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'2 overtopping the 8th Street embankment, approximately 1,800 feet downstream of the intersection of 8th Street and Ash Avenue in the unincorporated areas of Weld County. This overflow results in a reduction in the 100-year flood discharge in the reach of the Cache La Poudre River from approximately 3,500 feet downstream of Ash Avenue to approximately 600 feet upstream of 8th Street. This reduced discharge, combined with the effects of the bridge reconstruction at Ash Avenue and 8th Street, results in a decrease of up to 2 feet in the base (tOO-year) flood elevations (BFEs) in the reach from the corporate limits (approximately 1,050 feet downstream of U.S. Highway 85) to 5th Street. As a result of the decrease in the BFEs and the more detailed topographic information, the Special Flood Hazard Area has decreased along this same reach. The zone designation in the low-lying area north of 8th Street has been revised to Zone AO Depth 2 feet. This revised zone designation is consistent with the zone designation for this area shown on Panels 0628 C, 0636 C, and 0637 C of the effective FIRM for the unincorporated areas of Weld County, dated September 28, 1982. The overflow condition described above also has implications for the delineation of a floodway in the area. A floodway is defined as the channel of a river and the adjacent land areas that must be reserved in order to discharge the base flood without increasing the water surface more than a designated height. The allowable increase in this case is 1 foot. The designation of a floodway along the channel of the Cache La Poudre River adjacent to the overflow would allow for the total development of the remaining floodplain provided that structures or properties were properly elevated above the BFE. Theoretically, this development could eventually totally obstruct, and thereby eliminate, the overflow. Our analyses show that returning the entire 100-year flood discharge to the channel would increase the BFEs in this reach by approximately 2 feet. This means that the designation of a floodway in this reach is inappropriate. In fact, any floodplain development in this reach, whether adjacent to the Cache La Poudre River or in the overflow area north of 8th Street, could reduce the overflow and result in an increase in the BFEs. Because the designation of a Hoodway would be inappropriate in this reach, we have removed the floodway designation along the Cache La Poudre River from the corporate limits (approximately 1,050 feet downstream of U.S. Highway 85) to 5th Street. The decision to remove the floodway designation in this reach is based on the best information available at this time. A permanent solution may require coordination between your community, Weld County, and our Regional o.ffice. We are informing our Regional o.ffice of this situation by separate memorandum. The modifications are shown on the enclosed annotated copies of FIRM Panel 0002 B, FBFM Panel 0002 B, Profile Panel OlP, and the Summary of Discharges, Floodway Data, and Flood Insurance Zone Data Tables for the Cache La Poudre River. This Lo.MR hereby revises these panels of the effective FIRM and FBFM dated July 16, 1979, and the Flood Profile, Summary of Discharges Table, Floodway Data Table, and Flood Insurance Zone Data Table in the FIS report dated January 1979.