|
<br /> . ,
<br /> 1
<br /> ,
<br /> ,
<br /> ,
<br /> ,
<br />~, ,1 1 I
<br /> , ,
<br /> I f".tl
<br /> , ,
<br /> of
<br /> ,
<br />
<br />
<br />i( J.
<br /> - (
<br />~ ~
<br />J
<br />.
<br />
<br />Table l. PClIk Discharge Estimlllc.~ - 1997 Flood
<br />Pawnee Creek and Pawnee O~crfl"w
<br />
<br />LOClliioll,.....,i'"'..'.'-;,..~._..__ "~~"---_....-.. Estimated l'cakl'low(cfs) <<--~.'
<br />Total Pawnee Ovcrllow into Sterling ju~t 3,800.
<br />northca~l(lflhcRivcrsidcCemelery
<br />PortionofPalmecOver!lowmtoStcrJing 2,500
<br />Between the Riwrside Cemetery and the Railroad
<br />embankment
<br />Pawnee Creek Mainstream U/S of HWY 14 65,000
<br />Pawrlee Creek mainstem at CR. 25 50,000u
<br />Pawnee Creek mainstem at CR. 29 45,000**
<br />
<br />,
<br />I
<br />I-
<br />
<br />
<br />. Assumos that th. Slerlll1g No. I Ouch IS full prior to Pawo<e Overflow peak dl-charge.
<br />.'Th;5va]uei,lessthanlheupst'oamv.luoduetovallcyW,,"geandflowallonuat'''n,
<br />
<br />Flows overtopped the BNRR at several locations. At the Town of Atwood, an estimated 20,500 cfs
<br />ovenoppcd {he railroad and returned directly to the SOUlh Platte River. Approximately 5500 crn
<br />overtopped the railroad just to the south of the Riverside Cemetery. Additionally, existing
<br />bridg.es/culverts allow.:d t100dwmers to go l.mder the railroad embankment. The Pawnee Creek main
<br />ehanncI bridge was estimated to have carried only 1800 ds, and the bridge approximately 1500 feet to
<br />the north had an estimated 500 efs. Location of these ovedlows is shown on Figure 2.
<br />
<br />Flow widths for the surveyed cross-sections across the Pawnee Creek !1O<ldplain ranged fnlm about
<br />1.600 lcet at the upstream end. over one mile at the dOWl1Stream end. The tlow depth in the confined
<br />ehanncI at the Up8tream arca wa~ over 11 feet, while the !low depth clu,er tu Town of Atwood was
<br />mueh more wide and shallow, with depths on the order "f 4 feet in the community ofTov.n of Atwood
<br />andadjaecntagriculturallands_
<br />
<br />The 100-year floodplain for Ih<: Pawn~'e Creek Ov<:rtlow I'Jr the existing channel conditions was
<br />presented in the report entitled "FllKJd Plain Information and Drainage Plan For ~and Cr~-ek and lh~
<br />Pawnee Ov~rllow At Sterling, Colorado" dated May, 1983 and prep:m:d by Charles Leaf and Resource
<br />Con,ultants. This hase engine<:ring data was used for the Community's Flood Insurance map, and also
<br />the ba~is for the damage analYSIS. Approxirnal<: limits of the floodplain ll!"e shewn on Fi~ure 7. Flood
<br />!lows for the IOO-yell!" llnod coming into Sterling from the l'avmee CR'Ck overflow were estimated to
<br />be 5000 efs. This compares to the calculated Pav.mee Creek ov~rf1ow peak of approximately 3HOO cf~
<br />duringlhe 1997f1ood.
<br />
<br />IV. !!YDROLOGY
<br />
<br />A detailed hydrologic ano.ly!;is was not completed as a par1 "f this report. The hydrology fmm
<br />prcviOlts reports were reviewed ,111.1 utiiiLCd in lhi, ,tuJy. Thi, feasihility slUdy was prepar"L'<l using
<br />hydrology infomllltioll taken from SCS. April 1992 docum<:nt titlcd "flood Plain Manag<"menl Study.
<br />Pawnc~ CrecK in i.ogan County, l ('t(lrMo. I he to!lowmg rabl,> stunmariz<:8 the flow 'niCS gl'ner..1ted
<br />ntvario",localions.
<br />
<br />Revised hydrology hassincebe~nprcpllJ"cdandwil1 bc used tor future design et1"orts. ThencW.'KHlr\:e
<br />lor the Pawnee Creek hydrology is the report titled "Hydrologic I Hydraulic AnalYSIS of Flood
<br />Mitigation Alternative #5, Pawnee Creek Overflow. Logan County. Colorado.. whieh \Va, prepared by
<br />
<br />
<br />
<br />
<br />(
<br />
<br />
<br />11
<br />
<br />100 YR FLOODPLAIN PAWNEE CREEK OVERFLOW EX, CONDITIONS FIGURE 7
<br />"M,L... _.1..(' I, 1~ i,/
<br />
|