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<br />n[>eded du,'in>: the summer and fall.
<br />However, rapid mdtinll of mountain mow.
<br />packs in s!lrin~ and earlj' <"mmcr j, the
<br />majorca."eoffloodinp;in the Htudyareaalonl!"
<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"u(lbnrst storms'
<br />
<br />TABLE 2
<br />
<br />DRAINAGE AREAS AND
<br />HEADWATER ELEVATIONS
<br />
<br /> Approxlm8t8
<br /> Approxlmale Elevallonol
<br />Location DralnageAree HeadwalerAre8
<br /> sq. ml. ft.(mal)
<br />Ga\[inl( Station 17.1O(l 12,000
<br />n"arf'ruita
<br />Gal(inlo;Station 1,9:10 14,(l()0
<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 />5fream
<br />
<br />Colonulo River
<br />
<br />(;unniwn River
<br />
<br />IJ,ach Cn",k
<br />Hori;.on Drive
<br />Channel
<br />IRwi,W"8h
<br />
<br />Theclirnaw of th" ar<'a is arid to semiarid
<br />with y,'arly pr,'cipit;ltion 'l.Vcraginj.(about8
<br />illch... at Grand Junctioll. [romaoout 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 l'r<'eip:tation in the hi~her
<br />elevations oceurs..., snow and a deep 'now.
<br />packaecumulaw8. Temperatut'<';lare oflcnin
<br />tbenindil'Sin thusummer and b<:lowfreezinlj"
<br />in the winl€r, (k('a~ional1y. 8ummHtime
<br />kmpel"ature Illay exeeed 1000 and winter
<br />
<br />NATURE OF FLOOD PROBLEMS
<br />A~ now!. most or the annllal pr<'Cipitation
<br />in the hi,,;hn "'"ion<ofthe basins of tht'
<br />C"loradn and Gunni""n Riversoccu"a88now
<br />and a d.",1' "nowpaek aceumul.~te". i;,'ncr"l
<br />.."i"'tor'1" coverin~ lar"e al"<~a< for eXl<'nded
<br />
<br />Dale
<br />
<br />Odober18,1908
<br />AUl!"ll~t 24.1921
<br />St>plcmlx'r22.1941
<br />
<br />Analysisof,,,,ailabledataindicatesthatthe
<br />100.year flood on the ColoranoandGllnnison
<br />Rive,'s wouln re"lllt from "nowmelt runoff.
<br />and th"tthe ;>OO-year flood would becau,;,,,]
<br />
<br />lemperaturemaydrol'aslowa".20'.:\"aturli.l
<br />ve"etation in valley ~reas primarily con"ists
<br />ofcotlonwood and willow, d,,,..rtshrub, and
<br />an understor)' of hardy I'("ra""s. Prominent
<br />1~lwet'n5000and800(lf,~tarejuniper,pi1'",n
<br />pine. oak, bi>: sagebrush, and Dou>:I..., Fir,
<br />!,'rom 8()00 fed lo timb€rlin,'. wj.(etation
<br />eon,ists mainly of aspen. spruce, ~ub'alpine
<br />rir.lod~polepine."'ndnatl,'e!l'rasl\€sand
<br />shrubs. VCl'("etationissparscabovetimbcrline
<br />but inelude" 11;,....%'.', ".d!,:"'3, and alpill~
<br />willow.
<br />
<br />FLOOD HISTORY
<br />
<br />Stream" in the ;twi,\' area. e<n.'d"Uv the
<br />CAlorado River. have a Ion\[ hist"ry of
<br />l100dinJ>;.blltdefinitivedataonfl(l.udsare
<br />unavailable. Th~ flood;n!,:of June-July 1~4.
<br />the earliest o{ rccnnl in the 8t<ldy an'", is
<br />lI;ener&lly considered the mm;t ",'Vere known
<br />in (;rand Junction. It re';lllk~l from rapid
<br />meltin;!: of a d,'ep ~nowp""k ""d ron"urr<,nt
<br />
<br />Iwr;,"lsean occur intlwre"iondurinlf<prin!l
<br />and summer. C"nwrtiw' tnw clnudbu",t
<br />,torm, of ~mall ar.'al <>xlPnl, which ""count
<br />for .~bout h",l[ofthenormal anmlal pr<'Cipiu..
<br />tion in the Grand ./\Jnetinn area, ,,,,n ut
<br />
<br />creal.,,, tMe hij.(hesl flo<Jdflows on the
<br />tributaries originating in the Book Cliff,ar,'a.
<br />While therc is little definitive information
<br />available on cloudburst Iloodil\j.(on the""
<br />triuutarie~. preeipitaliun station~ in th<>
<br />(Orand Junction area ha\le rpenr,l,'d the
<br />followini>: I-day rainfall amOllnt" (actu"l
<br /><tormdurationH unknown):
<br />
<br />Amount
<br />(Inch"$)
<br />
<br />2.50
<br />
<br />1.59
<br />un
<br />
<br />by snowmelt aUjl'lnented bv rain.Thc 100. and
<br />,;oo'y"",r floods on the trihutary stream"
<br />would rl'Sull from cloudburst storm~
<br />
<br />h,',,"vy r,,;n,. ()th,>c fl(~",. nn th,_' C.(>lo~"da
<br />Rive,' were r"eonl,'din 1911,1>1:<0, 1921.1935,
<br />1952, and 1%7. On the nunn;"", Ri.'er,
<br />f1oodin" look piaL'" in 1!120, 1921. and 1957.
<br />The floodflow uf May lfr20 was the larj.(~"t
<br />recorded on th,' Gunni&>n Ri.'er. !\ewspap('r
<br />accounts'describc lhe 19S7 fl()<)da^ follows:
<br />
<br />':-;,,,,,,,11",'0..(',,1,,,,,,10,,,,,1,;,,,,,,;,,,,, K;w,,'lo"""'XI"'C"'"""","('"r''e"''''''''',n('Il'''"0~1'''''
<br />, S',"olbo,'"". fi",Ii,,~,," "II :It., ,",\'ut"""'l'N,b.ldy ~'''ul~ "," '''',,''' <\,," to trIO' ,,,,all ~......' ""ent 01 ,'""dh",,,,
<br />""'''"''.
<br />
<br />, ~:"",]"""I ~r"''' "';<"0~;: '" "'p;'"
<br />
<br />.,
<br />
<br />.
<br />,
<br />
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