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3 <br />width at 15 fixed transects on photographs from 1964 and 1978 (see figure 2a) <br />and reported a 13 percent decrease from 700 feet to 610 feet. Andrews chose <br />relatively straight reaches of channel and selected cross sections without <br />midchannel bars where change was most easily measured (Andrews, pers. cornet., <br />1989). <br />For the same photographic interval, Pucherelli found a decrease in average <br />channel width of 15 feet, from 693 feet to 678 feet, for a 20-mile reach of <br />the Green that encompassed the transects that Andrews measured. The pro- <br />cedures used by Pucherelli integrate the entire range of channel conditions for <br />a reach including midchannel bars, point bars and channel constrictions. <br />For the lower study reach, Andrews measured channel width at 14 fixed tran- <br />sects on photographs from 1952 and 1981. His data showed a decrease in <br />average channel width of nearly 10 percent from 515 feet to 465 feet. <br />Pucherelli reported a decrease in average channel width of nearly 5 percent <br />from 473 feet to 453 feet for the same period (see figure 2b). The length of <br />channel studied below Green River, Utah, was essentially the same for both <br />studies. <br />The discrepancy between Andrews average channel widths and those reported by <br />Pucherelli are likely due, in part, to the different methods of analysis. The <br />delineation of channel area for a long reach of channel presumably provides <br />the best estimate of average channel width. <br />For the upper study reach, the similarity of the average channel width estima- <br />tes for 1952 and 1964 supports Andrews conclusion that the river was in a <br />quasi -equilibrium condition prior to regulation by Flaming Gorge. Also, the <br />close agreement of the average channel width estimates for the 1974 and 1978 <br />photography suggests that the channel had reached a new equilibrium width by <br />1974. Between 1978 and 1986, average channel width increased by 2 percent. <br />At the lower study reach, the similarity of the average channel width fnr, <br />1952 and 1974 suggests that the adjustment in channel width ocr?,rred later at <br />this site than in the upstream reach. The decrease in channel width betWepn <br />1974 and 1281 appears to represent an adjustment in width to regulation by <br />Flaming Gorge. Between 1981 and 1987, channel width changes increased a <br />slight amount in the lower reach. The maximum change in channel width in the <br />lower reach is about 20 feet, which corresponds to the presumed accuracy of <br />thetpho _toigterpretation. <br />Discharge Patterns <br />Andrews [31 studied the discharge records for the Geological Survey gauges on <br />the Green and determined that no change in mean annual flow occurred following <br />closure of Flaming Gorge. However, he demonstrated changes in the flow-dura- <br />tion pattern of the Green, reporting that the magnitude of flows that occur <br />less than 10 percent of the time were significantly decreased after regulation <br />for the Jensen and Green River, Utah, gauges. <br />The annual peak flows for the Geological Survey gauge near Jensen for the time <br />period covered by the aerial photography are shown in figure 3. The peak