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In 1989, a ~evhed FrS was publhhed fo~ Arapahoe County (Refe~ence 1). The mapping for Cottonwood Cre..k va. ..xtend..d a~ a limit..d d..tail atudy f~om th.. deuil..d study liolit"d up to the County boundary. the plan and profiles of thh upper ."ctior. fo~ the 100_y"ar flood were traced di~ectly from the FliAD. rhO' flows, however, (according to the FIS ten) are based on a new H"dy by Sato and Associates. 198~ (R..fe~ence 1)._ thO's.. flolls are also lo,",..r than the FElAD flows. We a..u.med that nev hydr&ulica ven! not run fo~ the 1989 FIS because the new flow. a~e only about 10% lower than the FRAD. Since theFIS proHles are based on the FHAD Study, our study aloo u.... the FHAD flows in o~der to maintain sam.. consistency in the profil". and wat..r surface elevations. For the 10*yea~, 50-yea~, and 500_year floods, "'0' used the flo"" directly from Fig"r.. 5 of the FIS. We have append..d copi"s of the plans and profiles from the fIS and FHAD. Bela", is a'WI1lIIarytable listing th" various discharga. in the vicinity of the project site. Station 283+55 and the .ame location at County Line Road. rhu., our Station 295+45 is the Same a. FIS Station 295+30. The .tudy l~it for the CLOMR for Little People'. landing i. hetveen Station. 288+Z5 and 290+81, on the ",e.t .ide only. The "alculations, hOwever, extend throug~ the .ame otationing as used for the LoKR. IV. NAPPING The HEC_2 is based on Held 'u~eyed cro.s-section.. In hetween crou_ section. we use topog~aphic mapping from an aerial photog~aphy at a scale of 1" - 200', enh~ged to I" - 100' (Reference 4). Contour inte~als vary between 1 foot snd 2 foot. v. HYDRAULICS Sometime bet"'een 1975, ...hen the FHAD "'as done. and Janua~y 1990, Cottonwood Creek ",a. realigned (straightened) for a!>out 1,200 f....t belo", th.. County line. The new topog~lIphy is sho,",n on the enclosed phns and restudied herain. TABUl 100~YE~R FLOOD FLOV COHPARISON All hydraulic "aloul..tions vefe done using th.. U.S. Army Corp. of Enginee~s HEC_2 step_backwater program (ReferenCe 5). Hanning 'n" values range bet...eenO.035 to 0.45 for the channel and 0.030 to 0.040 for the bank s. The On" value. for the bsnks an lower then the channel due to the bank, being lined with moved hlue grass or native I';ra.... The ohAnnel tend. to be thicke~ wet lend type vegetation from intermittent .t~ea'" flows. Statio" ,.S Q. cfa FliAD Q. ds Starting wat..r .urface elevation at Station 283+55 was taken from the FRAD/FIS p~ofile at 5772.9 feet !lGVD. The final water .urhce eleVAtion at Station Z95+45 (FIS Station 295+30) was calcuhted in the f1EC*2 at 5785.5. the FIS profile .how. this .ection to be al.o At approximately 5785.S. Z83+5S" 4600 5000 287+55 4370 4500 .. FHAD Station 175.55 III. S~JDY ~L~IT There are four HEC-2 run. appended to this report. The study starts At FtS Station 283+55, ",hich is the s.me as the FRAD Station 175.55. The study extend. for app~o:d"'ately 1,200 feet to the base of the down.tresm side of the culvert crossing at County Line Road (Inve,ness Drive). The FrS Study has" alightly .honed length of 1,175 feet between L ,. 100_yea~ floodpl.in .nd flood".y using existing (19QO) topography. 10_yur, 50_year, and 500-year floodplain u.in8 edating (1990) topog~aphy. p.opoaed develop~ent fo~ Little People'. Landing. C.lib~lItion ~un. " ,. , ,