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<br />. Channel diversion upstream of the Larimer and Weld Canal to divert Dr)" Creek <br />to the Cache La poudre River, <br /> <br />. Channel diversion (alignment B) upstream from the Larimer and Weld Canal <br />in reach B to divert Dry Creck to the Cache La Poudre River. <br /> <br />. Cu);'en improvements under several road crossings, and <br /> <br />The location of channel diversion alignments A and 13 referred to in the te~t are <br />shown on plate 4. <br /> <br />. Diversion of flood flows to Terry Lake. <br /> <br />The Corps of Engineers was requested to conduct a reconnaissance stud)" to review <br />the [980 drainagcway plan to determine the extent of Federal interest in cost-sharing <br />construction of flood control measures. The reconnaissance study was initiated in April <br />1990. During the review of the previous Gingery study, several concerns were raised <br />by the Corps of Engineers concerning the hydrologic assumptions and the modeling pro- <br />cess, The Corps of Engineers then completed a vcry limitcd review of the previous <br />sponsor-provided hydrologic analysis to determine new discharges for Dry Creck. These <br />discharges were then used to evaluate four altemative plans and were presented in the <br />draft reconnaissance report submitted r>.lay 1991. The four alternative plans are Sllm- <br />maril('dbclow: <br /> <br />I <br />I <br />I <br />, <br /> <br />The ftrst two plans discussed above resulted in a benefit/cost (B/C) ratio of less <br />than 1.0. The plan for the channel diversion (alignment A) resulted in a BIC ratio of <br />1.6; however, because of environmental impacts and )Xltential hazardous or toxic waste <br />contamination near this alignment, this alignment would notbe supported by the sponsor. <br />The plan for the channel diversion (alignment B) resulted in a B/C ratio of 1,1, was <br />supported by the sponsor, and was the sele<;ted plan during the inilial reconnaissance <br />study. <br /> <br />The plan sele<;ted during the initial reconnaissance study mel the ba~ic planning <br />objectives: (1) it would redLlee, but not eliminate, the flood huard along Dry Creek <br />below Larimer and Weld Canal; C) it would be economically feasible, based on <br /> <br />rcconnaissance-Ievel information; (3) it wouiilln1nill\il.c thc ell~irilllmcntal imp..cts; and <br /> <br />. Channel improvements (for the 10-year event) in reaches A, fI, and C and a <br />channel diversion (alignment B) upstream from the Lanma and Weld Canal in reach fI <br />to divert Dry Creek to the Cache La Poudre River, <br /> <br />(4) there would bea Federal intercst in proceeding further. <br /> <br />. Channel diversion (alignment A) upstream from the Larimer and Weld Canal <br />in reach B lodivcrt Dry Crct'k to the Cache La Poudre River, and <br /> <br />The no-action scenario is the baseline eondilion to which all altem<ltivc plan:; are <br />. compared, For this reeonnaissance.phase sttJdy, it was asst\med that neither the City nor <br />thecounly would conslructany channel improvements in the near future. The cost and <br />bt'nefit~ as,oeiatcd with the baseline condition (no action) were assumed to be 1cro <br />b<:eau~no f'ederalconstruetion fundswou[d be required and there would be no red\lc- <br />lion in exisling r.oodllamages. <br /> <br />. Channel improvements (for the lOO-ycar event) in renches A, fI, and C and a <br />channel di,.crsion (alignment Il) upstream from the;: Lanmer and Welll Canal in r"deli B <br />todwert Dry Creek to the Cache La ['oudre River, <br /> <br />57 <br /> <br />,.8 <br />