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<br />Description of the Preferred Alternative
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<br /> Final EIS on the Operation of Glen Canyon Dam
<br /> Low Volume Months Medium Volume Months High Volume Months
<br />Minimum release (cfs) 8,000 between 7 am and 7 pm 8,000 between 7 am and 7 pm 8,000 between 7 am and 7 pm
<br /> 5,000 between 7 pm and 7 am 5,000 between 7 pm and 7 am 5,000 between 7 pm and 7 am
<br />Habitat maintenance flow Between 30,000 and 33,200 Between 30,000 and 33,200 Between 30,000 and 33,200
<br />(cfs)
<br />Maximum release (cfs) 25,000 (will be exceeded for 25,000 (will be exceeded for 25,000 (will be exceeded for
<br /> habitat maintenance flows) habitat maintenance flows) habitat maintenance flows)
<br />Daily fluctuation 5,000 6,000 8,000
<br />(cfs/24 hrs)
<br />Monthly release volume < 600,000 600,000 to 800,000 > 800,000
<br />(acre-feet)
<br />Ramp rate (cfs/hr) 4,000 up, 1,500 down 4,000 up, 1,500 down 4,000 up, 1,500 down
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<br />Elements common to all alternatives (described in detail in the draft EIS) include:
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<br />Adaptive Management
<br />Flood Frequency Reduction Measures
<br />New Population of Humpback Chub
<br />Emergency Exception Criteria
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<br />Habitat Maintenance Flows, designed to re-form back-
<br />waters and maintain sandbars, will consist of high, steady
<br />releases within the powerplant capacity of 33,200 cfs for 1 or
<br />2 weeks in March, or other months if recommended through
<br />the AMP. These flows have been selected to redistribute
<br />sediment accumulation in pools and backwaters, rebuild
<br />portions of sandbars above the normal peak stage, and
<br />prevent return channels from becoming dominated with
<br />vegetation. Habitat maintenance flows, defined as steady
<br />flows, with minor fluctuations of up to j:,1,000 cfs, would
<br />permit limited voltage regulation within the power grid. The
<br />month of March was selected to allow backwater channels to
<br />re-form prior to the humpback chub spawning period and
<br />because more sediment is likely to be supplied by tributary
<br />flow in March than later in the spring.
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<br />Habitat maintenance flows would not be scheduled when the
<br />projected storage in Lake Powell on January 1 is greater
<br />than 19 million acre-feet (maf). Annual release volumes
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<br />Monitoring and Protecting Cultural Resources
<br />Beach/Habitat-Building Flows
<br />Further Study of Selective Withdrawal
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<br />under such conditions are typically greater than the
<br />minimum annual release volume of 8.23 maf, and such flows
<br />already may be near or exceed powerplant capacity.
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<br />Maintenance flows would begin by increasing flows at a rate
<br />no greater than 4,000 cfs per hour and would conclude by
<br />decreasing flows back to the normal operating range at a
<br />rate no greater than 1,500 cfs per hour. The limit on daily
<br />change in flow would not apply during these transitions.
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<br />Habitat maintenance flows would differ from beach/habitat-
<br />building flows because they would be within powerplant
<br />capacity and would occur nearly every year when the
<br />reservoir is low. Beach/habitat-building flows would be less
<br />frequent. Habitat maintenance flows would not occur in
<br />years when a beach/habitat-building flow is scheduled.
<br />Neither of these special releases would be scheduled in a
<br />year when there is concern for endangered fIsh or other
<br />sensitive resources.
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