November 2004. Releases from Glen Canyon Dam in December will average about 9,800 cubic feet per second (cfs) with a total of 600,000 acre-feet scheduled to be released. The hourly release pattern has not been finalized, but it is expected that daily fluctuations due to load following will likely vary between a low of about 6,000 cfs (during late evening and early morning off-peak hours) to a high of about 12,000 cfs (during late afternoon and early evening on-peak hours). On Saturdays and Sundays, on-peak releases will likely be somewhat below the 12,000 cfs level.
Upper Colorado River Basin Hydrology
Water year 2005 began on October 1, 2004. The Colorado River Basin has now completed 5 consecutive years of drought. In the summer of 1999 Lake Powell was essentially full, with reservoir storage at 97 percent of capacity.
Since that time, inflow volumes have been below average for 5 consecutive years. The last month when inflow to Lake Powell was above average was September 1999. Total unregulated inflow to Lake Powell in water year 2004 was only 51 percent of average. Unregulated inflow in water years 2000, 2001, 2002, and 2003 was 62, 59, 25, and 51 percent of average, respectively. Inflow in water year 2002 was the lowest ever observed since the completion of Glen Canyon Dam in 1963.
A favorable trend emerged in September and October, 2004 in the Colorado River Basin. Precipitation in both months was significantly above average. Basinwide precipitation in September was 165 percent of average, with October precipitation at 155 percent of average. However, thus far, November precipitation throughout the Colorado River Basin has been below average. Basinwide snowpack in the Colorado River Basin is currently (as of November 20, 2004) 109 percent of average.
Inflow to Lake Powell, which was extremely low this past summer (only 35 and 29 percent of average in July and August, respectively), has picked up in response to the precipitation events in September and October. Unregulated inflow to Lake Powell in September was 68 percent of average and 92 percent of average in October. November unregulated inflow will likely end up being very close to average. The fall precipitation has improved soil moisture conditions in the basin. This will favor a more efficient runoff next spring with more snowmelt going to the rivers instead of into the soils as has been the case the past few years. Drought conditions continue to prevail in the Colorado River Basin, however. To "break" the drought will require a pattern of above-average precipitation through the winter and into next spring. Water year 2005 is off to a good start, but it is too early to celebrate.
As of November 19, 2004, observed inflow to Lake Powell is 7,600 cfs, 80 percent of what is normally seen in late-November. Low inflows over the past 5 years have reduced water storage in Lake Powell. As of November 19, 2004, the current elevation of Lake Powell is 3,570.6 feet (129.4 feet from full pool). Current storage is 9.2 million acre-feet (38 percent of live capacity).
Under the current inflow forecast in combination with scheduled releases, the water surface elevation of Lake Powell is projected to decline the remainder of the year, with current projections showing the lake reaching an elevation of about 3,564 feet on January 1, 2005. This projection factors in releases made under the high-flow experiment.
Operations * High-Flow Experiment
Beginning on Sunday November 21, 2004 releases from Glen Canyon Dam will be increased for a high-flow experiment. Releases will be increased to power plant capacity of 26,000 cubic feet per second (cfs) the morning of November 21. At 7:00 am on November 21 releases greater than powerplant capacity will begin through use of the river bypass tubes. Releases from the bypass tubes will be increased incrementally for 21 hours until the four river bypass tubes are operating at a combined capacity of 15,000 cfs. At this time (November 22 at 4:00 am) the total release from Glen Canyon Dam will be approximately 41,000 cfs. The 41,000 cfs release will be maintained for 60 hours. Releases will then be reduced by 1,500 cfs per hour until a release of 8,000 cfs is achieved (This will occur at 1:00 pm on Thanksgiving Day).
Releases will then remain constant at 8,000 cfs for the remainder of November to facilitate further data collection and monitoring of the Grand Canyon by scientists from the Grand Canyon Monitoring and Research Center and other agencies.
The high-flow experiment will not alter the total volume of water released from Lake Powell in water year 2005. The 2005 Colorado River Annual Operating Plans calls for an annual release of 8.23 million acre-feet from Lake Powell in water year 2005. Monthly release volumes from Glen Canyon Dam will be adjusted downward over the course of the next 8 months such that the elevation of Lake Powell in the summer of 2005 will be the same, regardless of whether the high flow experiment had taken place.
Additional information on the high-flow experiment can be found at
http://www.usbr.gov/newsroom/newsrelease/detail.cfm?RecordID=3001
This release courtesy of Tom Ryan