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<br />r <br /> <br />e <br /> <br />e <br /> <br />e <br /> <br />ATTACHMENT 2 <br /> <br />FPR 98-467 <br />Floodplain Information Report, North St. Vrain & St. Vrain Creeks, <br />Floodplain Update, Town of Lyons, Boulder County, Colorado, June 1998 <br /> <br />KEY ISSUES: <br />. The FIR contains detailed information for North St. Vrain Creek and St. Vrain Creek within the <br />Lyons corporate limits; it does not contain any information for South St. Vrain Creek. <br /> <br />. A separate FIR, prepared for Boulder County in 1987 and designated by the CWCB (FPR 294), <br />contains detailed information for North St. Vrain Creek and St. Vrain Creek within and outside <br />of the Town of Lyons. FPR 294 only designated reaches in unincoroorated Boulder County. <br /> <br />. The new FIR utilized the same hydrologic information as FPR 294, but it incorporated <br />revisions to the hydraulic analysis, including changed modeling of already-existing bridges and <br />ineffective flow areas and new cross sections at the wastewater treatment plant and the new <br />pedestrian bridge. The new analysis found the 100-year flood elevations upstream of the newly <br />constructed pedestrian bridge were approximately 3 feet higher than previous elevations. <br /> <br />. At its upstream and downstream limits the new FIR is consistent with FPR 294. <br /> <br />. The new FIR is inconsistent with the 1980 Flood Insurance Study for Lyons (FIS), designated <br />by FPR 20 I; the new FIR is more current and more detailed than the FPR 201. <br /> <br />. The Town of Lyons is anticipating new development in the study reaches, including the <br />construction of a new bridge across St. Vrain Creek. Designation and approval of the 1998 <br />Lyons FIR will assure that the town is legally provided with the most current and accurate <br />floodplain information available and that appropriate baseline information is in place for <br />analysis and regulation of the hydraulic irnpacts of proposed development activities, including <br />the proposed new bridge. <br /> <br />COMMUNITY RESPONSE: <br />The Town of Lyons initiated the floodplain study and the designation of it by the CWCR. <br />The Town sent a letter requesting CWCB designation of the 1998 FIR. CWCB staff met via <br />several telephone conversations until the completion of the report. The Town is very <br />supportive ofthe Board's proposed designation and approval of the 1998 FIR and rescission <br />of the 1980 FIS. <br /> <br />SUMMARY: <br />The staff recommends Board designation of the floodplain resolution for the Town of Lyons, <br />including rescission of FPR 201. The floodplain information contained in the FIR rneets the <br />Board's "Floodplain Designation and Approval Rules". The designation will assure that the most <br />recent floodplain information for the Town of Lyons complies with state statutory requirements. <br />