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<br />, <br />002337 <br /> <br />Several aspects of the historical data set proved very valuable to the assessment. Monthly <br /> <br />lake-wide reservoir surveys from 1971 to 1982 gave valuable information about the fate of <br /> <br />advective density currents through the reservoir. Consistent tailwater monitoring provided <br /> <br />information abol!t variation in Glen C~-Dam.releases..between monthly measurements.. The <br /> <br />current monitoring program in the reservoir is characterized by quarterly lake-wide surveys and <br /> <br />monthly forebay surveys and includes measurements with higher resolution through the water <br /> <br />column and along the length of the reservoir. These data have given much information to inflow <br /> <br />hydrodynamics, the effects of Glen Canyon Dam release patterns, and seasonal dissolved oxygen <br /> <br />dynamics mediated by biological and hydrological processes. <br /> <br />When past monitoring programs have focused on specific aspects of Lake Powell water <br /> <br />quality, the resultant database is less amenable to analysis of long-term trends or patterns. The <br /> <br />challenge of designing any long-term monitoring program is to consistently collect those data that <br /> <br />will be valuable to long-term and short-term analysis, at a level of detail sufficient to accurately <br /> <br />identify trends and patterns, while maintaining a reasonable expenditure of resources to allow for <br /> <br />the continuation of data collection. The direction of a program such as this must be flexible to <br /> <br />accommodate changes in political and financial climate and respond to new information needs as <br /> <br />more knowledge is gained. It is felt that the current monitoring program on Lake Powell provides <br /> <br />consistent data collection with a sufficiently broad-based scope while keeping expenditures at a <br /> <br />reasonable level. Within this context, the program can be modified to meet changing information <br /> <br />needs and objectives. <br /> <br />B. Assessment of Factors Affecting Water Quality Conditions <br /> <br />The assessment process showed that the water quality in Lake Powell is affected by a variety <br /> <br />of factors, none of which can be truly separated from the others except, perhaps, by artificial <br /> <br />scenarios presented to a numerical hydrodynamic model of Lake Powell. Model development for <br /> <br />03/06/98 <br /> <br />DRAFT <br /> <br />Page 31 of62 <br />