8128

• UCREFRP Catalog Number: 8128
• Author: U.S. Bureau of Reclamation.
• Title: Operation of Glen Canyon Dam\
• USFW Year: 1995.
• Copyright Material: NO

Description of Alternatives
across and within the hour. In some cases, dispatcher experience may be a
factor. For a number of reasons (typically for meeting monthly release
volumes), minimum flows are frequently above the objective minimum.
Occasionally, power system emergencies prevent meeting the minimum
release objectives.
Maximum Flow. Maximum flows are determined by powerplant
capacity, the power demand at the time of release, and the amount of
water required and/or available for release in a given month. As much as
33,200 cfs can be discharged through the powerplant if the reservoir is at
the appropriate elevation. Flows greater than 33,200 cfs are discharged
through the outlet works first and then through the spillways. Peak
discharges under normal no action operations do not exceed 31,500 cfs.
Releases greater than 31,500 cfs are steady on a daily basis.
Range of Fluctuating Flows. The range of daily fluctuations under the
No Action Alternative is only restricted to between the minimum and
maximum flows. However, power considerations often considerably
restrict the actual range of fluctuations.
Ramp Rate. The ramp rate is the rate of change in discharge to meet the
electrical load by achieving either higher or lower releases. North
American Electric Reliability Council operating criteria require Western to
meet scheduled load changes by ramping up or down beginning at
10 minutes before the hour and ending at 10 minutes after the hour. Any
ramping to meet scheduled load changes occurs during that same
20-minute period. The principal times of change are in the morning, when
releases are increased to respond to the peak daytime demand, and at
night, when releases are decreased as the electrical demand diminishes. A
computerized automatic generation control (AGC) system controls the
rate of release and generation on an instantaneous basis.
Under historical operations, scheduled ramping typically has resulted in
large river stage changes. However, the continuous small changes in
discharge caused by AGC rarely affect river stage by more than a foot.
Under the No Action Alternative, the only restriction on ramp rates is the
physical capability of the generators. The 1-hour up ramp rates have been
less than 4,000 cfs per hour about 32 percent of the time and greater than
8,000 cfs about 11 percent of the time. The down ramp rates have been less
than 4,000 cfs about 29 percent of the time and greater than 8,000 cfs about
7 percent of the time.
20 Glen Canyon Dam EIS Summary