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<br />OO~289 <br /> <br />Chemical analysis is frequently the only way to determine the quantity of certain substances in <br /> <br />solution, such as nutrient compounds, <br /> <br />c. Biological Samples <br /> <br /> <br />Biological monitoring in Lake Powell was.init.iated.in-J.99Gto>attempt-te-establisha link <br /> <br /> <br />between chemical and physical characteristics and higher trophic levels. The analysis of these <br /> <br /> <br />samples has not been fully completed. Furthermore, most biological activity in Lake Powell that <br /> <br /> <br />would be identified by the analysis of zooplankton and phytoplankton samples takes place near <br /> <br />the surface and is probably less effected by normal dam operations than other chemical and <br /> <br />physical indicators. Therefore, although these samples may prove valuabie in identifying water <br /> <br />quality effects and trophic linkages, their analysis has not been incorporated into this assessment. <br /> <br /> <br />2. Glen Canyon Dam Releases <br /> <br />a. Hydrologic Data <br />Data to quantify the amount of water discharged from Glen Canyon Dam comes from two <br />main sources. The most immediate source is powerplant releases from Glen Canyon Dam. These <br /> <br /> <br />data are the result of powerplant hydropower generation, integrated on an hourly period, and <br /> <br /> <br />converted to discharge in cubic feet per second (cfs) depending on generator rating curves and <br /> <br /> <br />powerplant head. These data form the basis for meeting the operational constraints set by the Glen <br /> <br /> <br />Canyon Dam EIS and Record of Decision. Data exist from 1965 to the present and separate <br /> <br /> <br />powerplant release from those of alternate spillway and river outlet works structures (U. S. <br />Bureau of Reclamation, 1921-1997). <br />The other source of hydrologic data is the U.S. Geological Survey (USGS) stream gage, <br />Colorado River at Lees Ferry, AZ (09380000). Discharge data is obtained every half hour from <br />satellite telemetered stream gage measurements applied to a discharge rating curve. These unit <br />value data begin in January 1985 and continue through the present. Daily values exist for the Lees <br /> <br />03/06/98 <br /> <br />DRAFT <br /> <br />Page 13 of 62 <br />