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<br />. <br /> <br />'..~rtB 1,;:'" ',-,r::I r" <br />... - ;..:.. J,::,: ~3 U'=.Fl.IS <br /> <br />p. c <br /> <br />IV. Potential Future Mitigation Alternatives in Addition to <br />Modification of Discharge C=iteria <br /> <br />A. E~fec~s of "!JO c~ar:c;ell Al'(.er:IC1~ive <br /> <br />16. Question: What are the economic and envi=onrnen~al cos~s <br />(loss, mitic;a-Clon, legal, etc.) of -.:.he "No Change" al':.e=~a':.ive? <br /> <br />Comments: The null hypot~esis for this question would state <br />thac there are no significant economic or envi=onmental costs to <br />the "No Change" alternative. The research program presem:ed he:::-e <br />is designed to address the various downs::ream discharge <br />components to dete~ine their significance in the dynamics of the <br />canyon systeI:l. The "llo Change" alterna~i.,e will be add:::-essed <br />after the research program is complete. <br /> <br />a. Effects of Variable Intake Structures <br /> <br />17. QUestion: If a va:::-iable intake st~~ct~re is used on Glen <br />Canyon Dam, what will be the ef~ects of int3ke at various levels <br />on the downstream ecosys~em? <br /> <br />a.-17.1. The~e will be no significant =ela~ionshi? be~~een <br />potential dif~erent levels of intake of water for ~he pens~ocks <br />fro~ Lake Powell and the quality of water disc~arged below Glen <br />Canyon Dam and dcwnstream biological productivity. <br /> <br />Justification: The present operation of Glen Canyon Dam ~as <br />the penstock intake below the thermocline in the hypolimnion <br />in Lake Powell. This produces water.~~at is colder than the <br />predam river. The nutrient and sediment levels of this <br />wa-cer is also quite different than predam =iver water. The <br />temperature and levels of nutrien~s in the water discharged <br />below Glen canyon Dam may be directly a:fecting the pri~ary <br />productivity of the system which supports other aquatic <br />organisms. The trout fishery, for example, has apparently <br />been successful because a sufficient food source has been <br />established and the river temperature is near optimum for <br />trout. Other changes in river biota may also be a responSe <br />to the quality of dam discharges. One oitiqation technology <br />~~at might be used to acdress the need to discharge wa~er <br />water is to re~rofit a variable intake structure on Glen <br />Canyon Dam, similar to that at Fla~ing Gorge Dam. The <br />alteration of the quality of the discharge wa~er ~hra~gh ~se <br />of a variable intake s~:::-ucture may cause o~her changes to <br />oc~ur in the ecosystem below the dam. <br /> <br />Information Needs: profiles of Lake Powell water quality <br />(e.g., nutrien~s, sediment, temper3turel need to be taken C~ <br />a regular basis to deter~ine what ~he ?otsntial water <br /> <br />18 <br />