<br />
<br />Th~ most r~c"nt nand in th" Craijt an'"
<br />occurred alunlt" tn,' Yarl1~a Rin'r in April
<br />197,1. Rapid <nowmell.o:en~r;'ted by unseawn-
<br />ably warm w"ath~r wa~iLuj.(ment~d by rain on
<br />are"~notco\'eredbysnow!)('t\\"ecnSte"mb(mt
<br />"prlt\;:~ and Craij.(. Thert' wa<, how",",'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 critie~1
<br />;itu~tinn \\'a< at lllc mllnlnpa\ water IJ\anl,
<br />whkh was s"r.-ounrled by f1oodwatc'r. hut
<br />protettcd b)' ha>til,. bui\t rlikt" Railroad
<br />se,.\'iN' 10 Crail; \\"a.cut off (or morc than l\
<br />week by badly dllmaged t,.ack in se'.eral
<br />lo<:ati~ns ktwel'n Crail;an<ll'hippsburl;.
<br />
<br />~.,~."" t 1, Y.mJ'" Riw, t:.."In"w<""'rt,wo""rIYQICr~'~, Aprii~J.:ll, 1974.ll'how~c.rm'!Q' mo...io<",",,,,",).o!'o,' Muff.!
<br />C"llO\)" l'lannin~ Departme",.1
<br />
<br />FLOOD DAMAGE PREVENTION
<br />
<br />Followi"...- lIw 19,17 n'~1<1 i" emilo[, Vo,.lifi.
<br />cHttOn C,vek "'I'" im!Jrov<'d 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 />e\ltt;nJ.( a now. str:lil'htchan"d ," thr lowf'r
<br />,.,'aoll ~(Ihr ~r('"k: "trnil'htl'ninganrl impro".
<br />inglh,' creek upstream fl"Om Illene", chan"~]
<br />oection: and pro'.'di"l( Il>w, 3poiltYlle I",""-'s,
<br />Thi, work, plus 3ub.tantin\ n"t~rn] chan"d
<br />i'nprov"mcnt,bJ('tl>incrc'asedf\o"'wlociti~s.
<br />has mnl<.'!'ially ,l<""rt'a~t'd i"~ jam I'robl<'rm.
<br />kfjHn1sthat h'\\"~(Jo:"urt.ed in rN'entyea,."at
<br />'I <'<'W"'. liltt',.ro,,,in,,u[l,tr,'nmfrom lliyhway
<br />.IO"nuatth,',.ailroaucr",;sinj(dowMt,.eam
<br />from thehij(hw,,"yhHveheen remo..~d by city
<br />ami railro"d mainlenmw" c...."'s. A"ide from
<br />thc .'merg~""y work d"Sl'rllK',1. which wa,!
<br />'''-''''I'k-ll,l ,n l~qll. thrre are no fo,.malized
<br />fl,,,,,ll"ontrol projd'l.<hnvinl(andfi'tl in th.,
<br />
<br />,tud) ar~,,- CUJrlI'J'ehens;wl-'lanseumpri,inl'(
<br />a 6IJ,OIIO aere.fOOI floodeont'Xll "'''''1"\'Oirllr
<br />Ie,",,,, eon'trL"'ti",,, ("nantlel impro\"{'mt,,,t
<br />\\"ork. and ""placellwntofobstructivebri<l)l6
<br />have bt'Cn ~tlldi<'d a'''! I'm[wl<.'rl hut never.
<br />authori,,'d,
<br />The Cily of L'l"aij( and Molfnl Counl'. "I"..
<br />eligible for flood in'lll.l'-'Lt'e und'~r tn.. ~mer.
<br />I'eney ph""" o( th~ Xation,,1 Flood In,~rance
<br />ho.o:ram, To ma;ntai~ e1il'ibiJlty. th~ pru.
<br />I(,.,,-,n r~'lllirl'" 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 dnn,np:" i~
<br />avoid!'d 01" signi(ll'antl). redu~~d. Both Ihe
<br />City Coundl and the Board of Co\mty Com-
<br />mi,"ionel"' ha,.e adopt,,,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 />A\thOlll':n fl(>()(\, with mnp:nitude, and
<br />f...:qu.'n"ic~ '~mibr I.othos~ofnoo(hlhat have
<br />,~"urredinthepastcoulrlrecurinthefuture.
<br />di~c"s.ion "f futu,.e fI",l<1s in this nport
<br />r~bte. p..;neil-'all.,. to th",e dl'~ij(nated a~ lOO-
<br />and 5l)U.year flood:;. A 100-)""ar flood has a
<br />peak flow magnitude with a 1 perc~~t chn~~e
<br />of IJein!(" equalled or,'xe,'<:.'<Ied in any given
<br />y,'ar.nra (reC!Ueneyof occurrence ofnoout
<br />o,,",'in 100 ycaro On thi' longlermaverage,
<br />Similarly, a ~I)(}-.yea,. flood has a peak flow
<br />m"gn;t~dewlthaO.2p'ereentchanceofl)('in;.:-
<br />equa\hl or ,'x"~cul'd in any given year, or II
<br />fr"'1uen"yofoc<:urr.enecofaooutoneein500
<br />y.'ar,onthcl"njttermnvera!!e,Sludiesmade
<br />for thi~ rl'p<>rt ,how Ihnt"eve,.e fluodln"in th.,
<br />stud\" a,.,'a c:tn rc~ult fr"m g,'neml rain
<br />~"cu'rrin;.:- d<lrinj(tlw[Jl'ri"d (r(lm law "llt"inl(
<br />10 early fa\!, from sprin!(".early "ummel'
<br />"nowml'l\ augmenkd by ;.:-e~,'ral rain, or from
<br />COllvective type cloudbur,tstorm.,i",umm('r.
<br />Specifically, the more :;c"'en' flm<l, onth~
<br />Ynmpa Hlver "ould l.eoultfrom widespread
<br />i':,'neral rain. The [)lon' "",,,',.e fl,,,,,], On
<br />FOl'tification Cre<<k and the dry Itulehesunder
<br />"wily would ,.e,ull from dO\l<11mr.;I"lor",",
<br />(;"n"ra] rain"wr,m ('ombined with sn"w.
<br />mdt c"nditions ha"" produt'eu the maj,,,
<br />flood" "f n",oru in lhp Yamp" Rin'r Ih:;in,
<br />The,,, floo.'hu,uallyoccurdurlng the period
<br />April through June. A [.(lO-year storm (72-
<br />ho",. dnratio,,) e'luivalentto :l~ percent o( the
<br />prDbablc maximum pr""ipltalion (general
<br />I"ainl for June WlB ~e\\'etcd for use in ~ompllt-
<br />in" th., ;,llO.y,'ar fI,~.d, !'r,,!.lahl.. mnximunl
<br />preeipilatinn amounts were f<lrni.hcd by th~
<br />H}.dronH'll'",.ojo!("ic"lllmn"h oftiw Nntinnal
<br />Wenth~r Servi<.'e.Thc frequency of the 5wrrn
<br />srlepte<l w~~ vPrifi'.'d by a 2.I-hl>ur point
<br />ra;nfall shldy of th., prpeip;lati"n g";.:-e at
<br />Craig. l't'~k flow (or Ihe !1)(J.ypar flood on th~
<br />Yampa Riv"r \\'~" read fr"m n flo,," frdl,,~np..
<br />curV<' '~'ml'ul<"(1 for H I,lt'ati~ll dnw""trt'''nl
<br />frnm lhe point where Forlification l"rc,<,k
<br />
<br />infl,)I\' enl('r_ Ih,' ri,.pr, The lOO-year nmd
<br />hydrol(raph w", panl'rn~'d after lh,' April
<br />1!i7.1 fl""d,'vental Haydcn.
<br />
<br />A :l-hour doudbur.l typr th\,nder,torm
<br />was ",k",ted for compulin.o: rainfloods on
<br />Fortifical;on Cre"k and the p:ulch~s under
<br />~tudy. The ;',OI)-yeardoudl)U,.~tstnrm ",,\''''wd
<br />",a""qui,.alrntto4IJpercenl.olthecloudbur5t
<br />probable maximum precipitation furnished
<br />by the Xalional Wentner Srrvi~e. A 3-hour
<br />point rainfall sturly of th~ prccipilation "a.o:e
<br />,\1 Craig for the period May thro<lgh Hep-
<br />lemher ...'ri(i!'d the frequency of the storm
<br />",,\e<'lcd.l'rN'ipitationforlhC'lOO-ycarcluuu.
<br />b\lr<l ,tnrm was bawd on f;() per~entofthr
<br />,>O(l.)"ear ~loudbur,1 storm pfl'~ipltali()n, Th~
<br />pcrc,'ntage u,,<'d w<\,del"rtl1irwd (rom thl':l-
<br />hourpointrulnfall_tudl'.
<br />
<br />l.:nit hj"dr"gl"aph~ and Ill'S rates for Ih.
<br />Yampa !{iver B"sin ",,'n' e,timatcd due to
<br />I~ck of fl'pl""dwible rainn')()tj~ in the "Iudy
<br />nN'a, The unit hydrograph wa~deriveu byth"
<br />'~mmationgraph(S'!:raph)mrthod.lltilizinl<
<br />art H-graph Ilsed in a re<.'ent;;ludy of the
<br />Anim~s River at I.lllranj(o. A mountain S-
<br />Yl'al'hlypiealofsmallerd,.aina.o:eba,in.wa"
<br />Ui<ed to produce unit hydroJ.(r<\jlh~ lor Forti!i-
<br />~ntion Cr""k and th" 1000al draina.o:c ar~a"
<br />"""H\d Crail<. Tbis melhoo,,]oI<Y i"eonsi"t~nt
<br />Wtth that us<'d for ,imilnr "turlies in the
<br />Steamboat Sprinj(', !{:,n)(<'ly. and Rock
<br />Spring, (Wyom;nl;) nr~ns. A con'ta~t ]058 of
<br />(l.15ineh":;perh"~r,whichl,,cun";swnlwith
<br />ral<'s",e<l r",. similar studies in lheHangdy
<br />"",l:;teamooat Sprinj.p;ar~"s, wa,u",don 1I11
<br />an'as within tn~ .oope of the sl~rJy. Initial
<br />hn,in w,'1I.;nKlusw"of(l.7,~in('he,f"rForl.ifi.
<br />eati"" Creek nnd as much as l,CO ineh~s (or
<br />tht Y:<mp:-t Rivcr I)ll"l.rram fr"m the pOinl of
<br />Fortif;cation t'rcl'k inllow w~r~ ~dol'tcd, A
<br />joweri"itinllo.><.O."Olnl'ni'<.wMIl<"dforthe
<br />\,,,.,,1 afl'a' around C:rai~ bN""'''e thc uen~it;'
<br />
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