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I I A discharge profile througMut thestlJdy reach for each flood event is shown in Figures3and4forexistingandfullydevelopedconditions. respectively. Some typica\hydrographsforthel00-yeareventarepresentedinFigures5and6. Tile lQwerdischarge:; calculated in our stu<!y can be attributed to th e four natural detention areas previously mentioned. These areas were considered in the present study and not in the Flood Insurance Study. These detention ~~as contribute to the redudion of peak discharges east of Taft Hill Road. The lOO-yearundetained flow for existing basin conditions w~s also examined and found to be within lO~ The importation of flood flows byrneans of the canals had little effect on the total discharges for this study. Inflows from the l;anals generally did not l;om- binewiththemain peak flows that were generated on Spring Creek. Therefore, the maximum increase in peak discharge for the lOO-year flood event due to canal importation is estimated as 300 to 400-cfs anywhere along Spring Creek. of the discharges in the FIA study. Amore thorough description of the hydrology prepared for this relXlrt is presented in the Technical Addendum. KYORAULlCS Procedure Discharges were also developed for the lOO-year fully developed basin without considering inadvertent detention storage at roadway and railroad embankments. (Undetalned flow) These values are shown in Table 7. A hydraulic analysis was completed along the 7.5 mile study reach to determine water surface profiles for the 2~year, lO-year, 25-yedr, 50-year, laO-year and 500- year flood events for existing and fully developed conditions. These water surface elevations were computed using the HEC-T! conputer model for backwater analysis (Reference 21). Water surface profiles for these flood frequency events are present- edonSheets16ttrrough29. ThelO-year,50-year,100-yearand500-yearfrequency Discharges forexistingdevelopmentdeterminedlnthisstudyasl;omparedtothose developed in UlC FlOOd InSUrdflO! Study (Frs) for Spring Creek are listed in Table 7. "dtt'r ,~rrdLe el~v~tion~ dt ~~ch of the cross s~ctions are t;;bulated in ":";;ble ~. Table 7 Cross sections used in this study were developed from field surveyed information. These cross sections were supplemented as required with cross sections taken direct- lyfromtopographicmapping. The geometry of all crossing structures was freilsured iuthefield. FIA Oischnlles: Existinlj Development Without Canal Importatio.~ Locdtion 100-Year FIA Study lOO~Year This Study lOO-Year Undetained 1 ,570-cf~ 1.000~d, 3,lOO-cr, 1,870-cfs 1,6S0-cfs 4,500-cfs 2,65O-(f<; 1,740_cfs 4,800-cfs 3,300-cf5 2,150-ds 5,OOO-cfs Manning'sroughoesscoefficientS("n"va1ues) "eredeterminedth rough fleld in- Shields,il,venue College Avenue L"MayAvenue Confluence with Cache La Poudre River spection. AphotOgraphicsunmary, by reaches, of the Spring Creek floodplain was prepared,andthe"n"valuesusedforchannelandoverbankareaswere presented to the Technical Comittee for review prior to completion of the hydraulic _17_ -18-