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<br />Paleohydrologic techniques used to define tQtspatial
<br />occurrence of floods ;1
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<br />Robert D. Jarrctt , .
<br />u.s. (h%llcal SUM)'. /kJz 1'046, MS 411. 0,""'. CO 80111 (U.S.A.~ t
<br />(Recelv.d Sopu:mbcr 30, 1989; accepled atler revision January I 0. 1990~ 1
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<br />Jatroll. R.D.. 1990. Paleohydroloale technlqu.. usod 10 dellne Ibe .pa,ial occurrence: of floods. !3'f~ morphololY, 3: 181-
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<br />Ocllnlna the cause and.pallal charaelerillicl of floods may be difficult because oflimited S1teiOW and precipitalion
<br />dat.. New paIeohydtoloalr techniques tbat incorporale informalion from iCQmorphio, scdimcntol e,and botanic studies
<br />provide Imponant .IUpplClllClltal informalion \0 define bomoaeneo\l$ hydrOloaic reaions. Th~ bnique. also help to
<br />define Ihc spalialllrvClllrc of rainslonns and floods and improve te&lonal f1ood.frequency...' . The oceumnce and
<br />111. non-oa:u.Tence of paleohydrolo&!c evid.nte offloods, !IlICb u flood ba", aUuvial fans, and l~- provid. valuable
<br />bydroloale Information. The paleobydrologic researcb to dcfinelhe spalial eharamriSlics of fl' improves lb. undor.
<br />standina of flood hydromeleorololY. This .....rch .... \IUd 10 deline the areal e".nt and comr tlna cItaI..... lUU of
<br />fl.sh f100da In Colorado. Also, paIeohyclroloalc ovld.nce wu used 10 define lbe spatial boundari r the Colorado footb.
<br />iI1slC&ion In lCl'1IIs oflbe meleoroIoaio caus.: offloodina ancl eI.valion, In I.neral, above 2300 iflrpeak flow. atll caused
<br />by snowmelL Below 2300 m, peak flows primarily atll ClU$Cd by rainfall. The foothill. ~ hu q upper elevation limit
<br />:! ,. or aboul 2300 m and a 10"'" elcvalion Iimil of about 1500 m, ROJIonalllood.rrequency es1lm~tll! tIuu Incorporate th.
<br />" paIeoh)'clrolOlit informalion indicate thaI the Ilia Thompson River flash f100el of 1976 haela ~rrence In\erval oCap-
<br />proximately IO,ooo)'CIl>- Thil eonlralts markedly wiLlI 100 10 300 yea" determined by Ulill/l~<:!J'venIlOnal hydrolOllic
<br />Inal)'$O$. F100d-dlscllaflO esl1malea bosed on ralnfall-runoll'method.! in the foothills of ColoraKrault Illlarpr valuu
<br />th.n tbose OIlimated whh rcslonal flood-frequcncy relation.. whicb arc baseel on lona-Ienn SlrCalll\ow dOlL
<br />Preliminary hyelrololie and p.lcohydrolo&!e ...earch Inelical" that intenso rainfoll doe. not ociat hllher oIevations
<br />In other Rocky Mountain 110... aDd that the bightS! clevatlons for llIinfall'producins floods ..~ latitude. The study
<br />results have Impllcltions for flOOdplain manllloment and desian ofhyelraulit .Iruerures In lhe m?' tala. of Colorado and
<br />other Rocky Mounlaln States. : ~
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<br />Otomorp/lOlolY. 3 (1990) 181-19'
<br />Elsevier Science PublWtera B. V. Aml1erdam - Printed in The Netberland.
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<br />ABSTRAcr
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<br />Introduction
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<br />floods in the foothills re~n is uncertain for
<br />floodplain managemcnt ,aid for design of hy-
<br />draulic structures on floodtlains because of the
<br />lack of hydrologic data..~ause of the poten-
<br />tial adverse effects offlo there is a need for
<br />a better understanding of ood proccsscs, cs-
<br />pecially in mountainous iffions.
<br />In 1976, a catastrophiFfash flood occurred
<br />in the Big Thompson RJ'\- in thc foothills of
<br />the South Plattc Ri vcr b : of Colorado (Fig.
<br />I), This flood resulted fr m as much as 30S
<br />mm of rain fallina in_a.: w hours. The peak
<br />discharae of this flood w. 883 em] 5-1. Thc
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<br />In Colorado, as wcll as in other Rocky
<br />Mountain statcs, annual pcak streamflows are
<br />caused by snowmelt at hiiher elevations in the
<br />mountains and by rainfall at lower clcvations
<br />in the plains and plateaus (Jarrett and Costa.
<br />1983,1988). Thcarcalclltcntorthctransition
<br />region, tcrmed the foothills region, bctween
<br />snowmelt- and rainrall-produccd peak flows
<br />has been difficult to delincatc becausc of lim-
<br />ited streamflow and precipitation data. Risk
<br />assessment and thc impact on humans from
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<br />Elsevier Science Publishers B. V.
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