Glen Canyon Dam Update

Drought conditions persist in the Colorado River Basin. Conditions were somewhat better in February with basinwide precipitation at about 115 percent of average. December, 2002 and January, 2003 were very dry months, however. Basinwide precipitation in December and January was only 60 and 35 percent of average, respectively. Upper Colorado River basin snowpack is currently 82 percent of average (as of March 5, 2003) The March final inflow forecast issued by the National Weather Service is calling for 4.8 million acre-feet of unregulated runoff into Lake Powell during the 2003 April through July time period. This is 61 percent of average.

Inflow to Lake Powell continues to be significantly below average. Unregulated inflow into Lake Powell in October, November, December and January was 56, 69, 57 and 58 percent of average, respectively. Unregulated inflow in February, 2003 was 263,000 acre-feet, only 62 percent of average.

Drier than average conditions have now prevailed for the past three years in the Colorado River Basin. Total unregulated inflow into Lake Powell in water year 2000 and 2001 was 62 and 59 percent of average, respectively, and only 25 percent of average in 2002. Inflow in 2002 was the lowest ever observed since the completion of Glen Canyon Dam in 1963. These low inflows have reduced water storage in Lake Powell. The current elevation of Lake Powell is 3,610.4 feet (89.6 feet from full pool). Current storage is approximately 12.8 million acre-feet (52 percent of capacity). The water surface elevation of Lake Powell will likely continue to decline through March and into the early part of April. The current projection shows that the water surface elevation of Lake Powell will reach a low in 2003 of about 3,606 feet (94 feet below full pool) in April 2003.

Experimental releases from Glen Canyon Dam began on January 1, 2003. Daily high fluctuating releases from Glen Canyon Dam are being implemented from January through March 2003 to reduce spawning and recruitment of non-native fish. Releases will range between a high of 20,000 cubic feet per second (cfs) to a low of 5,000 cfs each day. The 20,000 cfs releases will be maintained for approximately 9 hours each day (from about 11:00 a.m. to about 8:00 p.m.), while the 5,000 cfs releases will be maintained for approximately 8 hours each day (from about 1:00 a.m. to about 9:00 a.m.). The remainder of the hours will be transition releases where releases are between the daily high and the daily low. This pattern will be maintained for 7 days a week during the January through March time period. It should be noted that due to real-time power generation considerations and regulation to stabilize the power system, actual releases may deviate somewhat from this pattern. It is also possible that during the month of March, there may be a few days, where the pattern will be adjusted by one hour, where the period of off-peak releases (5000 cfs) would end at 8:00 a.m. instead of 9:00 am.

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 highly 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.

The high fluctuating releases will continue through March 2003. The monthly release volume from Glen Canyon Dam in March is 788,000 acre-feet, which averages out to 12,800 cfs per day. High fluctuating releases end in April, 2003. A total of 600,000 acre-feet is currently scheduled for release in April, 2003. This is an average of 10,000 cfs. The fluctuation range in April, 2003 will likely vary from a low of about 7,000 cfs to a high of about 13,000 cfs.

The experimental releases from Glen Canyon Dam received environmental clearances in December 2002. The flows were analyzed in an environmental assessment in accordance with the National Environmental Policy Act. The experimental flows are the result of ongoing studies by scientists from the United States Geological Survey and were recommended by the Glen Canyon Dam Adaptive Management Work Group, a federal advisory committee. The experimental releases address the decline of two key resources in the Grand Canyon: sediment and population viability of endangered humpback chub. The Finding of No Significant Impact on the experimental releases can be found at

Because of the draw down condition of Lake Powell, releases from Lake Powell in water year 2003 are being scheduled to meet the minimum objective release of 8.23 million acre-feet. This is consistent with the requirements of the 1970 Criteria for Coordinated Long-Range Operation of Colorado River Reservoirs.

This release courtesy Tom Ryan