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<br />002465 <br /> <br />channel depth and above average surface streamflow velocity. Pools were identified as <br />segments between riffles with larger average depth and lower surface velocity, <br />Reclamation also collected data describing the size and thickness of bed <br />sediments in Glen Canyon in 1956 (Pemberton, 1976). Bore holes were drilled through <br />the alluvium at seven locations. Drill logs and samples detail the thickness of the <br />overlying fine-grained sediment and the size distribution of the underlying gravels. Ajet <br />probe was used to penetrate the fine sediment layer and determine the depth to gravel at <br />an additional nine locations. At each ofthese locations, the jet probe was used to <br />determine the depth to gravel at multiple positions across the channel. Some of these <br />profiles of the gravel interface were located at or near the monitoring cross-sections. <br />From these data, we reconstructed the longitudinal profile of the sand-gravel interface in <br />Glen Canyon to place the history of bed erosion in the context of bed-material size. <br /> <br />Lees Ferry Gaging Station <br />We also analyzed the records of bed topography for both the Upper and Lower <br />Cableways of the USGS Gage at Lees Ferry (Figure 1). Water surface elevation has been <br />measured by a recording gage that has been maintained at the same location since <br />January 19, 1923. From 1921 to 1923, water surface was measured at several different <br />staff gages, The details of the gage operations and discharge measurements, including <br />estimates of extreme floods, are described by Topping et al. (2003). Topping et al. <br />(2000) analyzed the record of bed elevation up to 1962. We extend the record to 2000, <br />including changes caused by the closure of Glen Canyon Dam. <br />Discharge measurements have been made at three different cableway locations <br />(Figure 1). The Upper Cableway was in operation from August 3, 1921, to December 1, <br />1966. The Lower Cableway was installed in January 1929 and removed in February <br />1965. From 1929 to 1965, the Upper Cableway was used for most measurements and the <br />Lower Cableway was used primarily during floods when measurements at the Upper <br />Cableway were logistically difficult. The Upper Cableway is located 1.5 km upstream <br />from the gage and is the same cross-section as Reclamation's cross-section R-l. The <br />Lower Cableway was located 0,7 kIn upstream from the recording gage. Since December <br /> <br />15 <br />