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Existing 100 -year water surface elevations downstream of Highway 50 range from 0.4 to 5.7 feet <br />higher than the corrected effective water surface elevations. The increase in 100 -year water surface <br />elevations can be attributed to the elevation of Berms B, C, D, and E, which limit the conveyance <br />capacity of the right overbank. Adverse impacts to the floodplain in the existing condition are also a <br />result of Berm F (in the southeast corner of the site) which impedes flow from spreading south as was <br />the case in the corrected effective condition. <br />A comparison of 1977 and 2005 aerial photography is provided in Figure 3.3. Figure 3.4 shows a <br />graphical profile of the existing channel, the overbank ground based upon 1980 and 2008/2009 <br />topography, and the corrected effective and existing condition 100 -year water surface elevations. <br />Comparison of the aerial photography and available topography shows that the configuration of Berm A <br />and Berm A -B has been changed since 1980. The graphical profile of the overbank shows that the <br />elevation of Berm A is approximately 12 feet higher than the 1980 ground. Similarly, comparisons of <br />Berms B, C, D, and E indicate increases in berm heights ranging from 2 to 9 feet. A graphical profile <br />comparison of Berm F from the 1980 and 2008/2009 topography along with corrected effective and <br />existing condition water surface elevations is provided in Figure 3.5. The existing Berm F profile shows a <br />berm height increase ranging from 6 to 12 feet when compared to the 1980 topography. <br />Mapping of the floodplain was not included in the scope of work for the current study. It should <br />be noted that the Valco property boundary is approximately 1,300 -feet in width (from north to south) <br />and located in the middle of the approximately 5,000 -foot wide 100 -year floodplain. <br />COVALCOO1_Phase 11 Report_082211.docx <br />3.6 ANdERSON CONSUITINq ENGINEERS, INC. <br />