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<br /> <br />on~270 <br /> <br />Abstract <br /> <br />The effects of the construction and operation of Glen Canyon Dam have been studied, <br /> <br /> <br />documented, and manipulated in the downstream environment in Grand Canyon. Glen Canyon <br /> <br /> <br />Environmental Studies led 13 years of study that focused on addressing and mitigating the <br /> <br /> <br />adverse impacts of the Dam on that ecosystem. While data has been collected from Lake Powell <br /> <br />throughout its filling history, there has been no concerted effort to evaluate the impacts of dam <br /> <br />operations on the physical, biological, and chemical processes of the reservoir and downstream <br /> <br /> <br />releases. Using data from the 33-year history of water quality monitoring on Lake Powell, <br /> <br /> <br />primarily from Bureau of Reclamation efforts, we will begin to demonstrate the effect of dam <br /> <br /> <br />operations and other factors on the water quality and hydrodynamics of Lake Powell. Of special <br /> <br /> <br />importance are the historical record reflecting the flood years of 1980 to 1986, modified <br /> <br /> <br />operations of Glen Canyon Dam which began in 1991, the results from the Experimental <br /> <br /> <br />Beach/Habitat Building Flood of the spring of 1996, and most recently, the high sustained <br /> <br /> <br />releases starting in February 1997. No special data collection was designed to answer the <br /> <br /> <br />question, but rather, the stock of existing data was analyzed to provide the answers and to fuel the <br /> <br />questions that formed the assessment. The results show that, combined with other influences, dam <br /> <br />operations have an undeniable effect upon the stratification and mixing of the reservoir, and those <br /> <br />effects are consequently passed downstream through the dam. Not all aspects of dam operations <br /> <br />could be answered or analyzed under the scope of the nine months allowed for the assessment. <br /> <br />The experimental flood demonstrated the effects of using alternate structures for the release of <br /> <br /> <br />water, in this case, the hollow jet tubes that are positioned 100 feet below the penstock <br /> <br /> <br />withdrawal ports. The historic record of the 1980's indicated that the combination of high and <br /> <br /> <br />repeated spring floods and high and sustained discharge from penstocks as well as spillways and <br /> <br />hollow jet tubes caused substantial mixing of the reservoir. The recent spring's high-sustained <br /> <br />03/06/98 <br /> <br />DRAFJ' <br /> <br />Eage iv of62 <br /> <br />r <br /> <br />