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Glen Canyon Dam Record of Decision and Operating Constraints

The Glen Canyon Dam EIS process was completed with the issuance of a Record of Decision on October 9, 1996, signed by Secretary of the Interior Bruce Babbitt. The Record of Decision affirmed the selection of the preferred alternative, which was the Modified Low Fluctuating Flow Alternative, for operating Glen Canyon Dam. Reclamation issued the Operating Criteria for Glen Canyon Dam early in 1997. The 1997 Operating Criteria expanded on the operational criteria contained in the EIS and ROD, and provided Western and Reclamation Operations staffs with the guidance they need to operate the Dam and the SLCA/IP power system.

The Operating Criteria limits the dam's up- and downramp release rates. For example, the maximum allowable release from Glen Canyon Dam is set at 25,000 cubic feet of water per second (cfs) (or about 1,000 MW). The criteria include exceptions to the maximum release for Beach/Habitat Building Flows and Habitat Maintenance Flows such as occurred in March 1996, and releases to avoid spills or floodflow release during high runoff years. Minimum releases are 8,000 cfs (320 MW) between the peak hours of 7:00 a.m. to 7:00 p.m., and 5,000 cfs (200 MW) at night.

The Operating Criteria also sets limits on the allowable release fluctuations in any 24-hour period. The amounts vary depending on the amount of water scheduled to be released in a given month. For example, the allowable daily fluctuation is 5,000 cfs/24 hours for months in which scheduled water releases through the dam are less than 600,000 acre feet (af) during the month. Fluctuations will be held at 6,000 cfs/24 hours for months of scheduled releases between 600,000 and 800,000 af, and at 8,000 cfs/24 hours for months of scheduled releases greater than 800,000 af/month.

Finally, the Operating Criteria also limits the rate at which the generators may ramp up or down. The maximum powerplant ramp rates are set at 4,000 cfs (160 MW) per hour increasing and 1,500 cfs (75 MW) per hour decreasing. Exceptions to the operating constraints are allowed in emergencies including: insufficient generating capacity, transmission system overload, voltage and frequency control, system restoration, and humanitarian reasons. The frequency of unanticipated flood flows will be reduced initially through the Annual Operating Plan process and eventually by raising the spillway gates by 4.5 feet.

In March and April 1996, Reclamation conducted a Beach/Habitat Building release which gained international attention. These kinds of Beach/Habitat Building and Habitat Maintenance Flows are also included in the Operating Criteria. The Beach/Habitat Building Flows consist of up to 14 days of flows not to exceed 45,000 cfs. They will be accomplished by using reservoir releases greater than powerplant capacity required for dam safety purposes. Habitat Maintenance Flows consist of up to 14 days of flow not to exceed powerplant capacity (33,200 cfs) during March. Typically these flows will occur when annual releases are at or near the minimum objective release of 8,230,000 af.

The CRSP MC in collaboration with other Western offices, SLCA/IP firm power customers, Federal agencies, environmental groups, and other interested parties continues to be fully involved in all the issues surrounding Glen Canyon Dam. The CRSP MC currently participates and represents Western in several Glen Canyon Dam related groups including the Management Objectives Subgroup, the Research Center Coordination Group, the Technical Workgroup (TWG), and the Adaptive Management Workgroup (AMWG).

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