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<br />. <br /> <br />. <br /> <br />, <br />I <br /> <br />. <br /> <br />the results. The widths of the flooded area, which can be estimated <br />from the plot of each cross section, are then transferred to a map <br />of the area. By connecting the end points of the flooded area at <br />each cross section on the map, the approximate outline of the 100- <br />year flood can be shown. In lieu of detailed topographic maps, <br />aerial photographs are the next best aid in determining the flooded <br />area outline. For this study, three sets of aerial photos were used <br />for this purpose and were flown on the following dates: <br /> <br />September 23, 1955 <br />July 28, 1963 <br />July 5, 1973 <br /> <br />Careful study of these photos revealed considerable variation of the <br />main channel in the floodplain. <br /> <br />A summary of the hydraulic calculations for Anthracite <br />Creek near Erickson Springs is shown in the following table. One- <br />4u~dred year flood depths are expected to range from 3.4 feet to <br />~feet above streambed elevation. Flooded widths are expected to <br />range from 150 feet to 600 feet at the cro~ss sections. Average <br />. . 3~"'-- '7, <br />veloclty lS expected to range from.~~ to feet per second for <br />the 100-year frequency flood. <br /> <br />)'6 <br />J:fJ~ <br />