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<br />
<br />FLOODS OF 19t1<'-, IN THE UXITED STATES
<br />
<br />SOUTH PLATTE RIVER B.....SIX, COLORADO,. ~rL-XE 1965
<br />
<br />P~':i:
<br />Uvv
<br />
<br />tiO-YE'ar flood. Channel storn.ge and other 10:';:-3(';5 ;'('(lurell {he flood
<br />peak until it was Jp~s than thl~ 2.,-)'('<\1' flood at ~~l!:~ll Platt\'~ XdH'.
<br />
<br />?,raphs, and map contour' are u::;.ed to esbblish the DOlllldarif>.'..; of the
<br />arl'a illUlu.lat.ed hy the floods. Flood-crest profiles and the ~'()IT{,::='po!ld-
<br />ing- nlaps of inundated areas for several reaches of the Sonth Platte
<br />Hin"r between the month of Plum Crpek and Adams ("ity, two reachc::=.
<br />of Sand Creek from .\urora to the 1110I1th, ,uul the l<nq'l" .f- llliJ{'", of
<br />Toll Gate Creek are presentl>d on pJat€s:j and-1.
<br />The pl'ofik~ and maps ,He ;Hlaptell from data ('ol1ccted and fu!'-
<br />ni~hed by th(' 1-.~. .\rlllY ('01'1'.':; of Ellgill('(>I'.;;;, 1)t,t:\i]~ (,Oll('l'r11ill;! TIlt'
<br />profiles :md m:1p:-o; are on tih, in tlw Corp~' di~trid ofli('e. (hll:lha~ Xebr.
<br />
<br />DETERMINATION OF FLOOD DISCHARGES
<br />
<br />The disch:uge at a stl'C',un-gag-ing station is eomp'..<ted from a stage-
<br />dis('har~c re!:ttiDll. The' ~t:lge i;'.. out:l.tllC'ct frml'l. a. \\"~'~:\'l.'-stt\b~' recorder
<br />de-signed to prO\-iof> :l continuous record of :-;.tag-c. If the \Yater-stage
<br />recorder malfunctiolls or i~ dalllag-ea by thL' Hood. :':i;.dl-\yater mark::;
<br />and direct readiIlfYs on a llo11r('('ording g<1ge are 11::-:\.'..1. The discharge is
<br />generally measnred by current llleter, but indirect 1l1.cthods ~n.e used
<br />sometimes. The discharge llll':lSUremellts; at known ~tages; are lised to
<br />compute the stage-discharge relation from which discharge may be
<br />~. . i' ..
<br />caicuiateti. lur allY ~on'n srng'{',
<br />Short extensions of the stage-discharp:e relation \1,\)o\,e the highest
<br />C'llrrcnt-Hlf't('l' nwa~\lreme!lt. C,l!l be m~HIe by l!~i!1g the results of slope-
<br />conyeyance studie3~ by using other 11w:\snrahle hydraulic ftlctors, or
<br />by logaI-illlll1 ic piotting. LOlli! extellsions of r~'1a! i{):l:3 were defined by
<br />
<br />FLOOD FREQUEKCIES
<br />
<br />.At many locations ill the Hood area, the floods of .Tune 1065 ('x~
<br />I'eeded t.he clis'rh:n.ge of thp ;}O-y.enl' flood by 5eYE'rnI orders of mng-nituu.;:
<br />and probably ex('eeded the discharge. of the 100-year Hood at se,-eral
<br />locations. The trne frpqUPllcies of floods of tlwse magnitudes ('annot. ue
<br />det.ermined from the present records~ whi('h are l'eIatin~i'y ::::.hOI~t.
<br />Tho flood-fn'CIuency report C\Inttlwi, HHiS) for the Hood urea ill
<br />rhe South Platte Rin:>r bflsin has relations for one region, three ]lyclr{)~
<br />logic areas, and the main stem of the :-3outh Platte Ri,-er, Coal, 1..0ne
<br />TI'ce, alld ero;" Creeks are in Oi'H> IIJ'drologic area, and the peak dis-
<br />('harges in .JnDe. 1065 on t.he...~ streams were, respe.cti\'ely, 5.0, 2.4, and
<br />0.8 times the discharges for the 50-year floods. Only a sma]] part of
<br />tho:;. drainnge. bf~sir!. of ern'.'.' Creek contl'ib:..:..t.ed n:"llGff tG this flovd;
<br />hence, the lower ratio.
<br />Plum Creek is in another hydrologic area, and the peak discharges
<br />ill 1965 on East Plum, 'Vest Plum, and Plum Creeks were, respecti\'ely,
<br />-14,11, and 21 times the discharges forthe 50. year floods.
<br />Cherry, Sand, Kiowa, Bijon, and Beaver Creeks are in the third
<br />hydrologic area. The relations of the 106;') peak disC'harges in this are.1.
<br />to size of drainage area and selectf'o recurrence internlls are illus-
<br />trated in fil"ruro 11.
<br />The points plotted for Kiowa Creek snbwatersheds Q-51 and R-3:j
<br />are estimates of the maximum 5-minute inflow to the reseryoirs. The
<br />highest ratios to the discharge of t.he 50-year flood are 11 for Ea~t
<br />Bijon Creek at Deer Trail and 9.0 for Bijou Creek near IYiggins.
<br />The 1965 flood peaks along the South Platte Ri,..r are plott€d in
<br />figure 12 against miles nbo\"e the mouth, and ('UI'\'es for tlH' 25-yea1'
<br />and 50-year floods are shown. The recunence inte!Tals of the peak
<br />discharges, mostly causeel by the Plum Creek flood, are much greater
<br />thau those for the 50-year floods between Littl€ton and Fort Lupton.
<br />Flood flows at Kersey aneI "'eleIona were less than the 25-year flood,
<br />hut the tremendous discharae from Hi lOll C'l'C'f"k boostpn tlu> l)p~k
<br />discharge in the South Platt; Ri,'cr at llalzac to -1.1 timesihat-of the
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<br />lnstantane:::....'" peak discharge _
<br />x Instantane:::o..Is peak outflow
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<br />. Maxtnlum S-mmute inflow
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<br />CONTRIBUTING DRAINAGE AREA. IN SQUARE ~:lES
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<br />1000 3000
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<br />FrorRE ll.-Rf'lntion of I}('uk discharge to size of drainttge basin for Cherry.
<br />SiinJ, Kivi:;;a, Bl.juu, ami Bt"a \"(~r Creek~,
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