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<br />OQ2457 <br /> <br />Glen Canyon. Many of these resources may be affected by present and future dam <br />operations. The pre-dam terraces whose shoreward banks are inundated by current dam <br />operations contain many archeological sites that, if eroded, would be permanently lost. <br />Because sport fishing for introduced non-native rainbow trout (Oncorhynchus mykiss) is <br />very popular, Glen Canyon receives heavy day and overnight use by boaters traveling <br />upstream from Lees Ferry, They use Glen Canyon sand bars and alluvial terraces for <br />camping and as day-use areas. Tourists enjoy the canyon in one-day float trips from the <br />dam to Lees Ferry. In total, more than 50,000 visitors travel the Colorado River in Glen <br />Canyon each year (U.S. Department of Interior, 1995). Finally, the Glen Canyon trout <br />fishery has become naturalized and the condition of the gravel/cobble bed is, therefore, of <br />concern with regard to spawning habitat. <br />The richness of data available for the Glen Canyon reach provides the opportunity <br />to investigate several aspects of channel adjustment in detail, illustrating how some <br />elements of channel adjustment can be anticipated and planned for, while others may be <br />unforeseen. In this study, we examine the spatial pattern of bed degradation between <br />1956 and present, extending the previously reported post-dam record of bed elevation in <br />Glen Canyon by 25 years. The record of changes in bed elevation and channel width are <br />enhanced by integrating, for the first time, post-dam measurements with long pre-dam <br />records of bed elevation at two discharge-measurement cableways that were abandoned <br />shortly after dam closure. We also analyze pre- and post-dam aerial photographs to <br />describe the style, magnitude, and distribution of changes in channel-side alluvial <br />deposits. This analysis of multiple and detailed long-term records of channel form <br />illustrates a comprehensive story of channel adjustment that is rarely told in its entirety. <br /> <br />STUDY AREA <br /> <br />Phvsiof!rauhic Settinf! <br />In its course across the Colorado Plateau, the Colorado River has carved a series <br />of canyons, each distinguished by a unique suite of geologic formations exposed in the <br />canyon walls. The most resistant rock formations contribute to canyons with abundant <br /> <br />7 <br />