WSP08901

• File Number: 8220.101.09
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 10/13/1993
• Author: USDOI-USFWS
• Title: Draft Biological Opinion-Operation of Glen Canyon Dam as the Modified Low Fluctuating Flow Alternative of the Draft Envronmental Impact Statement Operation of Glen Canyon Dam
• Water Supply Pro - Doc Type: Biological Opinion

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Tobie I. Moo;fIed Low Fl":" Flow A1_0~ (^"'''''''' Om, EIS "" """0.. of
Glen Canyon Dam, July 1993)
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Minimum Habitat Maximum Daily Monthly Ramp
release Maint. Flc II release Fluctuation release vol rate
(cfs) 1 (cfs) (cfs) (cfs/24 hr) (acre-feet) ( cfs/hr)
8,000 33,200 20,000 5,000 <600,000 2,500 up
between Exceeded 1,500 down
7am & 7pm during hab.
5,000 night maint flows
same same same 6,000 600,000 to same
800,000
same same same 8,000 > 800,000 same

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Described in February 25, 1993 memorandum from Lee McQuivey, Bureau of
Reciamation, Salt Lake City, Utah.

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Habitat maintenance flows are defined as high, steady releases within powerplant capacity
(33,200 cfs maximum) for 7 to 14 days in March Ot April. Other months could be considered
under the Adaptive Management Program. Habitat maintenance flows would occur every year
in which the projected storage of Lake Powell is less than 19 mat (low reservoir condition) on
January 1. They would not occur when beach and habitat building flows are scheduled, Beach
and habitat building flows would be of greater magnitude (40,000 to 45,000 cfs) and occur less
frequently, I in 5 years when Lake Powell is low (60% of time), for an occurrence in all years
of 1 in 8 years or 12 % (Tim Randle, personal communication). Neither maintenance nor
building flows would occur in a year when there is special concern for a sensitive resource, for
example, a good year class of humpback chub in the upper reaches of the mainstem.
Adaptive Management Program would coordinate such recommendations.

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Figure 2 shows a plot of monthly releases for the proposed action. The maximum habitat
maintenance flow is included in April. U,,) W .<0

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t3 October 1993 Draft biological opinion 2-21,93-F-t67

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