WSPC12525 ‎(2)‎

• File Number: 8220.101.10
• Description: Colorado River Water Projects - Glen Canyon Dam-Lake Powell - Adaptive Management
• State: CO
• Basin: Colorado Mainstem
• Date: 6/2/1998
• Author: DOI-GCMRC
• Title: Assessment of Impacts of Glen Canyon Dam Operations on Water Quality Resources in Lake Powell and the Colorado River in Grand Canyon - Grand Canyon Monitoring and Research Center - Draft - 06-02-98
• Water Supply Pro - Doc Type: Report/Study

OQ2383

Dam, the spillway structures and hollow jet bypass tubes were operated on several occasions. This

allowed significant amounts of water to be released from levels above and below the penstock

zone. These factors combined to cause nearly complete mixing of the reservoir in 1985, due to the

high volume ofreservoir throughput and the operation of the alternative release structures. In the

late 1980's, drought conditions returned to the upper basin and resulted in decreasing reservoir

levels and the return of strong chemical stratification below the penstock level.

1990-1997 The period from 1990 to 1997 was marked by a series of manipulations to the

operation of Glen Canyon Dam for scientific and environmental purposes. Before this time, the .

dam was operated primarily for peaking power generation and water delivery to the Lower Basin

States. In 1990, Phase II of the Glen Canyon Environmental Studies and the development of the

Glen Canyon Dam EIS began. As part of the GCES Phase II Integrated Research Plan (USBR

1990), a series of research flows was initiated from June 1990 to August 1991. These flows ranged

widely in daily fluctuations and ramping rates, interspersed with periods of steady flow. In

November 1991, following the research flow period, the Secretary of the Interior implemented the .

Interim Operation Criteria, which set limits on minimum and maximum discharge, daily range of

discharge, and hourly ramping rates. These criteria remained in place until October 1996, when the

Secretary signed the Record of Decision for the preferred alternative of the Glen Canyon DAM EIS

(U.S. Bureau of Reclamation 1995 and 1996).

Of significance during this latter period was the experimental beachlhabitat building flow in

March and April 1996. This 7-day discharge of 45,000 cfs included a release of 15,000 cfs from the

river outlet works of Glen Canyon Dam. The operation of this structure released water from 100

feet below the penstock withdrawal zone and weakened the strong chemical stratification that had

previously built up below that level.

In February 1997, increases in Upper Colorado River Basin runoff forecasts prompted an
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