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<br />
<br />As noted previously, informalion on doud-
<br />burst flooding in the Grand Junction area is
<br />practically nonexistent. However, rainfall
<br />measurements of 2.50 inches at Grand Junc'
<br />tion and 2.4.'; and 2.55 inches at nearby
<br />locations in the region have been recorded
<br />during 24-hour periods (actual duration of
<br />storms unknown). In a 2-hour period in
<br />another loeation in the region, 2.15 inches
<br />were recorded. A standard project storm' for
<br />Leach Creek, Horizon Drive Channel. llnd
<br />Lewis Wash was developed from estimates of
<br />probable maximum thunderstorm precipita-
<br />tion based On recorded thunderstorms in the
<br />region. The standard project storm,
<br />designated as 40 percent oithe 3-hour
<br />probable maximum storm, was centered over
<br />the drainage basins of the threc tributary
<br />streams, The IOO.year and 500-year storms
<br />were developed using precipilalion-frequency
<br />curves based on regional precipitation data
<br />recorded in the western states.
<br />Lossratesforthetributarydrainagebasins
<br />
<br />OBSTRUCTIONS
<br />Natural obstructions to l100dflow include
<br />trees, brush, and other vegetati(ln growin!!:
<br />along streams. During floods, vegetation
<br />impedes floodflow aIld result>; in backwater
<br />conditions and increased flood heights. Brush
<br />urtreeswashedoutduringfloodsandcarried
<br />downstream could collect on bridges or pluJl:'
<br />culverts, thus creating a damming effect and
<br />overbank flow_As f100dflow increases, masses
<br />of debris can destroy a bridge or eause.....ater
<br />levels to rise higher and mOre rapidly than
<br />normal. thus eroding and damaging
<br />
<br />I
<br />I TABLE 4
<br /> OBSTRUCTIVE STREAM CROSSINGS'
<br /> Ele.>lion'
<br />I Unde.. Topol IOO_yu, SOO-yea,
<br /> ldenllrlcallon locallon' Slrumbed cl,.,ance' Roadway' Flood Flood
<br /> COLORAOORIVER
<br />I Gr.adA.....nue(Sr..te
<br /> Highway :J.,lO~
<br /> Westbound!..>.n... ~85,:\.3 ,~. ~S59 4562 455.1 4555
<br /> e..\boundLanc. 385.56 ,~. ,~, ,~, "" ,ro.
<br />I ORGWRR 386.71 4546 4566 ~570 ,,~ 4Sl15
<br /> 5\hStr..\(U.S, 50),
<br /> Northbound Lan.. 356,8.1 4549 4570 4571> ,,~ 45!;fi
<br /> Southbound Lan.. 386.84 4550 4565 4572 4565 ''''
<br />I I 82 Road 398.05 4606 4625 ,~, 4627 ''''
<br /> LEACH CREEK
<br />I Ri.erRoad' 2.040 ,~, 4540 '"' '"' '"'
<br /> DRGWRR 2.100 ,~, 4541 4545 4544 4546
<br /> U.S.HighwayMW' 2.440 ,~, '"' '"' '"' 4547
<br /> I 6/50 Frontage Road' 2.626 4636 '"' 'M' '"' 4547
<br />I 24ji,Road' 9.890 ,~, 4574 4575 4574 4574
<br />, 25Ro.od' 12,530 4676 4587 4591 4590 4590
<br /> MolnL;neG..nd
<br /> V.neyCanal 13,630 "" 4594 4599 4593 .J594
<br />I G~ Road' 19,130 4627 "" "W '''" 4640
<br /> i-70 Frontlll"c Road' 19,540 4638 4646 4561 4660 4661
<br /> 26 Road' 21,330 ,,~ 4659 '"" 4664 4667
<br /> HRo.od' 22.570 .oM 4674 4684 4685 .oM
<br />I LEWIS WASH
<br /> I D"~ 2,070 4610 '''" ,,~ 4G~1 ,1623
<br />I Dl4Road 4.730 ,,~ "" 'M" 4639 4642
<br /> E.... 7.370 4644 4656 4660 4657 4661
<br /> G..ndV..lleyCan..1 8,120 4651 "" 4668 ,,~ 467~
<br /> I U.S. Hill"hway6/2~ 9.0<10 "" 4674 4618 467~ 4677
<br />I """' 10.030 4673 ,,~ 46&> ,,~ ,~,
<br /> ~'l\ Rnad 16.470 4737 "" ,,~ 4741 4752
<br /> lnlc..tat~ 7Q' 17.<>00 47~~ 47~q 4171\ 4770 4779
<br />I HORIZON DRIVE CHANNEL
<br /> Pri"~te Crosoi"ll"' ,.,.. "'" ,~, "" 4691 4591
<br />I I PrI..tcCt"",ing" 9,761l 4:;S8 4594 ,,~ 4696 4596
<br /> 26 Road' 10.400 4597 ""' ,., ""' 4607
<br /> 26\lRoad' 13,461l 4618 4628 '''' 4n35 46::16
<br /> M~in LineG.and
<br />I V~l\~' C",,~\' 14,260 """ ,~; '''' 4635 1611
<br /> Gran(!Van.y![;gh-
<br /> !ineCan..I' 16,700 4645 'M' 4658 4559 "M
<br /> llori.onOrive' 16,5-10 4643 ,,~ 4651 4660 4661
<br />! 27 Roa<l' 17.440 4657 4662 '''' 4670 4671
<br /> GRoad' 19,900 ,,~ ,,~ 'M 4703 ""'
<br /> 'C.Ivo......M.l."".....b,..,
<br /> 'A''''''.flo''''..r....r'....'''''''"..'"".,,'r...'''..t'''..I''''l....,........''''''..<V..'IooCM'.....,to".,,,,,",",
<br /> 'Mil.."p.l...""'""'1<<.F"'r.~,iID,.._""'Coto".,.RI..r:I"'"o>""..I""".."""'''''"b.'.'>'''N..m,.
<br /> '(_....lot.......'""'''.."..,''',,,Io...I'',,..,.rh,;d'''..''p<...~.Too,f....''.''''';J~,.,..,,,,,,"...aod
<br /> ""I"....
<br /> .A'......"',h,..'.-l;."mOOl...'y.....u....."'lw....""'""
<br />
<br />
<br />were estimated due to limited "treamflow
<br />data with which to reproduce cloudburst
<br />floods. Hydrologists familiar with the area
<br />established loss r..tes based on precipitation
<br />data for Grand Junction and predpitationand
<br />streamflow data for similar basins in other
<br />parts of the region, with consideration given
<br />to topography, ,'egetation, and wil conditions.
<br />Loss rates adopted for the 100-and 500-year
<br />cloudburst floods were 0.15 inch initial loss
<br />and 0.20 inch per hour constant lo~s on the
<br />tributary streams, The resulting flows are
<br />eontained in TableS.
<br />InformationonlO-and50.yearfloodevents
<br />was a\sodevelopod as part of the hydrologic
<br />studieseonducted for this report, These would
<br />basically be snowmelt floods on the Colorado
<br />and Gunnison Rivers and cloudburst floods on
<br />the tributary streams, but, with the exeeption
<br />of showing their water surface profiles on
<br />Plates 58-74, are not fllrther eovered in the
<br />report.
<br />
<br />
<br />
<br />
<br />
<br />
<br />abutments. approach"", and the overlying
<br />roadbed.
<br />In gcneral,obstructions restrict floodl1ows
<br />:wd may cause overbank f1ows,unpredietable
<br />areas of flooding, lJOSsible damage to Or
<br />destruction "' uridgc~ ,,'u.I "ther stream
<br />crossings, and increased velocity of flow
<br />immediateiy downstream. Most qf the stream
<br />erossins;s in the study area are obstructive to
<br />fToodflows. Pertinent data on aU structures
<br />are shown in Table 4. The effeetof obstruc-
<br />tion" may]x, "cen on Plates ~8-14.
<br />
<br />
<br />
<br />. Th. '''''m ...."IHog from the mosl sc'"<'" combin.tion of met""'~'>I(k"I condition. 'h.l $'" ",",kh,,....1
<br />r''''''''.b1r<o''act''i,lioolthcg''''val>hio.I..eain ,,'hich.'tr1Xtrnw.ioi,I",,"to<!,
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