Experimental releases from Glen Canyon Dam have received environmental clearances and are set to begin January 1, 2003. The flows were analyzed in an environmental assessment in accordance with the National Environmental Policy Act. The proposed flows are the result of ongoing studies by scientists from 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 EA can be found at: http://www.uc.usbr.gov/envdocs/ea/gc/gc_release.html
As part of the experiment, daily high fluctuating releases from Glen Canyon Dam will be implemented from January through March 2003, beginning January 1, 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 about 9 hours each day (from about 11:00 am until about 8:00 pm), while the 5,000 cfs releases will be maintained for about 8 hours (from about 1:00 am until about 9:00 am). 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.
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 a 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.
Monthly release volumes in January, February, and March 2003 will be 788, 712, and 788 thousand acre-feet, respectively, which averages out to 12,800 cfs per day.
Drought conditions persist in the Colorado River Basin. The basin received some drought relief during the months of September and October, with basinwide precipitation in those months being 185 and 110 percent of average, respectively. While there was some precipitation in early November, there has been essentially no precipitation in the basin since November 11, 2002. Snowpack in the Colorado River Basin is 79 percent of average as of December 13, 2002. The National Weather Service has issued its first water supply forecast for next spring's runoff. This forecast is calling for 5.7 million acre-feet of unregulated runoff into Lake Powell during the 2003 April through July time period. This is 72 percent of average.
Inflow to Lake Powell continues to be significantly below average. Unregulated inflow into Lake Powell in September and October 2002 was 58 and 56 percent of average, respectively. Inflow in November 2002 was 377,000 acre-feet, or 69 percent of average. Inflow to Lake Powell is expected to remain below average through the winter and early spring.
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 3,622.0 feet (78.0 feet from full pool). Current storage is approximately 14.0 million acre-feet (57 percent of capacity). The water surface elevation of Lake Powell will likely continue to decline for the remainder of this year into the early spring of 2003. The current projection shows that the water surface elevation of Lake Powell will reach a low of about 3,610 feet (90 feet below full pool) in April 2003, when next spring's runoff begins.
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.