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<br />
<br />Th~ most r~c"nl nand in lh" Craijt an'"
<br />occurred alunlt" tn,' Yarl1~a Rin'r in April
<br />197,1. Rapid <nowmellllen~r;'ted by unseawn-
<br />ably warm w"alh~r wa~iLuj.(menl~d by rain on
<br />are"~notco"eredbysnow!)('I\\"ecnSle"mb(ml
<br />"prlt\;:~ and Craij.(. Thert' wa<, how"H'r,
<br />m'~li;:ilJl"flooddama"cintheCrai!(art'aand
<br />rcturnin;: cold weather sharply reduced the
<br />
<br />rat~ nf 'nnwmelt. Perhap" the mo't critic~1
<br />;itu~linn \\'a< at lllc mllnlnpal water IJlanl,
<br />whkh was s"rl"Ounrled by f1oodwatc'r. hut
<br />protettcd b)' ha>til,. built rlikt" Railroad
<br />sc""i", 10 Crail; wa.cut off (or morc than:\
<br />wcek by badly dllmaged t,'ack in se,'eral
<br />lo<:ati~ns ktwel'n Crail;amll'hippsburl;.
<br />
<br />~',~."" t 1, Y,mJ'" Riw, t:.."In"w<""'rt,wo""rIYQICr~'~, Aprii~J.:ll, 1974.ll'how~c.rm'!Q' ",o...io<",",,,,,,),o!'o,' Muff.!
<br />C"ll'\)" l'lannin~ Department.1
<br />
<br />FLOOD DAMAGE PREVENTION
<br />
<br />Fullo"i"...- lIw 19,17 n'~1<1 i" emilo[, Vorlifi.
<br />cHttOn C,vek "'I'" im!Jroved und~r ,'mer~"ll"V
<br />",'pair and rt'sloratiol1 aUlhority av~;I>lbll' to
<br />the Corp~or Enj.[ine"r;;. TIl~ work Nttsi,teduf
<br />eutt;nJ.( a now. stnlil'htchan"d ," thr lowf'r
<br />,','aoll ~(Ihr ~r('"k: "trnil'htl'ninganrl impro".
<br />inglh,' creek upstream fl"Om Illene", ehan"~]
<br />oection: and pro"'di"l( I"w, 3poiltYlle I",""-'s,
<br />Thi, work, plus 3ub.tantinl n"t~rn] chan"d
<br />i'npfov"mcnt,bJ('t"incrc'asedf\O"'wloeiti~s.
<br />has mnt<.'I'ially ,l<"-'rt'a~t'd i"~ jam I'fobl<'rm.
<br />kfjHn1sth"t h'\\"~(Jo:"urt'ed in rN'entyea,."at
<br />'I <'<'W""liltt','ro,,,in,,ufl,tr,'nmfrom lliv:hway
<br />.IO"nuatth,','ailroadcr",;sinj(dowMt,'eam
<br />from the hij(hw,-"y hHve been remo..~d by city
<br />ami railro"d mainlenmw" e...."'s. A"ide from
<br />the .'merg~""y work d"Sl'rllK'<1. which wa,!
<br />'''-''''I'k-ll,l ,n l~qll. thrre are no formalized
<br />fl,,,,,ll'ontrol projd'l.<hnvinl(andfi'tl in th.,
<br />
<br />,tt"l) ar~,,- CUltll'J'ehens;w vlans eumpri,inl'(
<br />a 6IJ,OIIO "ere.fOOI floodeont'Xll "'''''rvoirtlr
<br />Ie,",,,, eon'trt"'ti",,, ("nantlel impro\"{'mt,,,t
<br />lI'ork. and ""placellwntofobstructivebri<l)l6
<br />have been ~tlldied a'''! I'mIWl<.,rl hut never.
<br />"uthori,,'d,
<br />The Cily of L'l"aij( and Moffnl Counl" "I""
<br />eligible for flood in'll!'lUtt'e und'~r th" ~mer.
<br />I'eney ph""" o( th~ ;\ation,,1 Flow In,~rance
<br />hOllram, To ma;ntai~ e1il'ibiJlty. th~ pru.
<br />I(,',un r~'luirl'" adoplion and .'nf')fo"ment of
<br />lanrl uw nnd control moa<ur~,;; that I(uidt'
<br />futur~ me and d~ve]opment of flood prone
<br />"rea" in ~ueh a way that flood dan,np:" i~
<br />avoid!'d or signi(ll'antl)' redu~~d. Both Ihe
<br />City Coundl and the Board of Co\mty Com-
<br />mi,"ioner, ha,'e ad"pt('{1 r~solution" a'8"rin<r
<br />iml,lementnlion of 3 .uilable (luotl plai"
<br />mam,gl'menl pr"l{ram.
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<br />FUTURE FLOODS
<br />
<br />100- AND SOO-YEAR FLOODS
<br />
<br />Althoul':h fl(>()(l, with mnp:nitude, and
<br />f...:qu.'n"ic~ '~mibr tothos~ofnoo(hlhat have
<br />,~"urredinthepastcoulrlrecurinthefuture.
<br />di~c"s.ion "f futu,'e fI",l<1s in this nport
<br />r~bte. p..;neipall.,' to lh",e dl'~ij(nated a~ lOO-
<br />and 5llU.year flood:;. A 100-;-par flood has a
<br />peak flow magnitude with a 1 perc~~t chn~~r
<br />of IJein!(" equalled or.'xe..ffied in any given
<br />y.'ar. or a (reC!Ui'ney of occurrence ofnoout
<br />onn'i" 100 ycaro On thi' longlermaverage,
<br />Similarly, a ~I)(}..yea,. flood has a peak flow
<br />m"gn;t~dewlthaO.2p.ercentchanceofl)('in>l'
<br />equalhl or ,'x"~cul'd in lIny given year, or II
<br />fr"'1uen"yofoc<:urr'eneeofaooutoneein500
<br />y.'ar,onthcl"njttermnVera!!e,Sludiesmade
<br />for thi~ rl'p<>rt ,how Ihat"eve,'e floodln"in th.,
<br />studv a,','a e:tn rc~ult fr"m g"t\€ml rain
<br />~('cu'rrin>l' d<lrinj(tlwpl'ri"d (r(lm law "llt"inl(
<br />!(l early fa\!, from sprin!(".early "ummcr
<br />"n(lwml'l\ augmcnkd by ge~,'ral rain, or from
<br />cOllve~tivetypecloudbur,;tstorm,-;in,umm('r.
<br />Specifically, the more :;c'\'en' flm<l, on th~
<br />Ynmpa Hlver \\ould l'eoultfrom widespread
<br />I-!:<'neral rain. The [)lOrt' ,,"w','e fl,,,,,!; On
<br />FOl'tification Cr""k and the dry Itulehesunder
<br />"wily would ,'e,ull from dO\l<11mr,;I"\01""'",
<br />(;"n"ra] rain"wr,m ""mbined with .nnw.
<br />mdt conditions ha"" prwut'ed the maj,,,
<br />flood" "f n",oru in lhp Yamp" Rin'r Ih:;in,
<br />Tl;e~e floo.'h u,ually occur during the period
<br />April through June. A [.(lO-year storm (72-
<br />ho",. dnration) e'luivalentto :l~ percent o( the
<br />probable maximum pr""ipltalion (general
<br />I"ainl for June w,,--;~el\'etcd foru:;ein~omp\lt-
<br />in" th., ;;llO-y"ilr fI,~.d, Pr,,!.lahl.. mnximunl
<br />preeipilatinn amounts \\'~re f<lrni.h~d by th~
<br />H}'dronll'll'(ll'ojo!("icalllmncn oftiw National
<br />Wenth~r Servi'-'e.The frequency of the 5wrrn
<br />srlepte<l w~~ vPrifi<.'d by a 2.I-h"ur point
<br />ra;nfall shldy of th., prpeip;lati"n g">I'p at
<br />Craig. l't'ak flow (or the \1)(J.year floodonth~
<br />Yamr" Riv<'r Wn" read fr"m n flu\\' frdl,,~np..
<br />"urV<' '~'ml'ul".d for R I<"'ati~ll r1nw""trt'''nl
<br />fr"m the point where Forlifieat;on t'rc't'k
<br />
<br />infl,)I\' ent('r. Ih,' ri,'pr, The lOO-year nmd
<br />hydrol(raph Wi<>' palll'rn,'d after lh,' April
<br />1!i7.1 fl""d,'vental Hayden.
<br />
<br />A :l-hour doudbur.l typr thl,nder,torm
<br />was ",k't'ted for compulinll rainfloods on
<br />Fortifical;on Cre"k and the p:ulchc. under
<br />~tudy. The;-,OO-YPardoudbu,..tst"rm"",I,'t'wd
<br />",,,sN\ui\'alrntto4IJpercentofthecloudbur5t
<br />probable maximum precipitation furnished
<br />by the Xalional Wenther Srrvice. A 3-hour
<br />poitltrainfallsturlyofthcprceipilation"alle
<br />,\1 Craig for the period May tl1ro<lgn Hep-
<br />lemher ...'ri(i!'d the frequency of the storm
<br />""ledcd. PrN'ipitation for IhC'lOO-ycarcluuu.
<br />bl'''<\ ,torm was bawd on f;(lperC'entofthr
<br />,>OO.year eloudbur'l storm pfl'cipltalion,Thl'
<br />I'~rc"t\tage u,,<'d W,\" del"rtl1i1wd (rom thl':l-
<br />hourpointralnfall.tudl'.
<br />
<br />l.:nithydrogl"aphsandlll'sralcsforlh.
<br />Yampa !{iver B"sin w,'n' e,timatcd due to
<br />lack of rt'pl""dwible rainn')()tj~ in the "tudy
<br />n....", The unit hydrograph was derived by thp
<br />'~mmationgraph(S'!:raph)mrthod.lltilizinl<
<br />art H-graph uS<ld in a re<.'ent;;ludy of the
<br />Animas River at I.ltlranj(o. A mountain S-
<br />v:ral'htypiealofsmallerd,'ain".o:eba,in.wa"
<br />Ui<'" toprodu<.'e unit hydroJ-(r<\]lhsfor Forti(i-
<br />~ntion Creek and the 1"",,1 drain".o:e ar~a"
<br />"""H\d Crai.o:. Tbis methoonlo.o:y i,;eonsi"tcnt
<br />"'ttn that used for ,imilnr "turlies in the
<br />Steamboat Sprinj(', !{:,n)(<'ly. and Rock
<br />Spring, (Wyom;nl;l nr~ns. A con'ta~t ]058 of
<br />O.15inehc:;perho~r,whichl"cnns;swnlwith
<br />ral<'s",e<l r",. similar studies in IhrHangdy
<br />"",I:;teamooat Sprinj.p;"r~"s, wa,uSt:d on all
<br />an'as within thp .oope of the sl~rJy. Initial
<br />hn,in w,'lt;nKlusw"of().7,~in('he,f"rFortifi-
<br />,-,atio" Creek and "-< much as l,CO ineh~s (or
<br />tht Y:cmp:-t River I)ll"trram from the POinl of
<br />Fortif;cation Creek inllow w~re ~dol'ted, A
<br />jowpri"itiallo.<>.O."Oinl'hi'<.WMIl<"Jforthp
<br />1"",,1 llfl'a' "round C:rai~ bN',"'''e the den~it;'
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