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<br />th~ dr<<i,,,,.,,-,, basin" of the Color<<tlo ...rld
<br />Gunnison Hivers and con'>'ec\ive type doud-
<br />burstsu.rmruno[[fromthedrainal':,'basins
<br />of the trihutary dreams create th(' m<>,t
<br />",\,(".~ flood condition, in the ,tudy afl'a,
<br />rh" unit hydm.,,-raph, for Leach Cr""k,
<br />Horizon Drive Channel, and l....wis Wa,h wen'
<br />develoJ1"dbyusingtheSnyderleehni'lue<<ntl
<br />data!rom scvcrnloimilnrnearbyoo.<;inswith
<br />recorded thu"dersltJrm Tunolf, Rl'!,:i"nal
<br />SMwmelt flood envelope curves for the
<br />Cok.rado and Gunni"." l~i\'er8 Wert' dcw'lo).wd
<br />usin;: flow.dischar.:e frequcncydata
<br />Snowmelt flows of the Colorudoand Gun.
<br />ntson RiW!"8 at Grand Junction were
<br />develof)l"l from frequerlcy curve, for (hu.""
<br />st,,'am, aboV(' Grand Junction, B:I",,..1 on
<br />available data, the 1921 flmd w<<s,ekcwd M
<br />l)('inK moot reprelentative for combin<,d
<br />runoff from thl'two ri"l'rs,and thc,tandard
<br />project flood was determined t<:J hay,' a
<br />fre'1uency of250years(:jO))<'rcentlarl(er than
<br />the 19~1 flood). To e,tabli,h ~tandard project
<br />flow~ on the Col<lrado River. a j,,() )I('rc,'nt
<br />
<br />vllIue of the l~:!l fl,"~Jflows at Pali'ad.' was
<br />del.c'Tnined and then r,'dwcd by H.()I)I) ~ubie
<br />f,~.t 11I'r 'cm",l to refl"ct the eff.."t of
<br />uwtrt.am )'e"""'Olrs For st"ndard proj')('t
<br />fl<l,,"' on th" (;unniwtl Hiv<lr, 1,,0 pl'r"cntof
<br />the lS21 fl,xl<iflov." "t Grand .Junetion ",as
<br />e<(ahli,b,'dandth"ndivinedin\()runoflll.b<WI'
<br />"nd Oclow Blue )Iesa Rese!'\'~;r (5;' and 4".
<br />p"r"ent, r"'llC'divply). BIll<' M,'O<l tk""rvoir
<br />WaH eomp!ded in l\JEjf), Runoff ahove the
<br />rl''''rvoirwascomputedl\.'!aratioofthe19~1
<br />flows and adjusted for pl'esrnt cunditions,
<br />Rc'~('n'oir rcl~a:;"s were made '0 that
<br />downstream channel capacities would notb,'
<br />excc<'ded and as,uminl/," mainwnance of
<br />minimum pow"r pool lev~'l. [)own<tre'lm
<br />runoff was th"n added t<:J "rrive at p...'""nt
<br />"tann:,rd proj''''t flow at Grand Jundion,
<br />~'Iow" in the two ri\'e" we,.e combin""l for
<br />wtal ,tandard proj"d sn~W'melt flows at
<br />n,.a"d .Junction. Tile 11)1)-y('~r flood ewnl ,,"a~
<br />('stablish<"j a~ an ~~ pl,"cent value of tilt'
<br />standard project ev<;nl. The l't',ulting
<br />floodflo,,", """i'hown in Tablc' :l.
<br />
<br />As noted pre"Iou,ly, ,nformatio!loncl"",j.
<br />burst floodin;: in th.e Grand Junction a"ea is
<br />practically nonexistent. Ho\\'r\'cr, rainfall
<br />mea,urement, of 2.;'0 inch,," at Grand June-
<br />tion and ~45 and 2,;'5 inch.e~ at nearby
<br />lo<;atiuns in the n,~i()n h"ve been ""corded
<br />durinll' ~4.h"ur j~,"inds (actual duratioll of
<br />'lor"," unknown), In a 2.ho"r period ;n
<br />an"therlocation,nlllereg;un.2.lf,ineh'-..'s
<br />wl'rt'reeorded Aslandard project storm' for
<br />Learn Creek, Horir.oo Dr;ve Chtl,nnel. and
<br />Lcwis Wash was dpveloped from estimate" Ilf
<br />prr,bahl~ maximum thunder"lorm precipita.
<br />lion ba",d un n'COrded thunderstorms in the
<br />rel':lOn, The standard project storm,
<br />de;;ignated as 10 percent of the :t.hour
<br />probable ma.ximum storm, Wa., ~entercd over
<br />the dra;na~ ba"i"8of lhe three tributary
<br />stre"m", The \l)O'y~a.r and ;,OO'year ,tor","
<br />were developed u"in~ precipitation-fre<luen~y
<br />~u"ve' h",,,,d (ln r,.~ional precipilation daw
<br />r<'cord~d in tbe' we~t,"rn st"teo.
<br />l.os~raw" lorthetributarydrainal':eba.in,
<br />
<br />TABLE 3
<br />
<br />OBSTRUCTIONS
<br />
<br />Peak Flow
<br />",
<br />100-Yaar 500-Y(:8r
<br />Flood Flood
<br />
<br />Natural ob,tructions to floodflo,," inelurlp
<br />t~~'. brush. and other ,,"g,'tation growir.g
<br />~;~n;: ,(",'a,-". Du";ng fhxh. vegetation
<br />impede< floodflow a.1d re~ults In backwater
<br />condition5",ndincre",ed floodheight<. Brush
<br />or tree" wa.<hE:'d outdurinl((Iood,and carried
<br />,jowMtrcamcQuldcoll,>ctonbridgcsorplu.:
<br />culvert..<.thuscreatinl("dammin~effectanr\
<br />0\,,,,'bankflow.A,1l00dflowin,,rea,,,s,masse5
<br />ofdeb,.i~ean dcstroj"a bridge or cause watcr
<br />le"fl" to ris" hil/,"ll('r ""d m"rl' rapidly than
<br />110rl111d, thu~ erodinl( and damaginl(
<br />
<br />PEAKFLQWS
<br />100- AND 500-YEAR FLOODS
<br />
<br />Stream
<br />
<br />(,,,l,,r,ld,, Riv,'r
<br />
<br />Location
<br />Abow ",,,uth ofr_;unnl>.{m ltj",",-
<br />Helnw mOLLthof (;lllU"S"" Ili",'r
<br />
<br />C"lor",rloR;vpr
<br />
<br />C;,,,,,.i'u,,r:ih'
<br />
<br />,\i n"d,..,d ,lutLcti"o
<br />
<br />r"a....hCr"""
<br />11",'i"""Pri""
<br />Channel
<br />l"w;,lI'a,"
<br />
<br />At II Road
<br />
<br />;_;;l,\~~i ~~.'I\J(J
<br />t\2.<I\/ii lo7/~)[)
<br />2il.ono 2,;.OO()
<br />l.~\~i 1,211r1
<br />1;(~\ 1.~IHi
<br />1,11)0 :J,Nill
<br />
<br />At I'Hll"lwn,kn,'..e nanchnwns I)i\<'h
<br />
<br />At 1.7i..'
<br />
<br />were ",timawd d\l~ tH limiwd streamflow
<br />data with Which to repruduee doudbur8t
<br />floods. I-Iydrolol(ists familiar with th~ area
<br />e,tablished],,"""atl!.,r,,,.<edonpreeipitation
<br />datafurGrand.lllnd;Ol\andi>r"e;~ilationand
<br />streamflow dal", [or similar ba"ins in other
<br />parts of the r)'l':ion, with consirleration l(;ven
<br />to topllgraphy.,'el-:eUltion,and ""ileondition,.
<br />1"'"Hrate,adopt",,1 for the lOO-and;,O()-year
<br />cloudburst !I{)()(b w"re o.n inch initial loss
<br />",nd 0.20 inch l*r hour C<Jn"tant looso" the
<br />tributary otrearns, The ,'r<ulting flow8 are
<br />containe,] in T",ble:l_
<br />[nformati()nonlO-and50-y,'arfloodevents
<br />was also d,'v€lopl,d ao p"nof the h;'drolOj(ic
<br />~tudie<;co"ducted forthi,report. These would
<br />ba~ically he snowmelt floods on the Colorado
<br />and Gunni'lOn Rivers and ctoudbur,;t flood~on
<br />lh,'tributarystrellll\s. but, with lhecx"eption
<br />of showin;: their water surface profile5 on
<br />Plates 1;8.74, an' (lot further eovered it> the
<br />n'p<>rt.
<br />
<br />ablltment,. approach,,,. and tht' "\'~rlyin"
<br />Nadbed.
<br />Tn g~nc~a!, obs:ru~tiQr." )'''st~icl floe-dr.o",,,
<br />and maycauseoverbankflow<.unjlredictable
<br />areas of flo"dios:. J>C<l~ib]e damaK€ to Or
<br />destruction of brid!,:~, and other <tream
<br />cro~sinl':o, and incl'l'aseQ velocity of Dow
<br />imm,'diatdy dowll5trr",n. ;..I,,,,t ol...he otr"am
<br />CT'-"'SinK" in the "llldy area ~re ob,t,""clive to
<br />no"rlflow,. P~l"tinent data on all slructuNs
<br />art' ,bow" in Tn!>l" ,1. Th,.df".et olol1:<lr""-
<br />tinn.< m"y 1", ",'pn on Piau'" ;;'<~-74,
<br />
<br />. Thc' """OJ "O;~I:;"" ~",,,,.... :Ih" ""',' .,,,,,,, c~,,,b;r,,.,i,,,, ,~ ,r.,"""",I,,~i,'~1 ,,,",,,U,,,,,. lh", ",,' '''''',_..,1''''',..-1,""",,,,,1,1, ,,;'."",'l.''''l''.....! ...h.' -",,,~,",,,hi.,.\ ","'''..n "ilich.' "r,''''" 1_''''';1> L, '"".,c",
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