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<br />002287 <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 />variability, and describe unusual conditions associated with reservoir operations or other factors. <br /> <br />Water quality data is present in the form of surface observations from a site visit, profiles of <br /> <br />physical parameters through the water column, and the results of laboratory analyses of chemical <br /> <br />samples. Hydrologic data was acquired to build a database of historical inflows, reservoir contents <br /> <br />and surface elevation, Glen Canyon Dam powerplant releases, and non-power releases from <br /> <br />alternate outlets on Glen Canyon Dam to associate water quality changes with hydrologic or <br /> <br />operation patterns of the dam. <br /> <br />1. Lake Powell <br /> <br />a. Physical Promes <br /> <br /> <br />A large part of the assessment analysis is based on the evaluation of the profiles of physical <br /> <br /> <br />parameters collected on lake-wide surveys at each established station and monthly at the <br /> <br /> <br />Wahweap forebay station. These profiles provide fine detail of changes through the water column. <br /> <br /> <br />The increase to the number of main channel stations and the monthly frequency of forebay <br /> <br /> <br />sampling provides adequate longitudinal and temporal resolution, respectively, for the purpose of <br /> <br />describing vertical density gradients, longitudinal reservoir gradients, and the seasonal and <br /> <br />temporal variation seen in these patterns. <br /> <br />03/06/98 <br /> <br />DRAFT <br /> <br />Page II of62 <br />