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A Reconnaiss.ance Revie...... Conference was held on 20 June 1991, and It was con- cluded that additional studies were needcJ to complete the reconnaiss.ancc phase. The adJitional reconnaissance study effort would incluJe a new hydrologic analysis ami reevaluation of the hydraulics and the economic bend!ts, and would concentrate addl- tional effort to......ard reducing damages in the FonCol1ins Airpark area, diversion (alignment B) would prevent mOSt of the flood damages to the Airpark. If the original diversion were implemented, residual flows in the Airpark would be so small that the residual flooding problem could easily becorrccted by loclllinlerests. Based on the preceding information, lIn additional diversion to protect the Airpark area would not be needed. The reduction of e).:isting estimiiled annual damages for the Airpark area is primarily a result of the lower discharges and associated lower damages for the 2-, 5-, and lO-yearevents. The discharges for the 50-,100-, 5oo"yearevcllts haveincrcascd, liS hllve the dllmages associlltcd with these events; however, the EAD estimated at this time was not suffieient to justify eonstruction ofa diversion to protect the Airpark area. It should be noted thlltduring the feasibility st\ldy, e0nsiderahly grca terdetailisinvolvcd in the flood damage analysis, including obtaining more lIeeurate and detailed bllilding content values whidl may significantly change the damages in the Airpark area, The scheduled reconnai,san~e study e).:t~nsion resumed during May 1992. At the beginning of the study extension, the following fouraltcrnatives were formulJted: . Channel diversion (alignment B) upstre<lm from Larimer and Weld Canal in reach B to divert Dry Creek to the Cache La Poudre River. . Channel diversion to be located we~t of the Airpark area hcginning at &st Vine Street. The channel diversion (alignment B) upstream from Larimer <lnJ Weld Canal in reach B to divert Dry Cr~k to the Cache La I'oudre River was selected as the plan to evaluate during tile study extensi0n. This plan was evaluatoed for two with-project conditions using peak flows from the new hydrologic analysis. The two conditions evaluatcd were diversion cnannds to w"'''y thep"..... lOO.y<:<<rand30-ycardischargcs. The design discharge (upstream from the Larimer and Weld Canal) for the lOO-year diversion increaseJ from 2,830 c.f.s. to 5,022 c.f.s. The design discharge for the J().ye<lr diversion is 2.830 c,f.s.. which eqnates to the previous lOa-year ,lesign discharge. . Channel diversion to be locatl'deast of the Airpark area, beginning at East Vine Street. ThiS locati0n was identified by the City of Fon Collins ,\llll Larimer COllnty ax bcingmeprderrcd Airparkloca:ion. . Channel diversion (alignment 13) and aho a channel diver,ion or ~hanllel improvcmentsin the Airpark area. Thc last three altemativex wereoriginaJl)' fornlLilated to addrCiiS the high damages in the Airpark area, Thepn;viousreeonnai.\S<1nee study had shown that exiting estimated annllal damages in the Airpark arca were 50 percent of the total damages and that resid- ual rlamag..s wne alSl) high. However. after the h:,'drology was reevaluated. these three alt~'mati~'es were eliminated from furtt,cr comiderali()n becaulc the damages in the Air- park area under existing. conditions were signiflcantl)' reduced and the original channel Both the lOO-vcar and the 3Q-y..:ar channel diversion plans were analyzed, The B/C ratios were Q,86 and 1.2, respeclively, Thc loo-ycar channel diversion plan is not economically fcasihlc. The 30-ycar charmel diversion is feasible. The analysi, of both of thl' ~tlldi,x1 plan~ is presented in Chapter 6, [vnluation oLWith.l'roicct Condition ~. '.9 5-10