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<br />The Haod discharge is reduced liS the flood",.uer~ spread out to fill
<br />th" broad \r~lley. Irrigation dlv"rsion" from ehe C~che h I'audre Rlv~r
<br />"'ere not incl<lded in the ilnal/~1s. Halligan Re~ervoir, on the )lorth
<br />,ark Cache la Pa"dre Rtver, aha reduces iloael peaks as they pa""
<br />through its "pili"'ay.
<br />
<br />Table 6
<br />Potent1alFloodPeakDlscharges
<br />Cache La Paudre River Basin
<br />
<br />Drainage
<br />Strea", and Discharge Location Area
<br />(sq."i.)
<br />
<br />North Fork Cache la Paudre River
<br />
<br />Upstrea~ from Halligan Dam
<br />Do",nstrearo fro~ Halligan Dam
<br />Upstrea~ fro~ Lone Pine Creek
<br />'ownstrea~ from Lone Pino Creek
<br />Atllouth
<br />
<br />!.oncPineCreek
<br />
<br />At Mouth
<br />
<br />Cache l~ Poudro River
<br />
<br />opstre~rn irom Poudre Park
<br />'o",nstream from Poudr" Park
<br />Upstream fra~ confl"eoee ..ith
<br />North Fork
<br />At Bluff l1ne
<br />lIpstrea" fro~ Dry Creek
<br />Da~nstrca~ from Dry Creek
<br />Jpstr~a~ from Boxolder Creek
<br />DQ~nstrea~ from Baxe1der Creek
<br />"pstr~a~ frvrn Latun Dr~w
<br />D~wnstream fra~ P.aton Ora'"
<br />At:1outh
<br />
<br />10-year
<br />(~. Ls.)
<br />
<br />m
<br />
<br />3,440
<br />1,980
<br />2,020
<br />2,510
<br />2,490
<br />
<br />'"
<br />m
<br />%
<br />
<br />"
<br />
<br />1,260
<br />
<br />385
<br />409
<br />
<br />4,960
<br />5,110
<br />
<br />",
<br />1,055
<br />1,102
<br />1,19;
<br />1,'245
<br />1,537
<br />
<br />5,230
<br />7,000
<br />8,400
<br />10,100
<br />M,OOO
<br />17,700
<br />2,650
<br />3,550
<br />3,100
<br />
<br />.A,_
<br />.,""-'
<br />1,875
<br />1,~qO
<br />
<br />27
<br />
<br />100-year
<br />(c.f.a.)
<br />
<br />14,980
<br />9,260
<br />9,800
<br />12,170
<br />11,830
<br />
<br />4,810
<br />
<br />16,,00
<br />17,320
<br />
<br />17,700
<br />17,400
<br />16,200
<br />19,700
<br />i6,600
<br />28,500
<br />6,i,00
<br />LD,loo
<br />~ ,400
<br />
<br />Flood Peakin8 Time. In addition to factors such AS flo'" dupth and
<br />velocHy, the peaking time of Jlo"d runoff affects the nat"re of th~
<br />floodha"ard; the peaking ti"'e of ftood runoff lsthe time frotll the
<br />runoff~praducln8 r~iofall to the tl~e the flood rcaches its ~a~i~urn
<br />discharg". Also ~eaklng time is genHally related to duratlon. It
<br />~o"ld be e~pected that a rapidly rising stream ",auLd h9~e a rapid fall
<br />and a short dur&tion of flooding. Table 7 indicates the peaking time
<br />of floods from mountaln tainstorms at ~~rious locat1ons 1n the basin.
<br />It also indicates the time fro~ the start of rainfall runoff to other
<br />
<br />flOod e.ents pertinent to flood warning.
<br />
<br />SOO-year
<br />(e.f.a.)
<br />
<br />I'eaking times in ehe mountains ",ere obtained by the MITCAT model.
<br />Peaking eimes in the plains ",ere developed in the follo",ing mnoner.
<br />Tne ~nking time of thn ~nin stem near the confluence with the North
<br />Fork of the Cacne In Po"dte River is taken as a starting point. Thia
<br />was developed by the MITCAT ~odel. Do"'nstream fro~ the confluence, the
<br />MITCAT model was not used. A. aynthet1c flood hydrograph fo~ the LOO-
<br />yea" fload ",as routed downstream. The time at WhiCh this hydrogtaph
<br />reached various points do"'ostream "'as noted. This waa added to the
<br />~..akiog time of the maio ste~ flood near the edge of the mouotalos (the
<br />car.fluencc ",ith the :lorth Fork) to o!lt"in tho eotnl ~e"kin8 ti::lc.
<br />
<br />32,120
<br />22,790
<br />22,"50
<br />2i,"7iJ
<br />26,940
<br />
<br />Q,510
<br />
<br />31,870
<br />36,220
<br />
<br />Floods ~ere assumed to orlgioate from the main ste~ aa ~o"th For~
<br />floodsnreslo"'er.
<br />
<br />37,040
<br />31,000
<br />23,800
<br />2B,200
<br />24,000
<br />42,000
<br />l4,6Uu
<br />19,000
<br />11),800
<br />
<br />The peak1ng time of flood r"ooff is more graph1cally illu.trated
<br />on Plate 3. At tho extreme io",er end of the basin, peaks can occur in
<br />L day or ~or~. In thn mountains, ~inor tri!lutaries ~y have ooly an
<br />hour or leas fro~ rainfall runoif to flood pea~.
<br />
<br />~HYSICAL C~\RACTERISTICS
<br />
<br />Stream and Valley CharacteriHtlcs. Th~ slope of th~ Cache La
<br />Foudr.. 'th'er .w~r"ges ,ro," 3 to to feet p"r '1110 >!CrClSS t~e pL1in..
<br />1'0.. d~pth of the Cach~ 1a Foudr,. River ~hannel [II the 1'1.110" rdoges
<br />,ro~ ap~ro~i~tely , to ,4 fe~t ~ith the av.~aRe h.i~g ahou, !0 feet.
<br />
<br />"
<br />
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