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<br />PITLICK AND CRESS: DOWNSTREAM CHANGES IN CHANNEL GEOMETRY 34 - 3 <br />Ie30 1WOO 10e3d 108,00 <br />39°3© <br />39'{ 6 <br />38°30 <br /> Rulison <br /> <br /> RD <br />0g <br /> ? <br />?y O <br />? <br /> C? Geaeque ???r <br />fl <br /> i ? <br /> 9056500 <br /> Lorna <br /> i cc <br /> 9' G_??C11 Grand <br /> txx Junction <br /> <br /> IBM KEY <br /> 1-$719 <br /> RD Rifle-DeBeque <br />Cusco <br />- <br /> i <br />©C Drt ue - <br />,/A <br /> 15M I`-:Ale (leach <br /> CF T5'M to MIIC peach <br /> RH `r[uoy HOrsemtat Cyn <br />? <br /> "? A^:V1 'ilC:?ri•IStE? <br />} <br /> '?1 1 of Cii o-Fish Furst <br /> DW L`avey <br />PV p ?t PV Professor Va5ey <br />" <br /> 66 <br />NN as Big Send <br /> MV I rt fAV M=b Valley <br />? <br />- <br /> Moab <br />0 <br /> 0 10 2D 30 rrU <br />POW N <br />1 f ! 1 <br /> w <br />O 10 20 30 40 50 km <br />I W36 109,00 10e3d 10ecir <br />39 30 , <br />39"00' <br />3e3d <br />Figure 1. Location map of the study area and specific reaches of the Colorado River. The short lines <br />across the river denote reach boundaries and the seven-digit numbers indicate the locations of U.S. <br />Geological Survey (USGS) gauging stations. <br />logistical reasons (e.g., they were located across rapids or <br />densely vegetated islands). Cross sections were surveyed <br />using a total station and a motorized raft outfitted with a <br />depth sounder. To survey a cross section, the total station <br />was set up over one of the endpoints. Distance readings <br />were then taken along the line of the cross section by <br />targeting a reflecting prism on the raft; at the same time, <br />the person operating the raft would record the depth and <br />relay the reading by radio to the person on shore. Bank-full <br />levels were identified in the field by the break in slope <br />between the active channel and the most recent floodplain <br />surface. In cases where this boundary was indistinct, we <br />sometimes relied on differences between mature and young <br />vegetation, and in cases where there was more than one <br />level (e.g., due to the presence of an inset bench), we <br />referenced the lowest surface which was not part of the <br />active cannel. <br />[it] Samples of surface and subsurface bed materials <br />were taken from exposed gravel bars at low flow. Water <br />depths limited us from sampling the deepest portions of the <br />channel, and we avoided sampling on bar tops; the majority <br />of bed material samples were taken from portions of active <br />gravel bars that were inundated annually. Surface samples <br />were taken by randomly selecting 100 or 200 particles <br />(Wolman method) and determining their sizes using a metal <br />template with openings equivalent to 1/2 phi sieve sizes. <br />Table 1. Geomorphic Characteristics of Specific Reaches of the Colorado River <br />Reach Name and Location Reach Typeb w, m h, m slope Dso, mm <br />Rulison-DeBeque (rkm 365-328) A 114 2.45 0.00196 58 <br />DeBeque Cyn. (rkm 327-300) QA 77 3.12 0.00150 52 <br />15-mile reach (rkm 298-275) A 134 2.54 0.00175 58 <br />18-mile reach (rkm 274-246) A 175 3.01 0.00130 54 <br />Ruby-Horsethief Cyn. (rkm 245-206) QA 129 3.64 0.00100 44 <br />Westwater Cyn. (rkm 205-182)` B - - 0.00258 <br />Cisco-Fish Ford (rkm 180-153) A 147 4.49 0.00066 38 <br />Dewey (rkm 151-140) QA 132 5.14 0.00047 35 <br />Professor Valley (rkm 138-126) A 203 4.61 0.00149 69 . <br />Big Bend (rkm 124-113) B 106 6.43 0.00098 63 <br />Moab (rkm 111-105) A 151 5.13 0.00034 25 <br />'Locations of reaches are given in river kilometers (rkm) upstream of the Green River confluence <br />b A indicates alluvial reach, QA indicates quasi-alluvial reach; B indicates bedrock-bounded reach. <br />'No measurements were taken in Westwater Canyon.