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<br />002437 <br /> <br />or not gage height was measured at the cable gage, The details of these calculations are <br />explained in Appendix C. <br />Minimum bed elevations determined from the 1956 to 2000 Reclamation and <br />GCMRC surveys ofR-1 were added to the record derived from USGS gaging notes for <br />the Upper Cableway. The 2000 GCMRC survey of the channel cross-section at the <br />Lower Cableway was included in that time series. Elevations for all measurements were <br />reported relative to sea level (NA VD 1929). <br />Complete cross-sections were plotted for selected dates for the Upper Cableway <br />and the Lower Cableway, to show patterns of erosion and deposition across the entire <br />channel. For these dates, the measured vertical depth and position along the cableway <br />were recorded from the discharge measurement notes. Bed elevations across the entire <br />channel were calculated by the same methods used for calculating the elevations of <br />maximum depth. For most measurements, position along the cableway was recorded <br />relative to the same point. When this was not the case, position along the cross-section <br />was determined by matching stable topography on the left bank of the cross-section at the <br />Upper Cableway and on the right bank of the cross-section at the Lower Cableway. <br /> <br />Mauuin!! of Alluvial Deuosits <br />Mapping From Aerial Photographs <br />Only a few of the Reclamation cross-sections traverse sections where channel- <br />side deposits occur, and those measurements were not routinely made above the edge of <br />water. Thus, the topography of channel-side alluvial deposits was rarely captured by <br />cross-section measurements, and these data are not useful for systematic analyses of <br />changes in those deposits or the determination of trends in channel width. Yet, changes <br />in the patterns of channel-side deposition represent an important component of channel <br />adjustment. We describe these changes by mapping all alluvial deposits in the study area <br />on one series of pre-dam photographs and five series of post-dam photographs (Table 2). <br />Surficial geology was mapped on mylar overlays on the aerial photographs, while <br />viewing in stereo to interpret the relative elevations of the deposits. We digitized the <br />mapping into a geographic information system (GIS), using a digitizing tablet <br /> <br />17 <br />