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Last modified
7/14/2009 5:02:30 PM
Creation date
5/20/2009 10:43:33 AM
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UCREFRP
UCREFRP Catalog Number
7387
Author
U.S. Bureau of Reclamation.
Title
Glen Canyon Environmental Studies Executive Summaries of Technical Reports.
USFW Year
1988.
USFW - Doc Type
\
Copyright Material
NO
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<br />8 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />releases. The stable beach area that develops in <br />response to fluctuating flows is smaller than that <br />developed during steady flows of the same annual <br />volume, and could be substantially smaller depending <br />upon release patterns. <br /> <br />MODIFIED OPERATIONS COULD PROTECT OR ENHANCE MOST <br />RESOURCES. The GCES found that changes in operation of <br />the dam to reduce fluctuations and avoid flood releases <br />could reduce the resource losses occurring under <br />current operations and, in some cases, even improve the <br />status of the resources. Five modified patterns of <br />operations were designed, each to address one or more <br />critical resources. These patterns have been <br />constrained only by the need to release a minimum of <br />8.23 million acre feet (maf) per year, maintain minimum <br />flows of 1,000 cfs in winter and 3,000 cfs in summer, <br />and stay within the designated powerplant capacity of <br />31,500 cfs. These modifications only approximate ideal <br />release patterns for individual downstream resources. <br />They illustrate the types of changes that would protect <br />or enhance resources, but do not represent the full <br />range of possible options. These modifications should <br />not be considered as fullY developed or recommended <br />operational schemes. <br /> <br />CONCLUSIONS <br /> <br />OUR UNDERSTANDING OF THE RELATIONSHIPS BETWEEN DAM <br />OPERATIONS AND DOWNSTREAM RESOURCES IS NOT COMPLETE. <br />The limited time available for the Glen Canyon <br />Environmental Studies increases the uncertainty of <br />long-term predictions made from data collected during <br />the study. The coincidence of the GCES with high flows <br />that were not typical of pre-1983 releases limited our <br />ability to determine the response of resources to low <br />and fluctuating flows. These high releases required <br />major changes in research design as the studies were <br />in progress. We believe, however, that the more <br />general conclusions that dam operations affect <br />downstream resources and that modified operations <br />would better protect these resources, would not change <br />due to these uncertainties. <br /> <br />Nowhere were time and flow limitations more strongly <br />felt than in determining the effects of dam operations <br />on the humpback chub. The legal and biological status <br />of this species makes decisions based on inadequate or <br />incomplete information particularly dangerous. In this <br />respect, 'we have erred on the side of caution and wish <br />to reemphasize the need for further studies with <br />
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