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<br />OOZZ78 <br /> <br />hydrodynamic processes, so that these impacts are not inappropriately associated with dam <br /> <br /> <br />operations. The assessment will rely mainly on data from the Bureau of Reclamation's long-term <br /> <br /> <br />limnological monitoring program on Lake Powell, the current monitoring program, implemented <br /> <br /> <br />in 1990 and currently maintained by GCMRC, and information.-fromother agencies and <br /> <br /> <br />institutions. <br /> <br /> <br />Several factors combine to limit the scope of this assessment. A relatively short time frame <br /> <br /> <br />was specified for completion of this study. Budgetary constraints limit the amount of financial <br /> <br /> <br />and human resources dedicated to this process. The quality and completeness of data from past <br /> <br /> <br />monitoring efforts may be insufficient for certain evaluations and may not have focused on <br /> <br /> <br />important affected resources. Some information has not yet been organized into a form that <br /> <br /> <br />facilitates analysis and some samples await analysis. Therefore, the scope of this study will be <br /> <br /> <br />limited to the analysis of those data which have been 1) consistently collected over a long period <br /> <br /> <br />of time; 2) are readily available for computer analysis; and 3) will most likely show the effects of <br /> <br /> <br />dam operations on the chemical and physical limnology of the reservoir. <br /> <br /> <br />In this context, the term water quality is used to include the various physical, chemical, and <br /> <br /> <br />biological attributes that characterize a body of water in terms of its hydrodynamic properties, <br /> <br /> <br />chemical composition, and the organisms that live in it. Its use is not intended to connote any <br /> <br />value judgments based on suitability for a given use. <br /> <br />B. Purpose of Assessment <br /> <br />The closure of Glen Canyon Dam in 1963 caused major changes to the physical, chemical and <br /> <br />biological characteristics of the Colorado River in Grand Canyon. These changes are well <br /> <br />documented and include the removal of sediment and the moderation of temperature, salinity and <br /> <br />other chemical extremes. Operation of the dam for peaking power generation resulted in the <br /> <br />removal of seasonal discharge variability and its replacement with daily discharge fluctuations <br /> <br />03106/98 <br /> <br />DRAFT <br /> <br />Page 2 of 62 <br /> <br />