially spans the floodway, must <br />also limit the rise of the base flood (1 DO-year flood profile) within the <br />regulatory criteria (normally one foot). The alternative must be sufficiently <br />detailed to show the effect on the f100dway profile. <br /> <br />when it is clearly shown to be inappropriate to design a highway crossing <br />to avoid encroachment on the floodway and where the floodway cannot be <br />modified such that the structure could be excluded, FEMA will approve an <br />alternate f100dway with profile in excess of the 1 foot maximum only when <br />the following conditions have been met: <br /> <br />1. A location hydraulic study has been performed in accordance with <br />Federal-Aid Highway Program Manual (FHPM) 6- 7-3-2 "Location and <br />Hydraulic Design of Encroachments on Floodplains" (23 CFR 650, Subpart A) <br />and FHWA finds the encroachment is the only practicable alternative (Federal <br />Highway Administration 1979). <br /> <br />2. The constructing agency has made appropriate arrangements with <br />affected property owners and the community to obtain flooding easements or <br />otherwise compensate them for future flood losses due to the effects of the <br />structure. <br /> <br />3. The constructing agency has made appropriate arrangements to assure <br />that the National Flood Insurance Program and Flood Insurance Fund do not <br />incur any liability for additional future flood losses to existing structures which <br />are insured under the Program and grandfathered in under the risk status <br />existing prior to the construction of the structure. <br /> <br />4. Prior to initiating construction, the constructing agency provides FEMA <br />with revised flood profiles, floodway and floodplain mapping, and back- <br />ground technical data necessary for FEMA to issue revised Flood Insurance <br />Rate Maps and Flood Boundary and Floodway Maps for the affected area upon <br />completion of the structure. <br /> <br />(permit applicant) and submitted to the appropriate local officials <br />determining the effect of the proposed activity on future flood heig <br /> <br />1. Valley Cross Sections. The valley cross section of the ch, <br />overbank area must be taken perpendicular to the flow of the st <br />Figure 7). The cross section must extend to an elevation above the <br />1 DO-year floodplain. <br /> <br />Note: Sections right angle to flow <br />omit - not effective to convey flow <br /> <br /> <br />5kew <br /> <br />Floodplain <br /> <br />regular intervals <br /> <br />6. Floodway Impact Analysis <br /> <br />6-1. General. The developer must assemble and provide to the local <br />officials information and analysis results of the effects ofthe proposed develop- <br />ment on future flood elevations. These data will be used to determine whether <br />or not the request for floodway development is approved. <br /> <br />6-2. Data Required. The following data must be provided by the developer <br /> <br />Figure 7: Location of Valley Cross Sections <br /> <br />The collection of field data for use in the calculation of wat <br />profiles requires many engineering judgments and field consideratio <br />performing the surveys it is important to note that the cross sectic <br />be typical of the reach between adjacent upstream and downstr <br />sections. (If available, the original cross-sections used in the F <br />obtained from the appropriate FEMA Regiona Office.) Local irregl <br />the ground surface that are not typical of the reach should be avoi <br />surveys. The reach length (distance between cross sections) must be <br />in the channel and the right and left overbanks. <br /> <br />Control structures such as bridges, road grades, culverts, levees, <br />wing dams in the vicinity of the proposed development must be c <br />appropriate cross sections and reflected in the water surface profil <br />Measurements and descriptions of the control structures should b <br />the field survey books. <br /> <br />Starting water surface elevations must be taken from the b, <br />downstream of the proposed development at the nearest cross sect <br />development is near the downstream end of the Flood Insurance ~ <br /> <br />14 <br />