<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
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