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<br />002388 <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 Profiles <br /> <br />A large part of the assessment analysis is based on the evaluation of the profiles of physical <br /> <br />parameters collected on lake-wide surveys at each established station and monthly at the Wahweap <br /> <br />forebay station. These profiles provide fine detail of changes through the water column. The <br /> <br />increase to the number of main channel stations and the monthly frequency of forebay sampling <br /> <br />provides adequate longitudinal and temporal resolution, respectively, for the purpose of describing <br /> <br />vertical density gradients, longitudinal reservoir gradients, and the seasonal and temporal variation <br /> <br />seen in these patterns. <br /> <br />Temperature patterns lend information to warming processes, thermal content of the reservoir, <br /> <br />and density characteristics. Consistent temperature has been regularly collected through the <br /> <br />reservoir since monitoring began in 1964 <br /> <br />Specific conductance is an indicator ofa solution?s ability to conduct electricity, a function of <br /> <br />the amount of total dissolved substances (TDS) in solution. It is much more readily determined in <br /> <br />the field than a laboratory analysis for TDS and is therefore used as an indirect measure of salinity. <br /> <br />As such, specific conductance measurements give an indication of the chemical makeup of a parcel <br /> <br />06102/98 <br /> <br />DRAFT <br /> <br />Page 11 of62 <br />