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<br />FREQUENCY <br /> <br />~t ~ vc.lociry of _~ or- nor-c f'let ~er- second could Ildsi Iy Swf'e~ i1n <br /><'Id"1 t n.erson 0+/ hi s feet, thu~ crcatin1 def inite danQ(Jr 0/ <br />n.iuryordrownino. RapiJlyrlsinQandswl/tlyflcwinqflood- <br />'Irlter-maytraopl'rsonsinllOmesth<'ltare"ltimatelydostroyed <br />or i r, vch ie leJ that arc ultimately submerqed or f loate'), Isola~ <br />tion of areaS ty floodwaters could create ~zards in terms of <br />medical, tir-o, or lawenforc,,",cntorncrqenclos. <br /> <br />The50Q-yoarflood is not the largest flood that Can <br />occur but the proba~il/ty ot larger floods is remote, AS can be <br />scen from the gaging records for Cherry Creek, discharQes smaller <br />than either the IOO-ye~r or 50C-year floods are much more common, <br />Large floods, however, can happen; this waS clearly demonstrated <br />by the Denver area floods ot 1965, the June 1972 tlood at Raoid <br />City, Sovth Dakota, and the July 1976 flood In the Big Thompson <br />Canyon near Loveland, Color~do. <br /> <br />Flooding Can occur with rel~tively little discharq~ in <br />theevontotchannel blockage caused by debris or ice. Inthp.se <br />situations, water surf~ce eievations rise until relief is aChieved <br />by flOws over the flood plain, Historical data, however, indi- <br />cate that obstrvctions due to ice are not likely to occur in the <br />stvdy reach. The tormation ot obstructions at bridges in the <br />stvdy reach is, however, quite possible, especially dve to debris <br />accumulation. <br /> <br />FloodOd areas and flood damaqes ~ Water surface <br />orotilcs tor the /ioods studied in this report were d.welooed <br />usin<:)theh.'lckwatl'lr'comlluterpr0'1ramHEC-2,"WaterSurfacePro- <br />liles",deveiopedllytheU. S.ArmyCorpsofEnqlneers, ThecO"'- <br />Dutations w~re based on channel and Ilood Dlain conditions as <br />representQd by survey data cptherQd in A;ril 1975 and as supple- <br />mented by later fielc investigations, <br /> <br />flAZARDS OF LARGE FLOODS <br />The extent 0/ damage caused by any flood depends on the <br />topography of the "ra., f loo<le<:l, d''lP~t> and duration 01 11001 in<1, <br />v..,loc i ty of I low, ra ~e of r i sa, dev" lopments on the f iood pill in, <br />amount of debris in the floodwater, and ice conditions, If ice <br />is a problem in that particolar area. A lOa-year flood or a <br />500-year flOOd on Cherry Creek in the study reach would resolt <br />in the inondatlonof and subsequent damage to primarily '1grlcvl- <br />turlll properties and associated deve I oprnonts as"ell as public <br /><.Iti 1 ities an" publ;c rO!l""ays. n.-..p lloo1..at..r f I"wln'] ,,~ h inh <br />velocity and carryinq floating <lebris would create conditions <br />hazardous to persons and ,ehtclo~ ~ttcmpting to cross llooded <br />areas, In g~neral, floodwater 3 or moro feot deep ~nd flowing <br /> <br />T~e Pro! i Ie on ~Iates 29 t~rouqh 53 shows the water <br />SlJrf~ce elev.,tjon~ ,,~d wdter dept~ of the 10-v"ar. 50-v"i1r, 100- <br />Vc~r, i1~" 500-year fl00ds relative to th.-. stredmhed. In this <br />parti Cll I ar ca~a and thr-O\H1~OlJt thi 5 study, the ~tre5mh<ld is <br />",,,t'MII Y thH ch"rIn" I low Ilow wilt,'r ~lJrl~c"." levation s.ince tn" <br />~urvcy~ were coedlJcte1 by aori,,1 photo~r,,~)tric met~~s. T~ <br />wator $urf",;e "I.f'v"tlo~" of the 100~year i1nd 500-y"dr t loods wer'" <br />u~cd to determine .f lood I im; ts on the cros~ 5"ction5 and tODo~ <br />qra"hic mapS, The rAS" I ts ~r<l shown on tho F/oodnd Areas, p lat(')s <br />;. throuqh 28, An Index to thc Flooded Areas ~IMe5 is on plate <br />2. r,epr050nt"ti V" ero", ,"cti,,<)~ dra i II"strated on plate 54, <br />be cross ~"cri()ns show arOlJn<l elevations across the vallc\' on <br /> <br />bot~, ::ce~ of he c~'~".n~~ ~."~ ~hc 1",~~h:: <J' cV(>"'~3e". "oo~i"'l' <br /> <br />,'leference points, coincidinG with the 10catiOl1sof tM cr05S s"c- <br /> <br />ti,)c,c" ~r'" s~",,,n Qn the rloodeJ ,',redS a~~ Pro!i Ie fo~ corrcl"tio~ <br />~etw"",~ ~he dr"winas. Tahl" 6 ~f"'Ovi:l"s d<lta at rolc~"nc" noi~t <br /> <br />" <br /> <br />" <br />