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<br /> <br />e <br /> <br />e <br /> <br />e <br /> <br />Redstone <br /> <br /> <br />upward bound of possible "n" values based on observed existing <br />conditions. The resulting water-surface prof~~e revealed a <br />negligible increase. The HEC-2 file is included in Appendix B as <br />"NEWRSN61.0UT". <br /> <br />The model was run containing the 100-year and 500-year flow <br />events to the main channel and left overbank area. This was done <br />to estimate the required height to contain these floodflows with <br />either raising the existing levee or constructing a new levee <br />along the right bank within the study reach. The results shown <br />on the summary table below, as well as the fourth water-surface <br />profile in Appendix A, indicate only a slight rise (0 to 0.7 <br />feet) under the encroached conditions throughout the study reach. <br />This is because (1) flows were contained within the levee system <br />under existing conditions between cross sections 87-DF and 91-DF <br />even though FEMA criteria is violated and (2) the right overbank <br />area is relatively non-effective for additional flow capacity in <br />the existing non-leveed reaches. The data indicate that flanking <br />a new levee at the upstream end would not be a problem as long as <br />any levee improvements are tied to high ground. Also, the water <br />surface rise upstream and downstream as the result of levee <br />improvements would be very minimal. The HEC-2 file is included <br />as "NEWRSENC.OUT" in Appendix B. Cross sections under encroached <br />conditions were plotted and are included in the second half of <br />Appendix C. <br /> <br />The table below lists the following information for each <br />cross section (starting at the downstream end): cross section <br />number and corresponding FEMA designation; the 100- and 500-year <br />peak flows (in cubic feet per second, as identified in the flood <br />insurance study); the average channel velocity (in feet per <br />second) under encroached conditions; the existing and encroached <br />water-surface elevations at each cross section; the existing <br />right bank (or existing levee crown) elevation; existing <br />freeboard on the bank or levee above the 100- and 500-year <br />events; and, finally, how much higher a flood control structure <br />(presumably a levee) would have to be than the existing bank or <br />levee to have 3 feet of freeboard above the 100- and 500-year <br />water-surface elevations. (NOTE: This last column should not be <br />misinterpreted; based on available data, the levee in its present <br />state would likely not be a viable flood control structure by <br />simply adding a few feet of embankment material on top of the <br />levee. ) <br /> <br />5 <br />