Glen Canyon Dam Update

Glen Canyon Dam Operations

Beginning September 3, 2005 and continuing through October 31, 2005 a test release will take place from Glen Canyon Dam. This test release is being implemented to analyze the effects of two flow regimes (steady and limited fluctuating flows) on endangered humpback chub habitats and on conservation of fine sediment in the river corridor below Glen Canyon Dam.

On September 3, 2005, the fluctuation range in Glen Canyon Dam releases will be limited to a low of 6,500 cubic feet per second (cfs) ranging to a high of 9,000 cfs. This flow regime will continue through September 20, 2005. Beginning on September 21, 2005 and continuing through October 7, 2005, scheduled releases will be steady at 8,000 cfs. From October 8, 2005 through October 19, 2005, releases will return to the 6,500 to 9,000 cfs fluctuating flow regime. Finally, from October 20,

2005 through October 31, 2005 scheduled releases will return to the steady 8,000 cfs regime. Normal operations will resume on November 1, 2005.

Releases will transition to the lower regime as we move from August into September. Releases on August 30, August 31, September 1, and September 2 will average about 15,000 cfs, 13,000 cfs, 12,250 cfs and 10,600 cfs, respectively.

The release volume in both September and October 2005 will be 497,000 acre-feet. Because of the draw down condition of Lake Powell, releases from Lake Powell in water year 2005 are being scheduled to meet the release objective of 8.23 million acre-feet.

Upper Colorado River Basin Hydrology

The Colorado River Basin experienced 5 consecutive years of extreme drought from September 1999 through September 2004. In the summer of 1999, Lake Powell was essentially full with reservoir storage at 97 percent of capacity. Inflow volumes for 5 consecutive water years were significantly below average. Total unregulated inflow in water years 2000, 2001, 2002, 2003, and 2004 was 62, 59, 25, 51, 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 improved in water year 2005 in the Upper Colorado River Basin. Precipitation in the Upper Basin in water year 2005 has been above average. Rains in the fall of 2004 helped reduce soil moisture deficits caused by the drought. River flows responded to the fall rains with increased flows. November 2004 was the first month with above average inflow to Lake Powell since September of 1999. Snowpack in the Upper Colorado River Basin ranged from average to moderately above average throughout the winter of 2004-2005.

April through July is the snowmelt runoff period in the Colorado River Basin. April through July unregulated inflow to Lake Powell was 8.81 million acre-feet in 2005. This is 111 percent of average. Unregulated inflow to Lake Powell in water year 2005 (October 2004 through September 2005) is projected to be 107 percent of average.

Inflow to Lake Powell reached a peak of 77,000 cfs on May 28, 2005.

Peak inflow to Lake Powell had not been this high since 1997. Since early July, inflow to Lake Powell has been below average. Unregulated inflow to Lake Powell in July was 91 percent of average. August unregulated inflow is expected to be about 75 percent of average.

Observed inflow to Lake Powell on August 28, 2005 is 7,000 cfs.

Lake Powell reached a low elevation on April 8, 2005, at 3,555 feet (145 feet from full pool). Reservoir storage had declined to 33 percent of live capacity. The last time Lake Powell had been this low was in May 1969. The water surface elevation increased through the spring and early summer, reaching a peak elevation of 3,608.4 feet on July 14, 2005. The current elevation of Lake Powell is 3,603.3 feet (96.7 feet from full pool). Current storage is 12.1 million acre-feet (50 percent of live capacity).

The water surface elevation of Lake Powell will likely continue to decrease through the fall and winter until April 2006, when anticipated snowmelt runoff will cause the water surface level to increase once more. The projected elevation of Lake Powell on January 1, 2006 is about 3,600 feet.

Updated August 29, 2005

Tom Ryan