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Description of Alternatives <br />and is the warmest possible temperature (not necessarily the optimum <br />temperature) for native fish or other resources. Withdrawal levels could be <br />seasonally adjusted to meet ecological objectives, although this would <br />involve complex factors. <br />Releasing warmer water during the spring and summer months could <br />possibly raise river temperatures in some downstream reaches to a level <br />that would support spawning by humpback chub and other native fish. <br />However, increasing the temperature of river water may also create <br />problems for species currently inhabiting the Colorado River below Glen <br />Canyon Dam. The cold river temperatures may act as a barrier to the <br />establishment of non-native predatory fish from Lake Mead. Higher water <br />temperatures may encourage the upstream migration and establishment of <br />predatory fish, further endangering humpback chub and other native fish <br />through increased predation or competition from non-native migrants and <br />resident non-native fish. <br />The cost of installing multilevel intake structures at Glen Canyon Dam has <br />been estimated at $60 million. This estimate is based on actual costs for <br />similar structures at Flaming Gorge Dam. <br />Reclamation would implement a selective withdrawal program and <br />determine feasibility by aggressively pursuing and supporting research on <br />the effects of multilevel intake structures at Glen Canyon Dam and would <br />use the research results to make a firm decision on construction. FWS, in <br />consultation with AGFD, would be responsible for recommending to <br />Reclamation whether or not selective withdrawal should be implemented <br />at Glen Canyon Dam. Reclamation would be responsible for design, <br />NEPA compliance, permits, construction, operation, and maintenance. <br />Emergency Exception Criteria <br />Normal operations described under any alternative would be altered <br />temporarily to respond to emergencies. These changes in operations <br />would be of short duration (usually less than 4 hours) and would be the <br />result of emergencies at the dam, downstream, or within the intercon- <br />nected electrical system. Examples of system emergencies include: <br />• Insufficient generating capacity <br />• Transmission system: overload, voltage control, and frequency <br />• System restoration <br />• Humanitarian situations (search and rescue) <br />16 Glen Canyon Dam EIS Summary