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<br /> <br />002281 <br /> <br />such as power production, water delivery, cultural and historic resources, recreation and public <br /> <br />health. <br /> <br />While direct linkages exist among these resource categories, identification and evaluation of <br /> <br /> <br />effects to all these resource categories is impossible within the current time-'lonstraints, budget <br /> <br /> <br />setting, and data limitations. The scope of this assessment will therefore mainly focus on the <br /> <br /> <br />various physical and chemical water quality attributes associated with Glen Canyon Dam <br /> <br /> <br />operations for which information has been or is currently being gathered. <br /> <br />II. Background Information <br /> <br />Concurrent with historical changes in dam operations and reservoir conditions, Reclamation <br /> <br /> <br />has maintained a water quality monitoring program on Lake Powell since 1965. By associating <br /> <br /> <br />the monitoring effort with historical dam operations, increased understanding can be gained of <br /> <br /> <br />effects of dam operations on reservoir resources. <br /> <br />A. Brief History of Lake Powell and Glen Canyon Dam Operations <br /> <br /> <br />Lake Powell has had a relatively short existence as an operating reservoir. Its history can be <br /> <br /> <br />described in terms of three major periods in Glen Canyon Dam operations. <br /> <br /> <br />1963-1980. The seventeen-year period from 1963 to 1980 resulted in the eventual filling of <br /> <br /> <br />Lake Powell to its normal pool elevation of 3 700 ft. With minor exceptions, this period was <br /> <br /> <br />characterized by constantly increasing reservoir elevations, increasing depth of the penstock <br /> <br /> <br />withdrawal zone, and continual inundation of new areas of the reservoir basin. Stable <br /> <br /> <br />stratification patterns in temperature and salinity developed from the constant withdrawal at the <br /> <br /> <br />penstock level. <br /> <br /> <br />1980-1990. Relatively full reservoir levels characterize the period from 1980 to 1990. A <br /> <br /> <br />succession of high runoff years in the early and mid 1980's brought the reservoir 8 feet above its <br /> <br />03/06/98 <br /> <br />DRAFT <br /> <br />Page 5 of 62 <br /> <br />