7645

• UCREFRP Catalog Number: 7645
• Author: Harvey, M. D. and R. A. Mussetter.
• Title: Mineral Bottom Geomorphic Investigation Trip Report.
• USFW Year: 1992.
• USFW - Doc Type: Ft. Collins, CO.
• Copyright Material: NO

. 12/(\7/92 14:61

'&303 945 8799

COLO RIVER DIST ~~~ USFWS RIP DNVR

banks.. Mass failure of the banks also C3l.lSeS lWnC'Y2I of tf1e bank vegetatfan in wt8t C1ppears to be 8
~ feedback mecharism. Slncethe und~ d1hsbmks (the rr~,,"i$m that steepens
the bank angle) occurs during reIad'wIy low ficms. I can be argJJed that the increased dur.ition cI mid
range taNS ~ dam ~ on the Green RiVer (Andrews. 1986) has increased the tate at
whfe;h the tanmf*.1s being relneJ'IC.

2) 'a.nnet.C8pcIci\y

DetmnirAdion dthe freqtJ8ncy ofowrbank tI~ ;long the sludy reach dthe QI'Mt\ Rrver
Is depemert an beir1J able to define the channel c:spaci;Y. To achfeve 1hIs. a number of C(OSI ~
wn~ d1I'fngthefiE!ld inspecticn. At Cotionwcod BoUom,.1ha USF'WS had esttished an IFlM
titQ In 1980 with the eddifiODCll purpose of having a ~ mcnItDring site to investigate
~degnId2dfan tmIX'lsinthisJeaCh of the river. Six CfQ$$ sedronswere surveyed, tiedtcgether
horizDntaIIy and vedIcaIly and .morwmented. betWeen RM 55 and AM 6S. The cross sec:tiClns were
5UIVe)'ed at c:IisctIiug"e& cf 10.000, 5.100 and 2,600 cfs. The pdted cross secdans (pRMded by Mr.
George Smith,. USFWS) dearly indicale 1hat tl'O:S$ sedion geomeby 1$ depend8nt on cfascharge. (Harvey
BnCl W~ 1_ Anthony and Harley. 1002) and that aggradstfon/dagr.Kiatian trends sixxJId De
~ only on ~ conducted at similar alSCharges. Cross Hdions (transects) 2, 3. 4, and 6 were
relocated and ~ on 14 May. 11ilS2:1t a cfischarge ofabout 9,500 '*- The plotted cross sections
are attac:hed. to thls report (Appendix A). IJ.so shown on the platted c:rcss secttons are the profiles for
the 10,000 c::fs IUIWY In 1980y Comparisons of 1he prcfiIes fr1di~ 1hat there ha5 been very Iittte
changB at Bm/ of tI\a cross sections ather tThi..1'\ what Is to be expected 91\91 the minor differenceS in
dischar;e between the Z SUfV~

Crass sections were also surveyed at 8 locations at Unknown Bottom between AM 28.5 and AM
31-3- The ~~ portions of the cress s!actions were rec:aded on a fathometer trace and Iat:er
digitized. Obsefvatfor.s (if the bank heights and inclinations were made as well and the surveyed bank
~es for1he CoItamvood Bottom cross sections Wen) ~ to the ~ cress sedfons
(on the basis of Iccaticn w<<hin the bend) i1l: the downstream locatfon. CrQ$S.section st:a:ticnir4. and
henclG 1ho horizontJl rn!af:ionshlp between 'the sections was awroxfmated from 1he tcpogr.!phic map.
(The ~ .slope 'I'r..s <JlSQ apprmcfmated from the tcpagmphic maps at the Unknawn Boltom
1oc:at1on.) The pfofted cross secUcns me attIched to this report (AppendiX 8).

The stBYt!.)'Sf C'tISS sec:lJcns at.: the two locaIians were used 10 create HEC2 rnodI3I8 for erach
of the reaches. II. !he Coltolawood Bottom recdl. the bankfUI: dischaIge fer the 1ndMdU31 c:rosa
sectians r&ng&d from 34,000 to 22,000 cf.i fur i1 Mannlng's n w1ue d 0.D3 and from 29.000 to 19,300
cf$ fOr an n w.llua cZ 0.035. Average values for the reach. were 32,980 and 2B,1rrt cis fer n valuea
of 0.03 and o.oss, respectively. At tho Unknown Bot:tcm reach the bankfuI[ d"l9Charge for the individual
CI'OS5 sec:tioM ranged fron141.000 to 34,000 cis for an n value ci 0.03, and 41.900 to 30,200 cfs;'ior
an n Vllue ci 0.03S. Average wEu= fm" the rt:aCh were 36,240 cmd 32,B) c:fs fer n w1Ulid of 0.03
and 0.035. respedlVeIy.

To d*tmIne the fr~ of inundtltion of the bcItomIar1dI. a flow duradon curve \WS
developed from mean daily flaws. for the Grer.!1 River at the Green RIver, tnm gaging station fa' the
period 19S3 to 1980 (Figure 1). AIsc shown on the figure is the low duration CiUI'W for the peried
between 1963 and 1982. developed by Andr~ws (1986). Comparison of the curves demonstrates the
effeds,cfthehigh.discharge YeaJ'S gf 1S83, 1S"54 and 1886 on the upper end Qftf1e ffow dumion curves.
At thr;l CQtlcnwoorj Bcttcm reach, the exceroence frequencies' for the resch ilVRl'SSecI bankfull
discharges are 1.3 percent ar'Id O-S pen::ent fur n values d o.oa and O.Q35, reapeclM3ly. The
exceederx::e frequencie$ trnnsIate into 4.7 GOO 2.9 day$ per yaar. No the UnIcnawn Bottom ~ch the
exceedence ~ for the reach avemgo b3nkf1.dI d"JSChacges are 0.4 percent and 0.3 percent for
n valuesdo..Cl3 and 0-035. respactiveIy. Theexc:eedence~tmnsIafe into 1.5 and 1.1 days
p&ry&;r. The exceedence. frequencies represent awmse valUes and they do not 1ndtcate thal bankfull
di$ch;lrge is l;'Y(':eE'dm fNery year. In fuel:, as the next: ~h snows, bankfull discharge at the 2
sita9 has a retwn period of bmween 4 and 10 years.

3 Re5OtlI'Ce Consultants &. Engineers, Inc.

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