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<br />002481 <br /> <br />Aggradation of the deposit at the Lower Cableway appears to have been initiated <br />with the deposition measured in 1935. Although the period of record prior to the <br />aggradation of the 1935 deposit is short, notes from the Lees Ferry hydrographers log <br />support the conclusion that narrowing began at that time. On June 4, 1935, the <br />hydrographer, Sherman O. Decker, noted channel narrowing in the vicinity of the gage <br />and upstream caused by flash floods that occurred the previous summer: <br /> <br />"The measurements above 42,000 c.f.s. have been plotting from .06 to .21 <br />[ft] above the rating curve dated 10-15-32. An investigation at the river <br />banks at and above the gage was made and it was found that the extremely <br />heavy runs of last summer had caused several washes which empty in on <br />the right bank and from 100 to 600 ft. above a point opposite the gage, to <br />build deltas out in the river. This narrowed the main river channel and <br />also turned the flow slightly more towards the gage. Since these deltas <br />and a heavy growth of willow have not scoured out it is believed they are, <br />at least partly, responsible for the measurements consistently plotting <br />above the curve." <br /> <br />~>.<"'\;V"_. : <br /> <br />In addition to noting the deposition and channel narrowing that began in 1934-35, <br />the hydrographer also notes the stabilization of those deposits by willow. Both the 1935 <br />and 1952 aerial photographs show a vegetated deposit in this location, although by 1952 <br />the vegetation was likely dominated by the tamarisk that now cover the deposit. <br />The total amount of channel narrowing that has occurred at the Lower Cableway <br />between 1935 and 2000 has been about 8 m, all of it occurring on the left bank. This <br />represents a decrease in the width of the river at this location of about 4%. Thus, the <br />major episode of channel narrowing (50 m) reported by Hereford et aI. (2000) between <br />the 1920s and 2000 in the vicinity of the Paria River confluence Gust downstream from <br />the Lees Ferry gage) did not extend this far upstream on the Colorado River. <br /> <br />Alluvial Deposits in Glen Canyon <br /> <br />Glen Canyon in 1952 <br />Although sheer bedrock walls and steep talus slopes are the most striking feature <br />of the river corridor in Glen Canyon, channel-side alluvial deposits have also been a <br />persistent feature of the fluvial landscape. Aerial photographs taken in 1952 show <br /> <br />31 <br />