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<br />. <br /> <br /> <br />. <br /> <br /> <br /> <br />it; <br />. <br />. <br />.'fE. <br />. <br />. <br />. <br />. <br />II ,,'. <br />. <br />. <br />t. <br /><< <br /> <br />. <br /> <br /> <br />Methods for developing <br />BFEs <br /> <br />. Simplified methods <br />, !j. X feet above NGVD (sea <br />level) <br />." <br />. X feet above crown of <br />road <br />. X feci above highest <br />adjacent grade <br />. Culvert (HWfD) (FHA <br />Charts) <br />. Contour interpolation <br />. Data extrapolation <br /> <br />Detailed methods <br />. Normal depth hand <br />calculations <br />. QUlCK-2 <br />. Computer models <br />. HEC.2, WSPRO, <br />WSP2,etc. <br /> <br />Contour Interpolation <br /> <br />Obtain a topographic map of the site <br />Reduce or enlarge the topographic map to the <br />scale of the FIRM <br />Superimpose the Zone A floodplain boundary <br />onto the topographic map <br />Determine If the noodplain boundary conforms <br />with the contour lines within acceptable <br />accuracy Iimits-- (elevations of the left and right <br />overbanks must be within one-half of the <br />contour interval of the map <br />If the method is reasonably accurate, determine <br />the BFE <br /> <br />Data Extrapolation <br /> <br />~ 1\pplicability <br />! . Site must be within <br />500 feet of the detailed <br />study area <br />. Site must have <br />floodplain <br />charRcterisitlcs <br />similar to the detailed <br />study area <br />. Site must have no <br />hydraulic structures <br /> <br />. Steps <br />. Determine the location of <br />the site on the flood <br />profile for the detailed <br />study area <br />. Extrapolate the last <br />segment of the nood <br />profile that has a <br />constant slope to the <br />location of the site <br />. Determine the BFE from <br />the extrapolated profile <br /> <br /> <br />verlay FIRM With Topo Map <br />(Contour Interpolation) <br /> <br /> <br />a Extrapolation: Extend Profile <br /> <br />. <br />. <br />. <br />. <br />. <br />" <br />.:\ <br />.if <br />:& <br />. <br /> <br />- <br /> <br /> <br />Culvert (FHA Charts) <br /> <br />. Diameter of Cui vert <br />(D) in Inches <br /> <br />. Discharge (Q) cfs <br /> <br />. Headwater Depth in <br />Diameters (HW/D) <br /> <br />. Solve for Headwater <br />Depth (HW) <br /> <br />" ,. <br /> <br />~ "'-;:-; .' <br /> <br />I: .L/',:-~: <br />I ~ I'" <br />! ~''1 L._ __ ':- <br />1 ~ :::<f I, : : <br />!~ <br /> <br />I: <br /> <br />-"-- <br />-. -_:--~= ";.':':"..;;'-~... <br /> <br />5 <br />