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<br />~N1aiEQRbt;OGJC'ALIIII~SPECTS 05 THE BIG THOMPSON
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<br />~j!ii; 'FL:ASHFbOOO OF 31" JULY 1976 : rn ;
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<br />'\;Ro~et't~. Maddox, FernandoCarac.ena,'
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<br />., "':I;,:e.t;R.-:tiOJi~; and Charles F. Chappell
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<br />AbstraC!i:;!\Il<ll~se~~anqd~scriptiqn~ of Ineteo!ologic,!l c,'onditid\):s,,;that p~o-
<br />d'r~ed\~l'1 dev'!slal,in,gflhshf]ood in thtl.Big:rhoIl,'pson CanY9n on ':31 July 1976. "'~ jl;
<br />.are pre1ef)te,l:Th", ~tqrm:,dev'lIoPtld \\,henstrong lS1w-lev~1 e'lsterly wiiIds to
<br />. tb~~:em' pf;lpof"':Jr'op tPt,sheaa)llQj$t"co~ditipnally unstab.le aiwla$s.upslope
<br />illt)) the:Ei:c:1I1t~ange;.Of!he.Ro*ckY;'M9~~It(lilfs.. Orogniphic. upliftrele"?<id:th. e;,
<br />'l'!JA-......., ""l"l't%'-~I"""",u~~'h %'1" 'd' . "1'1
<br />i;;s:l_1l1r':'~,(1,t?!~~JnS'7l ,~ll,).~r,~tl.1?-(~ .~g.~~t:~ol!~l?,sout,e~lst,er ~wln .?at)ste~pn~J1~le,,~
<br />ill %;)ll~VJld ~ stG];m(::(lIpple~ (O;,Enn'WFnearly statIoqa~y :o~er the footn.Hs: 1/1
<br />,,' J>~i~ . ,trW:~~~pt'2er.~,jti\}~li~'~lst<1i]">lt .I.:}'idd}e-ahd\ll'\pe-r l~yels"v~ry ..
<br />JpX;;'. . ,}l"S~S>!lI1U';l<.sh~jltW ~I$edlllpd(affw.struqtlm' contnbuteg.\\l,.,lJugh
<br />.W~<jJeit:;l~i~i!,.efllc;j~~~,~leteor~rQmcll)fsol1di~~o~&.~p"t' Plo~It~~d. the. Big;
<br />Thompsgli~m(j R".v'd9t>?mr~ l1opd~ffre somn'~eUand};hGwn to haVe IJi:ep
<br />v;;n-!'Slllli!,lj', A"~ett9f W'et'e'lllx)lo~i1;a~~aition~ is,cleHned fUr the,pulJjostl;Of
<br />A~l1tifyilf}.\;thepd\e'ttti<ll /):>-y I1asH;I1'f)a~ in Frol1t Kmge canyons.,' I)
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<br />1. Introduction
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<br />During the evening hours of 31 July
<br />1976, a destructive flash flood rushed
<br />through the Big Thompson Canyon west of
<br />Loveland, Colorado, V,S, Highway
<br />34--the primary route into Estes Park and
<br />Rocky Mountain National Park-parallels
<br />the river; the canvon had been extensivelv
<br />developed with husinesses, motels, and
<br />campgrolmds located along the scenic river
<br />bank Larimer County officials estimated
<br />that between 2,500 and 3,500 people were
<br />in the canyon when the floGd occurred
<br />(NOAA, 1976), and the toll was heavy: at
<br />least 139 people were killed, and property
<br />damage of about $35,5 million occurred,
<br />The storm produced very heavy rains
<br />in a narrow band along the Front Range
<br />from the Big Thompson drainage north-
<br />ward into \'Vyoming, Maximum amounts
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<br />exceeded 12 in (305 mm) with much of the
<br />precipitation in the Big Thompson drain-
<br />age falling during the 4 h from 0030 to 0430
<br />Greenwich Mean Time (GMT), (GMT is
<br />converted to Mountain Daylight Time by
<br />subtracting 6 h,) Significant flooding and
<br />damage occurred in Colorado on the Big
<br />Thompson and the North FGrk of the Big
<br />Thompson River, within Rist Canyon west
<br />of Ft. Collins, on the lower portion of the
<br />Cache la Poudre River (Poudre Park to Ft.
<br />Collins), and on the North Fork of the
<br />Cache la Poudre Rive" Flash flooding was
<br />also reported over areas south and west of
<br />Wheatland, Wyoming,
<br />Fig, 1 shows Colorado and surround-
<br />ing states and identifies landmarks and
<br />towns that are referred to in the report.
<br />The Big Thompson drainage, areas affected
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