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Description of Dry Creek Floodplain Dry Creek is a left bank tributary of the Cache La Poudre River. Dry Creek flows south through the northeast portion of Fort Collins before joining the Cache La Poudre River south of Fort Collins Airpark (Figure 1). The basin is about 23 miles long and 3 to 3.5 miles wide and has a drainage area of about 65 square miles. Basin elevations range from 6960 feet, m.s.l. near its headwaters to 4910 feet, m.s.l. near its mouth. The Dry Creek floodway has a width from 600 to 1,200 feet within the urbanized area of the City. In the upper portion of the basin, the stream is steep, narrow, and deeply incised with active headcutting. Lower in the basin, the Dry Creek channel is relatively stable with wide, shallow floodplains except downstream of the Larimer and Weld Canal, where the channel does not exist in several areas. Upstream from the Alta Vista Community, the Dry Creek channel is undefined except for a small drainage ditch just downstream from College Avenue. Extensive commercial and residential development is located within the Dry Creek floodplain from College Avenue to the Larimer and Weld Canal within the City limits. Downstream from the Larimer and Weld Canal, the Dry Creek channel has been obliterated from Willox Lane to downstream from the trailer court at College Avenue. In the Fort Collins Downtown Airpark, the disposal of building material and other fill in the Dry Creek channel has reduced the flow conveyance of Dry Creek. The filling and regrading activities within the Dry Creek channel took place prior to the City and County entering the National Flood Insurance Program and prior to the enactment of floodplain management regulations which now prohibit such activities. Presently, the impact of new development in the lower basin of Dry Creek is already increasing the magnitude and frequency of drainage flows. In the past, much of the excess drainage from irrigated farmland was intercepted by irrigation canals. Today, these canals no longer have the capacity to intercept larger flood flows and increased drainage flows. The irrigation canals should be bypassed with proper conveyance provided in the drainageway. Figure 2, Dry Creek Existing Floodplain, shows the delineation of the floodplain and floodway from just north of Will ox to Mulberry Street (Highway 14). The delineation includes areas located within the jurisdiction of Larimer County and the City of Fort Collins, and depicts the most developed portions of the floodplain. Photographs 1 and 2 show aerial views of the North College Avenue corridor portion of Dry Creek. The approximate floodplain is delineated by red and the approximate channel by black dashed lines on both photos. Photograph 1 is looking northeast from downtown and photograph 2 is looking south from Terry Lake. The channel, delineated by dashed black lines, has been obliterated throughout most of the reach by pre-Firm development and grading. The remaining portion of the "native" channel, visible as a line of trees, has been identified as a natural resource area and is observed in the upper left (northwest) portion of photo 1. The Cache La Poudre River is visible in the foreground of photo 1 and the background of photo 2. 3