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<br />the pro~able maximum flow for th~s stream. R '; ,all over theBl~ck
<br />Squirre~ Creek watershed produce~ a peak f ow ~:, ,.~.,,14.,l'OOO c. f. s.' ',' These
<br />two smap streams produced most ~f the flo d I ,r~he Arkansas Rivllr from
<br />Pueblo \:0 Las Animas. Jimmy Camp Creek wa tliiprimary,contribul:orto
<br />the flobd on Fountain Creek whicl\ resulted in!~he flood.of record at
<br />Pueblo.! The contribution from B~ack Squir el lQt~ek caused Chico'Creek
<br />to produce 50,900 c.f.s. at the mouth. Th' CI!~~o Creek and Fountain
<br />Creek flows combined to give a peak of 102,000 !e.f.s. in the Arkansas
<br />River a~ Avondale.
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<br />361. FLOOD FREQUENCY ESTIMATES. - Exc edenc;efreqllencies of, floods
<br />for exi$ting river conditions and conditio s te~ulting Ifrom control by
<br />Pueblo Reservoir were prepared to permit e aluation of!benefits Fredit-
<br />able to the project for prevention of floo losses . The princip~es used
<br />in the computation of flood probabilities ere based on procedur~s of
<br />statistical analysis. Since flood ,losses lin the Arkansas River subbasin
<br />from Pueblo to John Martin Reservoir are mpre closely related to flood
<br />peaks than flood volumes, only peak frequencies were developed.
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<br />'37. Data used to develop the freque~ly curves from Pueblo ~o Las
<br />Animas were obtained from records at six 5ain stem gaging statio~s' and
<br />from Fo,untain Creek at the mouth. These sltations on the Arkansa$ River
<br />were at Pueblo, Avondale, Nepesta, Fowler, La J'unta and Las Anim~s.
<br />Data from records at gaging stations were extended and adjusted rorad-
<br />ditional drainage area to develop peak fr,qUency curves below all of the
<br />major tributaries. The frequency relatio~ship for a typical reach down-
<br />stream from Chico Creek is shown on plate 6.
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<br />38. STANDARD PROJECT FLOOD.- Runof from, the June 1921 storm was
<br />determined to be of standard project floo mag~itude. For the original
<br />studies of the flood control requirements at Pueblo Reservoir, i~ WaS
<br />determined that an increase of 50 percent in the 1921 flood hydrograph
<br />as it occu,rred would be equivalent ~o the standard project flood'. I)uring
<br />subsequent studies for the Repo'l't on Revie/JJ Su'l'Vey for FZood Controt and
<br />AZZied Pu'l'poses.A'l'kaneas River and Tribu 'l'ies above John Martir ~.
<br />Cotorado. it was further determined, from a transposition of the June
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<br />1921 storm, that the standardpro)ect flo d voliume would be about 50
<br />percen~more than the June 1921 flood as t ocqurred.However, ,thelpeak
<br />dischax;ge from this transposition would b abo~t twice that of t~e ~ctUal
<br />flood Or 170,000 c.f.s. The standard project,floodhydrograph 8:t Pjleblo
<br />Dam with a volume of 140,000 acre-feet an. a peak discharge of 1;70,000
<br />c.f.s. ,is shown on plate 5.
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<br />39. DESIGN FLOOD.;' The maximum fro d of record ,at Pueblo :occurred
<br />in Jun~ 1921. The flood had an estimated !peak discharge of 103,.000 '
<br />c.f.s. ,and a volume of approximatel)'ilOO, 00 acre-feet. Pollowing this
<br />flood, :the Pueblo Conservancy Districii:co structed a floodway through
<br />the urban area which is capable of safely discharging 110,000 c.if.s.
<br />with a ;minimum of 3 feet freeboard. To s pplenient the floodway,1 the
<br />Pueblo Conservancy District also construe ed Barrier Dam, a detention
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