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<br />n[lCded du,'in>: the summer and fall.
<br />However, rapid mdtinll of mountain mow-
<br />packs in s!lrin~ and earlj' <"mmcr i, the
<br />majorca."eoffloodinp;in the Htudyareaalool!"
<br />the Colon"lo "nd{;unni",m Riv"rs' Flood,n)(
<br />i, mo"t sev"r<' when snowmelt is aUJ;m"nted
<br />by rain.
<br />Intense rainfall fr"m cl"urlbnrst storms'
<br />
<br />TABLE 2
<br />
<br />DRAINAGE AREAS AND
<br />HEADWATER ELEVATIONS
<br />
<br /> Approxlm8t8
<br /> Approximate Elevallenol
<br />Location Drainage Area HeadwalerAre8
<br /> sq. ml. ft.(mal)
<br />Ga\[inj.( Station 17.1O(l 12,000
<br />n"arf'ruita
<br />Gaj.(inlo;Station 1,9:10 14,(l1l0
<br />near Grand Junction
<br />At m<>uth 25 5,500
<br />At"F" Road 2 5.r.oo
<br />At mouU> 5 5.500
<br />
<br />Stream
<br />
<br />Colonulo River
<br />
<br />(;unniwn River
<br />
<br />IJ,ach Cn",k
<br />Hori;.on Drive
<br />Channel
<br />l",wi,W",h
<br />
<br />Theclirnaw of th" ar.'a is arid to semiarid
<br />with y,'arly pr,'cipit;ltion 'l.Vcraginl(about8
<br />illch... at Grand Junctioll. rromaoout 10 to 15
<br />inch.., in headwalcr areas ofU>e Book Cliffs,
<br />andaboul40 in€hesin the headwater rel'\"ions
<br />of the Colorado ann (:unnison Rivers. ~lostof
<br />lh~ annual pr<'eip:tation in the hi>:her
<br />~levations occurs..., snow and a deep '''ow'
<br />packaecumulaws. Temperatut'<';larc oflcnin
<br />tbenindil'Sin tbusummer and b<:lowfreezinlj"
<br />in the winter, (k('a~ional1y. summHtime
<br />kmpel"atur~ Illay exeeed 1000 and winter
<br />
<br />NATURE OF FLOOD PROBLEMS
<br />A~ !lOW!. most or the annllal pr<'Cipitation
<br />in the hi,,;hn r<'.o:ionsofthe basin' of the
<br />C"loradn and Gunni,u)n Ri\'frsoccu"a"now
<br />amI a d,',,1' "nowpack :l.ccumul.~te", i;.'ncr"l
<br />.."in;;tor'1" coverin~ lar.o:e al"<~as (or eXl<'nded
<br />
<br />Dale
<br />
<br />Odober18,1908
<br />AUl!"u~t 24.1921
<br />Stoplcmlx'r22.1941
<br />
<br />Analysisof,,,,ailabledataindicatesthatthe
<br />IOO-year flood on the ColoranoandGunnison
<br />Rive,', wouln re"lllt from snowmelt runoff,
<br />and th"tthe ,>OO-year flood would becau,;.,,]
<br />
<br />lemperaturemaydrol'aslowa,,-20'.:\"atorli.l
<br />vu"etation in valley ~rea.' pr;marily con"ist,
<br />of cottonwood and willow, dt'>lertshrub, and
<br />an understor)' of hardy 1'\"r<\SS(,s, Prominent
<br />1~twet'n5000and800(l1(~tarejuniper,pi1'",n
<br />pine. oli.k, bi>: sagebrush, and n"u>:Ia._ Fir,
<br />!,'rom 8()00 fed to timberlin<'. wl{etation
<br />eon,ists mainly of a'pen. spruce, ~ub-alpine
<br />rir.lnd~polepine."'ndnatl,'e!l'ra,l\€sand
<br />,hrubs, VCl'\"etatienissparscabovetimbcrline
<br />but inelud.." 11;,....%'.', ".dll;"'3, and alpin"
<br />willow.
<br />
<br />FLOOD HISTORY
<br />
<br />Stream" in the ;twi.\' area. e<n.'d"llv the
<br />CAlorado River. have a Ion\[ hist"ry of
<br />l100dinJ>;,blltdefinitivedataonflo,udsare
<br />unavailable.Thrfloodinll;oIJune-Julyl~4,
<br />the earliest of rce"nl ;n the st<ldy an'", is
<br />lI;ener&lIy considered the mm;t "<'vere known
<br />ill (;rand JUllction, 1t re,ulk~l from rapid
<br />meltin;!: "Ia d<'rp ~nowp""k ""d e",,<curr..nt
<br />
<br />p..rj,"lsean occur intlwrc"ionrlurinlf<prinll
<br />and summer, Conwetiv(' tnweloudbu",t
<br />,torm, of small &r<'al<,xlPnt, which "<",,eunt
<br />for .~bout h"lfofthenormal anmlal pr<'Cipiu..
<br />tion in the Grand ./\Jnetinn area, ,,,,n bt
<br />
<br />creat.,,, the hil(he'l fl""dflows on the
<br />tributarie,originatingin the Book Cliffsar<'a,
<br />While therc is little definitive information
<br />available on cloudburst floodinl(on the><<e
<br />tributarie~. preeipilalion station" in thf
<br />(Orand Junetinn Ilrra have rpe"r,l,'d the
<br />foll"w;nl1: I-day rainfall amollnt" (adu"l
<br />,tormdurationH unknown):
<br />
<br />Ameunt
<br />(Inches)
<br />
<br />2,50
<br />
<br />1.59
<br />un
<br />
<br />by snowmelt aUjl'lnented bv rain. The 100. and
<br />:;QO-y"ar floods on the trihutary stre&m"
<br />would rl'Sull from cloudbur5t storm~
<br />
<br />h.>avy rain" Oth,>c fI,~><1. "n th,_' C.(>lo~"da
<br />Rive,' were r"eonl,'din 1911,1>l:<O, 1921.1935,
<br />1952, and 1%7. On the nunni"", Ri.'er,
<br />f1ondin.o: look pia..., in 1!120, 1921. and 1957.
<br />The floodflow uf May lfr20 was the larl{""t
<br />reeorded on th,' Gunni&>n Ri.'er. !\eWSpal'Cr
<br />aecuunts'deRcribc lhe 19S7 flooda^ follows:
<br />
<br />':>,,,,,,,11",'0.,(',,1,,,,,,10,,,,,1.:,,,,,,;,,,,, K;w,,'lo"""'XI"'C"'""''''0(''''''e"''''''''',n('Il'''"0~1'''''
<br />, S',"olbo,'"". fi",Ii,,~,," "II :h., ,",j,u\;"''''l'N,b.ldy ~'''ul~ "," '''','''' <\,," to trIO' ,,,,all ~",,,' ,'x'ent 01 ,'",,,dl,,,,,,,
<br />""'",",
<br />
<br />, ~:"",]"""l ~r"'" "';<"0~;: '" "'p;'"
<br />
<br />'<
<br />
<br />,
<br />.
<br />
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