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<br />002387 <br /> <br />samples for phytoplankton and vertical tows for zooplankton. <br /> <br />. 2. Monthly Forebay Sampling <br /> <br />Monitoring of the forebay of Lake Powell is performed monthly at the long-term Wahweap <br /> <br />station. This site has been sampled monitored throughout Lake Powell's history and is located in <br /> <br />the main channel at the confluence with Wahweap Bay, 2.4 channel kilometers upstream of Glen <br /> <br />Canyon Dam. Chemical and biological sampling similar to that for major stations on quarterly <br /> <br />surveys is also performed. <br /> <br />3. Tailwater Monitoring <br /> <br />Continuous water quality data collection is maintained at three locations in the Glen Canyon <br /> <br />Dam tailwater. The first and most long-term running station is a perforated pipe below the river <br /> <br />outlet works (a.k.a., hollow jet valves), immediately downstream of the Glen Canyon Dam <br /> <br />powerplant on the left wall. This site has been in operation since August 1980 measuring <br /> <br />temperature and specific conductance at intervals of two hours or less. Dissolved oxygen <br /> <br />monitoring was initiated November 1990; pH measurements were started July 1995. <br /> <br />A second station is near the USGS Lees Ferry stream gage (09380000), in operation since <br /> <br />October 1991, recording temperature, specific conductance, and dissolved oxygen. pH <br /> <br />measurements were added August 1996. <br /> <br />III. Assessment Process and Data Analysis <br /> <br />A. Data sources <br /> <br />The assessment process consisted of integrating water quality data from various monitoring <br /> <br />phases to describe historical and seasonal patterns and trends in the water quality of the main- <br /> <br />channel reservoir body and the Glen Canyon Dam forebay, identify seasonal and long term <br /> <br />06/02/98 <br /> <br />DRAFT <br /> <br />Page 10 of62 <br />