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<br />th~ dr<<i,,,,.,,-,, basin" of the Color<<uo ..nd
<br />Gunnison Hiver, and con'>'ec\ive type doud-
<br />burstsu>rmruno[[fromthedrainal':,'basins
<br />of the trihutary dreams create th(' m<>,t
<br />,,'\',"'~ flood conditio"s in the ,tudy afl'a,
<br />Th" unit hydm.,,-raph, for Leach Cr""k,
<br />Horizon Drive Channel, and l....wis Wa,h wen'
<br />develo)WdbyusingtheSnyderleehni'lueanu
<br />data!rom scvcrnloimilnrnearbyoo.,inswith
<br />recorded thundersltJrm runoff, Rl'!,:i"nal
<br />SMwmelt flood envelope curves for the
<br />Col'-'rado "nd Gunni",,, f~i\'er8 Wert' dC"l'lo))<'d
<br />usin;: fl()w.dischar.:e frequeneydata
<br />Snnwmelt flows of the Colorudoand Gun-
<br />ntson Rive!"8 at Grand Junction were
<br />deveiop"d from frequency curve< for (hu.""
<br />st,,'am, aboV(' Grand Junction, B:l",,.-I ()n
<br />availahledata, the \921 flmd w<<ssekcwd M
<br />l)('inK moot reprelentative for comhin<'d
<br />runoff from the two ri"ers,and the,tandard
<br />project flood was determined t<:J hay,' a
<br />fre'1ueney of250years(:jO))<'rcentlarl(er than
<br />the 19~1 flood). To e,tabli<h ~tand"rd pr<>jeel
<br />flow~ on the Col<lrad<> River. a j,,() 1I('rC,'nt
<br />
<br />vlllue of the l~:!l fl,"~Jflows at Pali'ad.' was
<br />detc'Tninrd and then r,'dwcd by H.()I)I) ~ubi~
<br />f,~.t 11I'r 'cm",l t<> refl"ct the eff.."t of
<br />uwtrt'am )'e"""'o'rs For standard proj')('t
<br />fl<lw, on the (;unniwtl Hiv<lr, 1,,0 ))<'r"~ntof
<br />the lS2t fl<xl<iflov.-- at Grand .Junction ",as
<br />e<(ahli,h,'dandth"ndivir!€din\()runoffll.l)<JV\'
<br />and Oclow Blue )Iesa Rese!'\'~;r (5;; and 4.-,
<br />p"r"ent, r"'pc'div"ly). BIll<' M,''''' IW"'-'r..oir
<br />WaH eomp!dcd in l\JEjf" Runoff ahove thr
<br />rl''''rvoirwascomputedl\.'!aratiOQfthrI9~1
<br />flow" and adju,ted for pl'r"€nt conditions,
<br />Rc'~('n'oir rcl~,,""s wrrc "'ad~ '0 that
<br />downstream channel capadtie" would not!.:"
<br />cxcc<'ded ~nd as,uminl/,' mainwnanee of
<br />minimum pow<,r pool lev~'l. [)()wnstre'lm
<br />runoff was th"n added t<:J arriv" at p...'""nt
<br />"tann:,rd proj~d flow at Grand Jundion,
<br />~'fow" in the two ri\'er, were combine<l for
<br />wtal <tandard proj"d ,nowmelt llowo at
<br />nrat\d .Junction. The 11)1)-y('~r flood evt'nl wa~
<br />"stalJlish.."j a~ an ~\J ))<,rcent value of th('
<br />standard project eV<;lll. The l't'<ulting
<br />{Ioonflow, """i'hown in Tabl.., :l.
<br />
<br />As noted pre"Iou,I,-, ,nformatiolloncl"",j-
<br />burst floodinl( in the Gralld Junction a"ea is
<br />practically nonexistent. Hov.'r\'cr, rainfall
<br />mea<urements of 2.50 inche" at Grand Jut\c-
<br />tion and ~45 and 2,;'5 inches at nearby
<br />location, in th" ,',,;:ionhave been """"rded
<br />durinl<" ~4,h"ur l~..rinds (actual duration of
<br />slorm" unknown), In a 2-hour period ;n
<br />an"ther location In llle region. ~.\f, inch...,
<br />""'rt'reeorded A stannard project stllrm' for
<br />Leach Creek, Horir.on Dr;ve Chtl,nnel. and
<br />Lewis Wash was developed from estimate" ()f
<br />prr,bahle maximum thunder"tol'm precipita-
<br />tion based on r<.'C<Jrded thund"rstorm" in the
<br />rel':lOn, The standard projeet storm,
<br />de;;ignated as 10 percent of the :t"hour
<br />probablo ma.ximum storm, Wa., ~entered over
<br />tbe dra;na~ basi"s of the three tributary
<br />stream", The !l)O-yea.r and 5()()'year <torm"
<br />w"redeveloped usin~precipitation-fre<luenty
<br />cu"'"c' b"--,,,d nn r,.~ional prccipitatwn daw
<br />r"cord~d in tbl' we~t,"rn state,.
<br />LossraW"forthetributarydrainal':ebai'in,
<br />
<br />TABLE 3
<br />
<br />OBSTRUCTIONS
<br />
<br />Peak Flow
<br />01,
<br />100-Ya8r 50e,Ycar
<br />Flood Flood
<br />
<br />Natural ob,truction, to f!oodflow inclunp
<br />t~~'. brush. and oth~r "f'gt'tation growir.g
<br />~;~ng ,(",'a,-", Du";ng floods, vegetation
<br />impede< lloodflow a.1d re~ults in backwater
<br />conditionsandincrc",ed flood height,. Brush
<br />or tree" "'lL<hEXI outdurinl(flood,and carried
<br />,jowMtrcameouldcoll,>tOtonbridgcsorplul(
<br />culvert.<.thuscreatinll:"dammin~dfcctanr\
<br />o\,,,,'bank flow.A,llO<Jdflow in"rea<"s, masses
<br />of debris can d<.'Strora bridge or cause wawr
<br />lewl"wris" hil/,'ll('r""d m"..' rapidly tl1"n
<br />11ornu<l, thu~ erodinl( and damaging
<br />
<br />PEAKFLQWS
<br />10e, AND 500,YEAR FLOODS
<br />
<br />Stream
<br />
<br />('"Ior<'r!" Riv,'r
<br />
<br />Location
<br />Abow m"ut-h oft-_;unn',,<m ltj",",-
<br />lIel"w mOLLthof (;lllu,i"", !\i",'r
<br />
<br />C"loranoR;\"pr
<br />
<br />c;,,,,,.iSu,,r:;h'
<br />
<br />,\i nr.>,-,d ,Iu"cli""
<br />
<br />r;,~...h Cr,"'"
<br />11.."'i",,,,!)ri\'('
<br />ehannol
<br />I"wi, Wa,"
<br />
<br />At fl Road
<br />
<br />;_;;l,\H~' ~~.,)(J(J
<br />t\2.<~'O \07.t'H)(1
<br />2il.OHO 2.i.OO()
<br />l.~\~' 1,21111
<br />1;(~\ 1.~IHi
<br />\,11)0 :J,N'II
<br />
<br />At Illdqwn,kn,',e Ibnchnwns I)i(,'h
<br />
<br />At 1,7i,'
<br />
<br />were ,,<timawd d\l~ t" limiwd strcamflow
<br />dat" with which to rcpruduce doudbur8t
<br />floods. Hydrolol(i"t, familiar with the arca
<br />e,tablished I,,"" ,'atl!S r""edun precipitation
<br />d"tafurGrand.lllnd;Ol\andl>r~c;~ilationand
<br />~treaml1ow dal.a for similar b,,"ins in oth~r
<br />parts of the ""I':ion, with consideration !(;ven
<br />to topography. ,'e;:eUltion, and soil eondition<.
<br />t..,""rate<adopted for the 100-and;,O()-y""r
<br />c1oud!.:urst !IO()(b w<,re o.n inch initial loss
<br />and 0.20 inch 1'><'1' hour C<Jn"tant logs on the
<br />tributary ,treams, The ,'r<ulting flow" are
<br />contained in Table:l_
<br />[nformati()nonlO-and50-y,'arfloodevcnts
<br />was also d,'vdopcd a, pan of the h:,drolOl!:ic
<br />~tudie,co"ducted forthi,report. Th",,,wo,,ld
<br />ba~ically he snowmelt floods on the Colorado
<br />iind Gunni'lOn River, and cloudbur,;t flr>llt-j~on
<br />th,'tributarystrr.lll\s. but, with thecx"eption
<br />of "howinl( their water surface profiles on
<br />Pla.tes 1;8-74, an' not further "overed in the
<br />r,'port.
<br />
<br />ab(ltrnent,. approach,,,. and tht' "\'~rlyin"
<br />r<>adbed.
<br />[n g~ne~a!. ()bs:ru~tions ""st~ict flocdr.o"",,
<br />and mayeauseoverhankflow<.unl"edictable
<br />arca, of noodins:. p",dble <lama"c to Or
<br />destruction of brid!,:~< and other stream
<br />cro~sinl':s, and incrl'a>;,Jrl vdocity of Dow
<br />imm,'diiitdy dowm,trrafl\. C\ol'>st of t.he ,tream
<br />aossinK" in th""tudyarea~reob,t,",,cti"eto
<br />floonflow<, P~rtinent data on all slructuNs
<br />art' ,hnwn in Tn!>l" ,1. Th,' !'ff.,,,t ofob:<trlJ"-
<br />tinn.< m"y 1", ~('pn on I'la.tl", ;;'<~-74,
<br />
<br />'Thc' """OJ "O;~I,;"... ~","", ,Il<' ""',' .,,,,,,, C~I"b;,.".,i,,,, ,~ ,r.,"""",I,,~i,'~1 ,<""Un"'. lh", M,' ""',..,I",,,'d
<br />""",,,,,I.i, ,'i'."",'l.''''l<<'...! ,,0.' _""~,',,,hi,',\ "t"" ,n "ilich.' ",.""," 1_''''';1> "',,,,,'c',i
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