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From: Ronda. Polorson To: Gene J_ Oat.: 12/12197 Time: 9:37:34 AM Page 2 013 .~ Glen Canyon Dam 1998 Annual Plan of Operations prepared in accordance with the Operating Criteria developed for the Grand Canyon Protection Act (GCP A) 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 3695 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 probable 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 water year. With current projected monthly release volumes, hourly powerplant releases likely 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 of20,000 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 Glen Canyon Dam Environmental Impact Statement. With the strong current EI Nino 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 to reduce the risk of uncontrolled spring releases that could result from large forecast errors similar to that which occurred in 1983. Every measure will be taken to prevent such an uncontrolled powerplant bypass this spring in order to protect the Grand Canyon ecosystem downstream of Lake Powell. In this regard, technical discussions have recently occurred regarding the hydrologic triggering mechanisms under which Beach/Habitat Building Flows (BHBF ) could be released from Glen Canyon Dam. The Technical Work Group has evaluated and the Adaptive Management Work Group has recommended the following triggering criteria for the release of a BHBF: