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e e e Redstone EXISTING BANK/LEVEE CONDITIONS AND LIKELY REQUIRED IMPROVEMENTS As indicated in the summary table, the existing bank adjacent to the sewage lagoon and fire station (between cross sections 82 and 83) is slightly below the 100-year flood elevation. However, the sewage lagoon berm itself appears to be slightly higher than the adjacent natural bank and Pitkin County indicated that it is not concerned about the flood threat to the lagoon (which was not flooded in 1985). Therefore, no potential project quantities or costs were developed for this site. Nonetheless, it would be advisable to include this area in any future detailed analyses to verify that it is not vulnerable to flooding. The existing levee extends from just upstream of cross- section 87 to the Coal Creek confluence between cross sections 90 and 91 (Attachment 3). The upstream 1,550 feet of the levee was originally built at the turn of the century and has been periodically enlarged since. Following the 1985 flood, the Soil Conservation Service (SCS) constructed a 250-foot emergency levee downstream of the existing levee and Pitkin County built an additional 400-foot levee beyond that. These two levees were apparently constructed to a large extent from the adjacent riverbed materials. The levee lacks adequate freeboard for both the 100- and 500-year events. Immediately downstream of the levee (cross-section 87) where the 100- and 500-year flood elevations would exceed the bank elevation by 1.7 and 2.7 feet. Therefore, it would be important to have any future levee improvements tie in to high ground, especially at the downstream end, to prevent backwater flooding (and at the upstream end to prevent flanking). FEMA standards (Appendix D) require a mlnlmum 3 feet of freeboard (as well as various other criteria). The existing levee has a freeboard range of -1.7 to +2.4 feet for the 100-year event and -2.7 feet to 1 foot for a 500-year event. Therefore, a significant increase in levee height would be required to meet FEMA standards. The 29 supplemental cross sections of the levee which were surveyed by Pitkin County (under contract) for this study verify that the levee not only lacks sufficient height but also lacks structural integrity through much of its length. These cross sections along with a profile of the crown elevations were plotted and are compiled in Appendix E. Further, previous studies make reference to the levee being composed of unconsolidated material and could be eroded by the sustained high flows of a snowmelt flood. The recent Corps Non-Federal Levee Inspection Report (Appendix F) substantiates this. As part of the inspection, a limited geotechnical analysis was made. The 7