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<br />The current logging interval is 20 minutes. Monitors are downloaded, serviced, and <br />recalibrated on a montWy basis. Monthly chemical sampling for nutrients and major <br />ions, and biological sampling for cWorophyll, phytoplankton, and zooplankton is also <br />performed inside Glen Canyon Dam and at Lees Ferry. <br /> <br />Three stations are currently monitored. The primary point of measurement for Glen <br />Canyon Dam releases, Colorado River below Glen Canyon Dam (CRBD), is located in a <br />perforated pipe attached to the concrete wall below the hollow jet tubes of the river <br />outlets works, approximately 50 meters downstream of the generator outlets. This site <br />shows effects of reaeration of releases from turbulence in the tailrace, adding noise to <br />dissolved oxygen readings. Because of this, an additional site, Colorado River at Glen <br />Canyon Dam Draft Tube (CRDT), is located inside the dam and samples water from one <br />of the dam's eight draft tubes, immediately below the generator turbines. Water is routed <br />to the recording instrument through a closed flow cell before any atmospheric exposure, <br />This site is prone to periodic generator shut downs and therefore is not a reliable site for <br />continuous monitoring but it provides more accurate information on the actual dissolved <br />oxygen concentrations of dam releases. <br /> <br />The third site, Colorado River at Lees Ferry (CRLF), is a mid-channel buoy deployment, <br />sometimes prone to changing flow velocities and algae and debris collecting or growing <br />on the instrument, complicating interpretation or verification of dissolved oxygen <br />readings. <br /> <br />Due to quality assurance problems with pH and dissolved oxygen measurements, which <br />are described below, four YSI Model 6920 multi-parameter sondes were recently <br />acquired and deployed. These sondes are capable of measuring turbidity in addition to <br />the other four parameters, do not have the flow sensitivity of the Hydrolab Recorders for <br />dissolved oxygen measurements, and may have reduced pH drift. Performance of these <br />units will be evaluated as comparison data become available. <br /> <br />Results <br /> <br />Historical Patterns and Trends <br /> <br />A yearly cycle of temperature and conductivity patterns in Glen Canyon Dam releases is <br />shown in Figure I <br />. . <br /> <br />10/25/00 <br /> <br />DRAFT <br /> <br />2 <br />