<br />The more COffJ'lOn flood i[]theCache la f'oudre River study
<br />reach i5 that -<1M iel' exceeds the _c'1annol c<l~,1cTty at ~bout ),(100 cub ie
<br />fea~ !,cr second but I~ ""1aller ~han the Inter,:",dia~e Reqio~ai flood. T~e
<br />av"r~80 ilnnUa I p""~ d i5chDr<)e f,-O'" D II records at tl10 "o:-t -:'";011 I 05 1aqo is
<br />~,8YJ <:u~ic Ipet opr ';r"~",,d. Th" ,tMh,;",r~ Pro.;A"~ FlOOd is not ~he l"rQAst
<br />"Iood -n",t c~~ occur in the ot~dV reac'C_. but ~'H'-oroodlilitv of 1"'-'l'Jr floods
<br />I)ocomcs irlCre~sin~ly n...,<:rte.
<br />
<br />FUTU'lEFLOO::;S
<br />
<br />Til~ I c ~
<br />
<br />T~o large potential / loods ~ore develolJed I()r the studv
<br />reach In o;dc; to assess the t I ood hazard ~he'-o. T~ i s wa ~ done b V a
<br />stat i st iea I ana I Vs I 5 01 g~g i ng record ~ a rid the u5e of rout i rlg techn i QUOS
<br />lor the re,lches betweGn the qilqe5. One / load, tho Intermed i~tc flo~io~a I
<br />Flood, Or ID)-yoar f 100<1 is qeneril Ily ilecanted ~y the rub I Ic ilS a ",inlmum
<br />I imit lor ilpp I ]catlon of loca I renu lations. The oth"r, t~" St"hJard rrQj,,<;t
<br />F I oed , is larger nnd represemts a re"sonnb Ie unpar I le'l I ~ of cxpoctcd f I oed I n(l.
<br />
<br />e>o:-ENTIAL FLGO) PEAK )ISCIIAf\CES
<br />r.A~IE LA i'OLJ:JRE RIVEr< AT ForT COLLI~:S
<br />
<br />LC:<:dtlon
<br />
<br />l"t~rMAdinte Regional
<br />FloodPeilK
<br />_~~.1J.s.::.11.a.:iJ.()______
<br />c.t.s.
<br />17,400
<br />16,200
<br />19,700
<br />19,700
<br />
<br />I nterm6diate Rogional Flood
<br />
<br />Up"trn;,m lirnltotStudyn""ch
<br />."!Jove r'lCuth of DrV Cr<WK
<br />8dQ,ol O\Outhot DrVCreck
<br />Do.;n5tre"",II",it-oIStucyReach
<br />
<br />f, d IsCharge-lrequerlCy Curve was develop"d by a st~tlstTca I
<br />an~ lysis 0/ streile'lf 10; records and pilst floods In t~e study reac~; thus
<br />defining the magnItude 01 the Intermediate Reqlonal Flood. The Inter~&dlate
<br />RogionalFlood isdctinedasonethatoccursollce In IIJGvearsontheaverilQe,
<br />although It could occur Tn any year. The Intor~edlate Reqlonal Flood peak
<br />discharges at several ~ey points in th~ study reach are shewn In t~blo 4.
<br />
<br />Frequency
<br />
<br />Stand,lrd Projed Flood
<br />
<br />The Standard Project F loed resu I ts from ,~ storm of S'lCh
<br />_':1agnitudetnatIt isditfi<;ult tOlJssigndfr",quencytotherecurro'),jCO.
<br />I t is cot Ined "1Or(l complete IV in the Glrlssary. The Dt'nv,)r "r"", t lo"d~
<br />of 1').65 "lid tl", Rapid CIty, South Dakota flood of June 1972 are ()>(~"ml,,<.
<br />otsuChatlood. TheS1"andilrd Project Flood reakdi!;ch1lrqesilt5evor,,1
<br />points In the s~u<!v reach are sl1CW n In tab Ie 4.
<br />
<br />Ii,,~~rd~ 0/ Large Floods
<br />
<br />St~r:d~rc "ro Ie<:t
<br />F 100<.1 ro~~
<br />Oiscrilrqe
<br />~-.-r.~~..~-_.- --
<br />43,7'10
<br />40,000
<br />60,00G
<br />liO,OOO
<br />
<br />IlvdrnJ I ic 5t,," ,,.'s w or~ modo to dot"rrr_ i~" too t I OO,~ r"'z"rd
<br />pre5cptcd by tl.e Int('r~c~l:lto 1~"'!1lonal and St~nGard F't'"o:E'd "Ioa.j~ th~OUq"
<br />t~,] stuc:y :-oact.,. Cro,ono I Clod overbank cond itio15 ~'er" re~r"sCtn+ed by
<br />bri ,k]<' and va I I<,V cross soctlons mark ; n 1'l72. Factors ~"ntr;hLlti nq to the
<br />flooa Mz~rd ixllJde exten~ 01 ""e~ tloo1ed. flood d""th~, oo5tn,~t;(.'f\5 to
<br />t load t 1"",., vO loci tie~ of f IO<YJ 'fa" s, n,te cI risE' r;f strI')C"" lev>> I, nnd
<br />dur"t ion 01 f 100<.1 i "'1. r lood dana'Je~ 'Jt:nera II y i rrcreaSe a'; f looe Mcrthr
<br />and veloci ties In"reasB. CbstruC1 lor~ f'o '-Icws tond to C.'lU1r ~at',r lew'l,
<br />torl1C.
<br />
<br />'P
<br />
<br />"
<br />
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