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<br />Guide For Approximate Zone A Areas <br /> <br />Developinq BFEs <br /> <br />Simplified methods may not be used by the community to <br />complete an Elevation certificate .used for flood insurance <br />ratinq. communities must use the detailed methodoloaies <br />described in this section or other methods comgarable to those <br />in a Flood Insurance Studv for comgletina the Elevation <br />certificate. A flood insurance policy for a structure for <br />which a simplified method is used may be rated without an <br />elevation certificate. However, the flood insurance rate may <br />be higher than if the structure is rated using an Elevation <br />Certificate. <br /> <br />contour Intergolation <br /> <br />Contour interpolation involves superimposing approximate Zone <br />A boundaries onto a topographic map in order to estimate a <br />BFE. BFEs obtained by this method can only be assumed to be <br />as accurate as one-half of the contour interval of the <br />topographic map that is used. Therefore, the smaller the <br />contour interval of the topographic map, the higher the <br />accuracy of the BFE determined from the map. The procedures <br />for using this method are outlined below. steps 1 through 5 <br />are the same for both riverine and lacustrine (lake) flooding <br />sources. <br /> <br />step 1 - Obtain a topographic map showing the site being <br />analyzed <br /> <br />step 2 - Reduce or enlarge the FIRM or topographic map as <br />necessary so that the two are at the same scale <br /> <br />step 3 <br /> <br />- Superimpose <br />floodplain <br />topographic <br /> <br />the approximate Zone A <br />boundary from the FIRM <br />map <br /> <br />(lOD-year) <br />onto the <br /> <br />step 4 - Determine if this method is within the acceptable <br />accuracy limits. The floodplain boundary must <br />generally conform with the contour lines along the <br />flooding source in question. The difference <br />between the water-surface elevations determined on <br />the right overbank and the left overbank must be <br />within one-half of the map contour interval. For <br />lacustrine flooding sources, the difference between <br />the highest and lowest determined water-surface <br />elevations around the flooding source must be <br />within one-half of the map contour interval. <br />Otherwise, this method is not acceptable. <br /> <br />step 5 - If the method is acceptable, then determine the <br />BFE. Detailed guidance for determining the BFE is <br />provided below. <br /> <br />V-2 <br />