FLOOD05212 - Laserfiche WebLink

Home Browse Search

. The sdJeduled reconnaissance study extension resumed during May 1992. At the beginning of the study e.l:ten.sion the follov.ing four alternatives were f ormulated; . Channel diversion (alignment B) upstream of Lariiner and Weld Canal in reach B to divert Dry Creek to the Cache La Poudre River. . Channel diversion to be located west of the Airpark area heginning at East protcct the Airpark area. Itsbouldbenotedthatduringthefeasibilitystudy eon~iderably greater detail is involved in the flood damage analysis, including obtainiog more accurate and detailed building content values'which may significantly change the damages in the Airpark area. . VilleSlreet. . Channd diversion to he located east of the Airpark area beginning at East Vine Street. TILis location was identified by the City of Fort Collins and Larimer County as being the preferred Airpark location. . Channel diversion (alignment B) and also a channel diversion or channel improvements in the Airpark area. The channel diversion (alignment B) upstream of Larimer and Weld Canal in reach B to divert Dry Creek 10 the Cache La Poudre RiveT was selected as the plan !o evaluate during the study exten:;;ion. Thisplanwasevaluatedforty,'owith'project conditions using peak flows from the new hydrologic analysis. The two conditions evaluated were diversion channels to convey the peak loo-year and 30-year discharges. The design discharge (upstream from the Larimer and Wcld Canal) for the lOO-year diversion increased from 2,830 d.s. to 5,022 d.s. The design discharge for the 30.year diversion is 2,830 c.f.s., which equates to the previous 100- year design discharge. The last three alternatives were originally formulated to address the high damages in the Airpark area. The previous reconnaissance study had shown that exiting cstimated a."illual damages in the Airpark area were 50 percent of the total damages and that residual damages were also high. However, after the hydrology v,a<;reevaluated these three alternatives were eliminated from further consideration , because the damages in the Airpark area under existing conditions were significantly reduced, and the original channel diversion (alignment B) would prevent most of the flood damages to the Airpark. H the original diversion were implemented, residual flows in the Airpark would he so small that the residual flooding problem could easily be corrected by local interests. Rased on the preceding information, an additional diversion to protect the Airpark area would not be needed. The reduction of existing estimated annual damages for the Airpark area is primarily a result of the lower discharges and associated lower damages for the 2-, 5-, and 100year events. The discharges for the 50, tOO, 500-year events havc increased, as have tbe damages associated with these events, however, Ihe estimated nnnual damages (EAD) estimated althis time werc not sufficient lojustifycurJl;truction ofa diversion 10 Both the lOO-year and the 30-yearchannel diversion plans were analyzed. The benefit/cost ratios (B/C) were 0.86 and 1.2, respectively_ The tOO-year channel diversion plan is not econorrllcally feasible. The 3{).year channel diversion is feasible. The analysis of both of the studied plans is presented in Chapter 6, Evaluation of With-Project Condition Plans. . 5-9 5-10 .