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<br />0.:12378 <br /> <br />I. Introduction <br /> <br />The Grand Canyon Protection Act of 1992 requires the Secretary of the Interior to evaluate the <br /> <br /> <br />impacts of Glen Canyon DaITi operations on all affected resources. Although the primary <br /> <br />evaluation of these impacts are on resources downstream of the dam, concern has existed that <br /> <br />certain aspects of dam operations have the potential to affect various resource attributes upstream <br /> <br />of Glen Canyon Dam. <br /> <br />In January 1997, the Grand Canyon Monitoring and Research Center (GCMRC) presented to its <br /> <br />Planning and Transition Work Groups, a prospectus for assessing the effects of Glen Canyon <br /> <br />Dam?s operation on water quality resources in Lake Powell and Glen Canyon Dam releases <br /> <br />(Appendix A). This document will serve to define the scope and objectives of this study, and will <br /> <br />form the basis for review of the assessment process and results. <br /> <br />Three experienced reservoir limnologists from outside the federal government not currently <br /> <br />connected with GCMRC have provided critical review. Three federallimnologists provided <br /> <br />additional review from the Bureau of Reclamation and the U.S. Geological Survey. Final results of <br /> <br />the assessment will be reviewed by a Science Advisory Group and presented to the Adaptive <br /> <br />Management and Technical Work Groups. <br /> <br />A. Scope and Objectives of Assessment <br /> <br />This assessment is an effort to integrate existing data from current and past monitoring programs <br /> <br />on Lake Powell in order to evaluate the effects of various aspects of Glen Canyon Dam operations, <br /> <br />from 1965 to 1997, on reservoir and release water quality. Primary consideration will be made to <br /> <br />peaking power generation, operation of non-power release structures, and potential selective <br /> <br />withdrawal. An attempt will be made to identify other factors affecting Lake Powell such as the <br /> <br />existence and structure of Glen Canyon Dam, climatological factors, and i.nternal hydrodynamic <br />06/02/98 DRAFT . j 1 of 62 <br />