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,'12/~7j92 14;~2 '&303 945 $799 COLO RIVER DIST ~~~ USFWS RIP DNVR Ffsan 2 shoM the peak fioWfrequency ~ (best fit and 95 percent confidence (nl:eMI) fQr the period fmm 1953 to 1990 at the Gr&ilh HlVer gage. Depending on the n wIue used (0.03 or 0.035) ;at; the CQII:cnwocd BdtDm reach. the bankfuD timcharge has 8 frequency of 25 to 28 percentwhicb at!: eqUi\laJent to return J:*fods rJ between 4 and 5 years. At Unknown BoUcm. depencrq on the n wlue used (0.03 IX' 0.035). the bankfull dischalge. W a frequenc.y d 14 to 20 per=r4 \'Vhlch ere equIvalent to r-.m pIVIcxIs,af between 5 and10~..Jn contrHt. Figure 3 shews the peak flow hquancy CUN8J (bOstftt One ar1dB5 percent canfic:Ience"intel'M) for U1EI pertxI frcm 1894 to 1Q62. Dependtng OD the ,.n varue.used lO-03 or OJl35) ..th8 CQII:cnwocd Bottom IWCh,If1e IxmkfuIl cflSCharge tw;l frequenGyof 60 to 58 percentwhtch ana equIvalent to . relum pWiocf d ~ 2 years. N.lJnIcnoWn Botkxn the ban1cftJII dTscharges have freqUendes from 36 to 50 percent whlch are equfwlent 10 reIum periods of2 to 3 years. . '.'. The frequenq and retum pedact. data obviousfy do not "* any allowance for ch9nnel morphdoglc Changes that may ~ tM;Ien ~ by the e$labrsshment of tamarisk (Gear, 1978). If tn fad: Onts 'interpretation is correct, the frequency of overbank flows wauld haVe been loWer priorta 1118 edvent of ~ . . 3) Haf:lifat UtiIimtian Potential Hkltorfcal fish catch d:rta Indic:ite that juvenilv. Colorado Squawfi!:h are abuhdant In the lower Greerl RIver (G. Smfth, USFWS Memo. to Channl'1.d Manitat'ing Crew. 1992) which tends to suggest that thel'9 Is adequate fuv;nle ~ In the reacl1. Since the CoIcndo sqrmwfish'8pilMl all the recessional limb or the ~ hytI~ (Tyus and Karp. 1989). and the larvae are distributed dcwnsb'eam by drift it is poss1b1e that the rnocfification dthe IIowdur.Jtion cwve (seeArfjrews. 1985) has had an Impact an the JaMJ c1rift:distJnce. Squawfi!h are kncwn to $pawn in canyoh-bound reaches of the lower Yam,. River (Tyue end ~, 1989) and in Desolation C'.nyon (E. WICk. pelS. ccmrnunfcation) onthaGreen River. Ifthetimtng oflmwl emergence coincides with the longer duration tn'id-rarlg(;l ft(l'lNt;, the larvae co1Jd in fact be mnied farther downGtI'rmm than wautd have or:.curred picrto flaw regulation.. With a ~cwer channel, 'the flow depth for a ~e of cIIsd14lrge$ foIJCNling larval emero~nce wm: be hIgher 8IU It Is ttlerefore conceivable that there Will be lest sI8ckwat<< h-:lbif4lt fer the Imvae. Because of !he magnitude of the bBnkfuII capacii;y and1he fad thal: sqtJaWlmh 9~. &ft&r' the",enk dJsc:harge.. out-ot'-bank hsbftat will rarely. If ~ be. awiIabIe to larval squawfish Tn the~awerGreen Ftlver. Inaeased pO$l-em<<genc8 release:s from Flaming Gorge reselWlrwBI tend to be courd:erprcduc:Uva with respect to the laval stage of the squawfish. . . The RazorbJck sucker $pawnsCR the lisihg funb of 1he BMUCIl h)drcgraph (ryus and f<'#rp. 1989) and awears to have a f3irly limitl;ld nurn:bm- of spawning loc:aticM on th;I upper Green River and 1he IowerYampa Rivet (Tyu!1 and Karp, 1990). laMm ma also disper8ed by a drift mechanism. bUt I flOW$ following 1mvaI emergen~ exceedbanW ~ is a potential for1hem to util~ 1he DUt.m.fmtk habiI3t In ths reach of the Green RIVer ~t is the subject of this report (RM 120 to AM Z8) Uu, frequency of exceedBl1C8 of Um bahJCfuIl <lISdWgc Is lew. If it Is assumed that the bar1;kfuII C3P3clty estimates fer Cottonwccxi Bottom alxI Uriknown Bottom are ~y representative fer the bottomarxls downstream of AM 97 (ccn1Iuenre with San Rafael River) then It is 3Iso reasonab1e to condude that in most yearn Bny Razorback sud~er larvae th3t enter the reach will be passed througtr the reach. If flow releaRlS from Flaming Gorge. reS8fVOir fail to increase the total dischal{le in the river to the point where the I:lankfurr discharge Is ~~ for whatever period Is required for successfU overbank habitat utlizition, the increa:ied 1I0\vs will merely in(:rease the larval drift rate and di$mCL 4) Recommenda(loflS 1. l11e channel cep;cl1y ~ :Jt both Cottonwood and UnknoWI\ Bottoms and 1he flow dunlUor ' . . and Ifooc:I ~ ~ Jndlc:ate that the rawer reaches cI the Green River are unlikely to. btt d great: s1gnific;nce in terms of Aazcnmck. SUcker ~e habitat. Therefore. there doe$ not appear to be rnw;!1 value in futuro cl13nnel ~ - overbank flaw rncnitoring. 5 Re50Urce Consultants & Engineers, Ino. ~007 .~ .~ ;~ :'-- i