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<br />002390 <br /> <br />and is probably less effected by normal dam operations than other chemical and physical indicators. <br /> <br />Therefore, although these samples may prove valuable in identifying water quality effects and <br /> <br />trophic linkages, their analysis has not been incorporated into this assessment. <br /> <br />2. Glen Canyon Dam Releases <br /> <br />a. Hydrologic Data <br /> <br />Data to quantify the amount of water discharged from Glen Canyon Dam comes from two main <br /> <br />sources. The most immediate source is powerplant releases from Glen Canyon Dam. These data are <br /> <br />the result of powerplant hydropower generation, integrated on an hourly period, and converted to <br /> <br />discharge in cubic feet per second (cfs) depending on generator rating curves and powerplant head. <br /> <br />These data form the basis for meeting the operational constraints set by the Glen Canyon Dam EIS <br /> <br />and Record of Decision. Data exist from 1965 to the present and separate powerplant release from <br /> <br />those of alternate spillway and river outlet works structures (U. S. Bureau of Reclamation, 1921- <br /> <br />1997). <br />The other source of hydrologic data is the U.S. Geological Survey (USGS) stream gage, Colorado <br /> <br />River at Lees Ferry, AZ (09380000). Discharge data is obtained every half hour from satellite <br /> <br />telemetered stream gage measurements applied to a discharge rating curve. These unit value data <br /> <br />begin in January 1985 and continue through the present. Daily values exist for the Lees Ferry gage <br /> <br />from October 1921 and are used to represent pre-dam conditions in the Colorado River (U.S. <br /> <br />Geological Survey, 1985-1996) <br /> <br />b. Time Series of Physical Parameters <br /> <br />The varying quality of Glen Canyon Dam releases were studied using data from two sources. The <br /> <br />USGS has maintained water quality monitoring for salinity and specific conductance at the <br /> <br />Colorado River at Lees Ferry gage (09380000) since 1944. These data exist in USGS daily values <br /> <br />06/02/98 <br /> <br />DRAFT <br /> <br />Po' 130f62 <br />