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<br />C~oss~soction d~t3 and to~o9~anhic ~aPDin~ havinq a
<br />contou~ i nterva I Of 2 I",,,t and a Sea I 0 of I" : !'D~ teot w'lr('
<br />esta~1 iShed ~y ~hotogr~trie "I<:'thods t~"", fl I!]ht, """1,, in
<br />Ap~1 I 1975, These data "erp. turn i shod tly tho Urban [')~<JI nll'lo "nd
<br />Flood Control Dist~ict, ; n cooper"t ion "ith th" ColoradO Water
<br />Conservation Hoard, DouqlilsCounty, and ,A,-apahoe County. U. S.
<br />Goological Su~v"y 7,5 minute quad~angle maps ~Ith 10 and 20 loot
<br />contour inte~va 15 at a scala of I I nch equal s 2,1)00 feet were
<br />also usod In the study. Brldqe and ro~dwilY survey data ~~re pro~
<br />vidad by tha Color~do Wilter Conservation Board.
<br />
<br />FACTORS AFFECT I fiG F LOOO I fiG AND ITS I ~iPACT
<br />
<br />Obstructions to floodflo~s - There are seven road~ays
<br />~hich c,-oss tho Chorry Creek flood plain doscr;bod In this roport,
<br />Ar"p~~ Road and Colo~ado State Hiqh~ay 86 pres"M the lar~est
<br />potential for obstructing floodflo~s.
<br />
<br />FLOOD SEASON AND FLOOD OiARACTERISTICS
<br />Th~ Ch~rry Creek basin is located within an area which
<br />is prone to receiving verv intense rainfall '-Omct;mesotcloud-
<br />burst rnagnltua<l, Floods have ~Asulted from stor"s covering I;,rq(>
<br />areas receiving he,wy gene~ai' rainfai I as ~"II as Irom sto~"'s
<br />coverino 5I'1a II "reas but nroducin<1 oxtremely intons~ ral nfa II.
<br />~ lcods genera Ily occur in thll poriod fro", ~by throuoh August,
<br />Annual peak dl5cha~ges in the study reach. howovor, havo boon
<br />recorded Irom February thl"<)u'Jh S"iltAm~cr.
<br />
<br />~anmade objects, such as buildings, cars, and lences,
<br />as ~ell as trees, brush, and other ve'letatlon located on the f lcod
<br />plain can also cause flo~obstructions. These items, whller~ln-
<br />Ing In place, not only tend to create hIgher stagos on the flood
<br />plain because of reduced flo~ area and flo~ blockage bvt may also
<br />create higher locallled velocitIes as tho flood ~aters flo~ around
<br />them. If the IloodfJo~s are of sufficient ma'lnitude to dislOdge
<br />those flo~ obstructions, flood staqos may lo~er in that localized
<br />area. The debris ""'y then lodge M locations farther do~nstream,
<br />thu$cornpoundingproblems. This floating debrlSCOnrTlO/1ly lodges
<br />against brldgo piers and bridge docks; the flo~ aroa is then
<br />reduced or the Channel Is cornpletely blockad. Thablockagecan
<br />produce Severe stage and velocity increases, often accompanied by
<br />br il.lge J"",,,~,,, "r comp I..t" fa II ur...
<br />
<br />Theuplandarnas in the Cherry Cr.."k basin contain dls-
<br />suct.oJ tOl'ogr"l'hi<.:roliu!"ithsteapstreamslonos. floodSilrc
<br />characterized by raoid rises, high maximum discharges, short
<br />durations,anJcomparativ",ly lowvoiumesoltotal runoff. \1ajor
<br />f load crests genordlly pilSS from II", uostream to tho downstr')i)m
<br />..~(jdS within n period of betweM 6 'to 8 hours. Flood penkS frOt"
<br />thunde~storm5 cover i nq >mal I "rOdS "re rap i d I y attenu" fed by
<br />
<br />lea olfocts have, historically. not boen a prObl<3mon
<br />Che,ryCr,l!tk,lcej..ms,ho"ev"',couldoccuri"thafuture
<br />"I tl\ouqh the chance of occur~cnCe of Such a phenomenon; s quite
<br />remote.
<br />
<br />v~i loy sforoge,
<br />
<br />Flooddamaqereductionmeasurlls-Thepossibllltyof
<br />ILJt"rp I 1"",1 <1"'m"qa~ in th<l LJppA~ (";hnrry r.r....k "'r"~ hil<; hAAn
<br />somc~hnt reduced by tho consl~uction 01 32 flood~~ter retJrdlng
<br />struetur"s, TheSoiICon<;orv"tion$arviC<lcOtl1,.,let"dconstruct;"n
<br />
<br />o' t~e~o ~'ruc~urc~ ;n 10(~ ns pa~t n' an OVe~ell nlnn a. ?~,,-
<br />
<br />sentp.d in t~o "..tershod work n Inns. Thpse 1>lnns wero thp.
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