<br />The mOre cOIl'iI1on flood In the C1!<::he I~ Poudre River study
<br />reach I s that '~h IC1) exceeds rho channel capacity 01 about 5,1100 cub ic
<br />feet per second bClt is Sr13 i lee than the I ntermedi ate R8<1 iona I F I cod . T~e
<br />(lven'g'" annual reJk d i:Jc.~or'Je frCl'1 all records at tho Fort Coil ins <1ago Is
<br />4,~38 cub ic fod P(,r 5<lcond, The Stdnd~rd Project Fiood is not the I~rqest
<br />flood ~hat C"n occur in t~" study r"ad, ~ut the ~rotJ&>ility of lar,?,"r fl<l<'lds
<br />becomBS increa,ingly rarote.
<br />
<br />FUTLREFLOODS
<br />
<br />T,,[)1,,4
<br />
<br />Two largo potentia I I loods '~ere devel<lred lor the study
<br />reaCh inordertoassosstnefloodhalardt"ere, This"asdonebva
<br />statistical analysis ot gaging records 1!nd the use o' routing techniques
<br />for thB reacnosbetl/con tho gages. Oneflood,thBlntermediateRo<jional
<br />Flood,or 10o-yeJrllood Is <jBnerally accented by the publica5a minimum
<br />limit lor application of local regulations. Theother,theStar>dardProJect
<br />Flood, isli:lrgerar>drepresentsareasonallleupper-Ilmlto!expoctedtloodin<1.
<br />
<br />POTENTlA.tFLOOOPEA.KDISCfl;\.f1n;:S
<br />CACIlE tA PO'J()tlE RIVE~ AT FORT COlli US
<br />
<br />Lccatlon
<br />
<br />Int~rmeJI~te R09lonal
<br />Floo<lPe1lk
<br />lisc~"rqe
<br />-----c-.T:s-,~-__.h-
<br />17,400
<br />16,200
<br />19,700
<br />19,700
<br />
<br />Upstre~m II",it 0' Studyl1each
<br />ftbove mouth 0' Cc, Creek
<br />'.leI"" MOuth 0' Dc, Creok
<br />
<br />,
<br />I
<br />I
<br />
<br />[lo,.,nstrea", I ;mlt of Stu~y Reach
<br />
<br />Intormediatel1ej]lorll'l1 Flood
<br />
<br />A d Ischarg9-froq~ency curve "as developed by a st"tlstical
<br />anal ysis of stream! 101'1 records ~nd ;>~st floods In the study reach: thus
<br />dofining the magnitude of the Intermediate Regional Flood. The Intermediate
<br />Regional Flood Is delined 3S one that occurs once In 100 years on the average,
<br />alt~gh It could occur in any year, The Intermedl~te Reqlonal Flood peak
<br />d ischargos at sever" I key points I n the study reacM are s!la;n in t~b Ie 4,
<br />
<br />Frequency
<br />
<br />Standard Project Flood
<br />
<br />The Standard Project flood results Irom a storm of ,uch
<br />magnitudeth<it It isdifficulttoiissl<jna frequflrlcv to the recurrence.
<br />It is defined more CO<n?letely In tho Dlossnry. The Denvnr ar~a floods
<br />ot 1965 and thc 116pld City, South Dako~a f Ic:o<: of June 1972 ~re 'Jxamn Ie,;
<br />of su<,:n ~ fl()('>(i, Tn" Sten<ii'trrl ProJ<>et Flmd pf'ak di5Ch~rges at several
<br />point51nthestudyreacharesho.;nint.Jble4.
<br />
<br />1{.1~~rd, 01 Large r loads
<br />
<br />St~n~~rd rro.ied
<br />Flood re~k
<br />I'Jlschar'1e
<br />-C-.T,-s-.~--.-_.
<br />43,700
<br />40,000
<br />60,000
<br />60,000
<br />
<br />Hyd~au I Ie stud lo~ wcro "",de to dnt"rmi"e the t lood haldrd
<br />presented by the I nter",edlate l'le'1 ion~ I and Star>dard Project Floods through
<br />tho study reach. :honnol ond ovorb~'k cond Itions were represented t>y
<br />bridge and va Iley cross ~ectlonz madB In 1972. "actors contrlbutln<j to the
<br />tlood h.1Wrd include extent 01 oraa flooded, flood ~epths, oost.-uctlo"s to
<br />flood 110.15, velocl1los of 11001 f 10. S, rate of ri,e of s~roarn leve I, and
<br />duration of floocing. flood dat""Jagc~ ~€ncr3111' incre~se as f lood dept~~
<br />Ilnd voloc;tle5 i nCr<:!aSe, C1J~fructio"o, to I I ""0, tend to ceus<:' '~at"r lev,.15
<br />to riSB.
<br />
<br />"
<br />
<br />"
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