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<br />Guide For Approximate Zone A Areas <br /> <br />Developing BFEs <br /> <br /> <br />Figure 9 - Contour Interpolation Method - <br />Riverine Flooding Example 2 <br /> <br />Determining BFEs for Lacustrine (Lake) flooding: <br /> <br />Determine the contour elevations that the approximate Zone A <br />boundary crosses (i.e. the BFE) around the perimeter of the <br />lake or ponding area. Assuming that the highest and lowest <br />determined water-surface elevations are within one-half of the <br />map contour interval of each other, add one-half of the map <br />contour interval to the lowest water-surface elevation to <br />determine the BFE for the site. <br /> <br />Example 3 <br /> <br />Using aU. S. Geological Survey quadrangle map with a <br />contour interval of 10 feet, the approximate Zone A <br />boundary crosses low and high determined water-surface <br />elevations along the perimeter of the ponding area of 280 <br />and 283 feet, respectively, as shown in Figure 10, <br />"Contour Interpolation Method Lacustrine Flooding <br />Example 3." The difference between these two water- <br />surface elevations is 3 feet, which is less than one-half <br />of the contour interval or 5 feet. Therefore, this <br />method is acceptable for use on this ponding area. Add <br />280 feet (lowest water-surface elevation) and 5 feet <br />(one-half of the contour interval), which yields a BFE of <br />285 feet. <br /> <br />V-5 <br />