Operations * Experimental Releases
Daily high fluctuating releases from Glen Canyon Dam, as part of the Glen Canyon Dam experimental flows, were implemented from January 2, 2005, through April 8, 2005. On Mondays through Saturdays, releases as part of those experimental flows, have ranged between 5,000 cubic feet per second (cfs) and 20,000 cfs. The 20,000 cfs release is being maintained for approximately 11 hours (from 9:00 a.m. until about 8:00 p.m.) and the 5,000 cfs release is being maintained for approximately 6 hours (from 1:00 a.m. until about 7:00 a.m.). The other hours are transitional, where releases will be between the daily high and the daily low. Releases on Sundays have ranged 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. These flows helped keep the non-native fish, especially 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.
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. For additional information on the high-flow experiment, go to: http://137.77.133.1/uc/feature/GCtestflow/index.html
April 8, 2005, is the final day for the experimental high fluctuating releases in 2005. Releases from April 9 through April 30 will be lower than the first three months of 2005. Releases during this period will range from a high of about 9,000 cfs during "on-peak" hours (dawn through early evening hours) to a low of 5,000 cfs during "off-peak" hours (night hours). The total volume of water scheduled to be released in April 2005 is 525,000 acre-feet.
In May 2005, a volume of 605,000 acre-feet is scheduled to be released. This averages out to 10,200 cfs for the month.
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
The Colorado River Basin has now completed 5 consecutive years of severe 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.
Hydrologic conditions have improved over the past 7 months in the Colorado River Basin. Since September 2004, precipitation in the basin has been above average. Snowpack in the basin above Lake Powell is currently 117 percent of average (as of April 6, 2005).
Inflow to Lake Powell, as a percentage of average, has increased since last summer in response to the precipitation events last fall and winter. November 2004 was the first month with above average inflow to Lake Powell since September 1999. Unregulated inflow in January and February was 128 and 118 percent of average, respectively. Unregulated inflow in March was below average, however. Unregulated inflow in March 2005 was 593,000 acre-feet, which is 89 percent of average.
As of April 6, 2005, the elevation of Lake Powell is 3,555.4 feet (144.6 feet from full pool). Current storage is 7.98 million acre-feet (33 percent of live capacity). Lake Powell is now at its low point for the year. The lake level will begin increasing on Saturday, April 9, 2005. Inflow to Lake Powell is currently 8,600 cfs (April 6, 2005) and is increasing.
The National Weather Service (in their April final inflow forecast) is forecasting 8.5 million acre-feet of unregulated inflow to Lake Powell this April through July. This is 107 percent of average. The elevation of Lake Powell is projected to increase from April 9 through mid-July of 2005. Current projections (using the April final inflow forecast) show Lake Powell reaching a peak water surface elevation in July 2005 of about 3,600 feet.
It should be noted, however, that there is uncertainty with these projections. Weather conditions this spring will likely result in shifts to inflow projections for 2005.
Updated April 6, 2005
Tom Ryan