WSP03790

• File Number: 8220.101.13
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 10/1/1998
• Author: Secretary of Inter
• Title: Report to Congress: Operations of the Glen canyon Dam Pursuant to the Grand Canyon Protection Act of 1992 ‎(Water Years 1997 and 1998)‎
• Water Supply Pro - Doc Type: Annual Report

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APPENDIX C

GLEN CANYON DAM 1998 ANNUAL PLAN OF OPERATIONS
PREPARED IN ACCORDANCE WITH THE OPERATING CRITERIA
DEVELOPED FOR THE GRAND CANYON PROTECTION ACT

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This plan is prepared in conformance with section 1804(c)(I)(A) of the GCPA. Any changes
to the plan would require reconsultation in accordance with this Act.

In water year 1997, Glen Canyon Dam was operated in accordance with the criteria
established in response to the 1992 Grand Canyon Protection Act, including the constraints
on daily fluctuations and ramping rates, Since the annual release volume was 13.8 maf,
powerplant releases were above normal for much of the year. In portions of February, March,
June, and July, average daily releases were 27,000 cfs, and thus were released at a steady
flow rate. Lake Powell's peak elevation for the year was 3,695 feet and no water bypassed
the powerplant.

As a result of the preparation of the Annual Operating Plan under the 1968 Colorado River
Basin Project Act, monthly release volumes from Glen Canyon Dam during 1998 are
expected to range from 600,000 af to 1,200,000 af, Under the most probably inflow
conditions in water year 1998, Glen Canyon Dam is expected to release about 10.75 maf
through the Grand Canyon to Lake Mead. This is about 2.5 maf greater than the minimum
objective release and is the result of high reservoir storage in both Lakes Powell and Mead.
Lake Powell is expected to fill in July, Monthly updates to these release projections will be
made throughout the year.

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With current projected monthly release volumes, hourly powerplant releases will exceed
20,000 cfs from October through the month of January and again during the summer peak
months of July and August, when monthly release volumes are at their highest for the year.
Average daily releases of 20,000 cfs are expected during these months. If average daily
releases above 25,000 cfs are made, they will be made as steady flows. Projected daily
allowable fluctuations therefore will be between 6,000 cfs and 8,000 cfs (see criteria).
Minimum releases of 5,000 cfs at night and 8,000 cfs during the day and ramping rates of
4,000 cfslhr increasing and 1,500 cfslhr decreasing will be followed, All of the above is
outlined in the Record of Decision implementing the preferred alternative of the GCDEIS.

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With the strong current El Niiio Southern Oscillation anomaly, there is some indication that
winter precipitation could be higher than normal in the southern portion of the Upper
Colorado River Basin, and that spring precipitation could also be higher than normal in the
northern portion of the Basin. Since there are concerns for resulting unplanned spills from
Glen Canyon Dam, releases from Glen Canyon Dam are expected to be higher than normal
during the fall months in order to achieve a prudent January 1, 1998, reservoir storage level.
Releases throughout the year will be made in such a way so as to reduce the risk of
uncontrolled spring releases that could result from large forecast errOrs similar to that which
occurred in 1983. '