Glen Canyon Dam Releases

Operations * Experimental Releases

Daily high fluctuating releases from Glen Canyon Dam, as part of the Glen Canyon Dam experimental flows, are being implemented from January 2, 2005 through the first week of April 2005. On Mondays through Saturdays, releases will range between 5,000 cubic feet per second (cfs) and 20,000 cfs. The 20,000 cfs release will be maintained for about 11 hours (from 9:00 am until about 8:00 pm) and the 5,000 cfs release will be maintained for about 6 hours (from 1:00 am until about 7:00 am). The other hours are transitional, where releases will be between the daily high and the daily low. Releases on Sundays will range between a low of about 5,000 cfs to a high of about 8,000 cfs.

The January through March high fluctuating releases are intended to benefit the endangered humpback chub. Scientists have recognized that the humpback chub population has been in general decline since high fluctuating flows were curtailed in November of 1991. Those flows helped keep the non-native fish, especially the rainbow and brown trout, in check. The trout are thought to prey upon and compete with native fish such as the endangered humpback chub. This is the third consecutive year of high fluctuating winter releases as part of the experimental flows.

Monthly release volumes in January, February, and March 2005 are scheduled to be 779,000, 723,000, and 807,000 acre-feet, respectively, which averages out to about 14,000 cfs per day on Mondays through Saturdays and 6,700 cfs per day on Sundays. On April 8, 2005 high fluctuating releases are scheduled to end.

On November 21, 2004, releases from Glen Canyon Dam were increased for a high-flow experiment. Releases were increased to 41,000 cfs, with this release level maintained for 60 hours. Further information on the high-flow experiment can be found at:

Because of the draw down condition of Lake Powell, releases from Lake Powell in water year 2005 are being scheduled to meet the minimum release objective of 8.23 million acre-feet. Experimental releases will not change the total volume of water to be released from Lake Powell in water year 2005.

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 water years. 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 2004 in the Colorado River Basin with a period of three consecutive months of above average precipitation. Basinwide precipitation in September, October and November was 165, 155 and 135 percent of average, respectively. Unfortunately, December has lacked the storms of the three preceding months and will likely end up as a month with below average precipitation. Basinwide snowpack is above average, however. As of December 30, 2004, basinwide snowpack in the Colorado River Basin is 106 percent of average.

Unregulated inflow to Lake Powell in November was 558,000 acre-feet, or 102 percent of average. This was the first month with above average inflow to Lake Powell since September 1999. Inflow, as a percentage of average, has been increasing since the summer in response to the precipitation events this fall. Unregulated inflow was extremely low this past summer (only 35 and 29 percent of average in July and August, respectively), but increased to 68 percent of average in September and 92 percent of average in October. Unregulated inflow in December will likely be about 85 percent of average. The National Weather Service issued an April through July inflow forecast for Lake Powell in mid-December. This forecast is for 7.3 million acre-feet of unregulated inflow (92 percent of average) to Lake Powell in April through July of 2005.

The fall precipitation 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. However, drought conditions continue to prevail in the Colorado River Basin. To "break" the drought will require a pattern of above-average precipitation through the winter and into next spring.

Low inflows over the past 5 years have reduced water storage in Lake Powell. As of December 29, 2004, the elevation of Lake Powell is 3,564.5 feet (135.5 feet from full pool). Current storage is 8.7 million acre-feet (36 percent of live capacity). As of December 28, 2004, observed inflow to Lake Powell was 7,700 cfs, about 86 percent of what is normally seen in late December.

Under the current inflow forecast, and in combination with scheduled releases, the water surface elevation of Lake Powell is projected to decline until April. The current projections show the lake decreasing to an elevation of about 3,551 feet in early April. The elevation of Lake Powell is projected to increase from April through mid-July of 2005. Current projections show Lake Powell reaching peak in July 2005 of about 3,585 feet. It should be noted, however, there is considerable uncertainty with these projection. Weather conditions this winter and next spring will ultimately determine how much runoff there will be into Lake Powell in 2005.

Updated December 30, 2004

This release courtesy Tom Ryan, US Bureau of Reclamation