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. . . Channel diversion upstream of the Larimer and Weld Canal to diver! Dry Creek to the Cache La Poudre River, . Culvert improvements under several Toad crossings, . Diversion of fIc>Od flows to Terry Lake. The first two plans discussed above resulted in a BfC ratio of less than 1.0. The plan for the cbannel diversi<;m (alignment A) resulted in a BfC ratio of 1.6, however due to environmental impacts and potential hazardous or toxic waste contamination near this alignment, this alignment would not be supported by the sponsor. The plan for the channel diversion (alignment B) resulted in a B/C ratio of 1.I,was supported by the sponsor, and was the selected plan during the initial reconnaissance study. The COIpS of Engineers was requested to conduct a reconnaissance study to revjewthe 1980drainageway plan todctermine the extent of Federal interest in cost- sharing construction of flood control measures. The reconnaissance study was initiated in April 1990. During the review of the previous Gingery Study, several concerns were raised by the Corps of Ertgineers concerning the hydrologic assumptions and the modeling process. The Corps of Engineers then completed a very limited review of the previous sponsor provided hydrologic analysis todetennine new discharges for Dry Creek. These discharges were then used to evaluate four alternative plans and were presented in the draft reconnaissance report suhmitted May 1991. The four alternative plans are summarized below: . Channel improvements (for the IO-year event) in reaches A, B, and C; and also a channel diversion (alignment B) upstream of the Larimer and Weld Canal in reach B to divert Dry Creek to the Cache La Poudre River, . Channel improvements (for the lClO-year event) in reaches A, B, and C; and also a channel diversion (alignment B) upstream of the Larimcr and Weld Canal in The plan selected during lheinitial reconnaissance study met the basic planning objectives: (1) it would reduce, but not eliminate, the flood hazard along Dry Creek below Larimer and Weld Canal; (2) it would be economically feasible, based on reconnaissance-level information: (3) it would minimize the environmental impacts: and (4) there would be a Federal interest in proceeding further. The no--action scenario h the baseline condition to which all alternative plans are compared to. For this reconnaissance.phase study, it was assumed that neither the City nor the County would construct any channel improvements in the near future. Thc cost and benefits associated with the baselinc condition (no action) were assumed to be zero because no Federal construction funds would be required and there would be no reduction in existing flood damages. .....d, E tv Jive,. D.y Cr.:cl.: tv the Co.che La Poudrc River, . Channel diversion (alignmeflt A> upstream of the Larimer and Weld Canal in reach B to divert Dry Creek to the Cache La Poudrc River, . Channel diversion (alignment B) upstream of the Larimer and Weid Canai in reach B to divert Dry Creek to the Cache La Poudre River. A Reconnaissance Review Conference was held on June 20, 1991 and it was concluded that additional studies were needed tocornplete the reconnaissance phase. The additional reconnaissance study effort would include a oew hydrologic analysis, areevaluation of the hydraulics and the economic benefits, and would concentrate additional effort toward reducing damages in the Fort CoUios Airpark area. The loc.atior. ;;;f,;:hilJi;;;:J ..:..,__,__ ~,,_~_~~._ A ~~.. 'D _&~__.. o_;~ .1._ ._~. ..... <0,"''' .....b....'....'.. .. ...,,,... ,,,',,'''''' ~~. "',, -~. are shown on plate 4. . '-7 '-8 .