Glen Canyon Dam Operations
In July 2005, a volume of 845,000 acre-feet is scheduled to be released from Lake Powell, which is an average of 13,700 cubic feet per second (cfs). On Mondays through Fridays in July, daily fluctuations due to load following will likely vary between a low of about 9,500 cfs (during late evening and early morning off-peak hours) to a high of about 17,500 cfs (during late afternoon and early evening on-peak hours). On Saturdays and Sundays, releases will likely vary between a low of about 9,500 cfs during off-peak hours to a high of about 16,000 cfs during on-peak hours.
A volume of 872,000 acre-feet is currently scheduled to be released in August. This is an average flow of 14,200 cfs. The exact load-following pattern has not yet been finalized, but releases in August are likely to vary between a low of about 10,000 cfs to a high of about 18,000 cfs. In September, releases will be lower. A total of 500,000 acre-feet is scheduled to be released in September. This is an average flow of 8,400 cfs.
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 has now completed 5 consecutive years of extreme drought. 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 have improved over the past 10 months in the Upper Colorado River Basin. Since September 2004, precipitation in the Upper Basin 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, for instance, 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.
Snowmelt runoff began in April 2005, with inflow to Lake Powell increasing significantly in mid-April. Inflow took another significant jump in the latter half of May 2005, when 2 weeks of hot dry weather triggered a very rapid melt of mid-elevation snow. 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. Snowmelt runoff is now drawing to a conclusion for 2005. Inflow to Lake Powell is currently 22,000 cfs and decreasing.
Total unregulated inflow to Lake Powell in June 2005 was 3,318,000 acre-feet, 108 percent of average. Unregulated inflow to Lake Powell in April and May 2005 was 121 and 128 percent of average, respectively.
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 has been increasing since April 8. As of July 11, 2005, the elevation of Lake Powell is 3,608 feet (92 feet from full pool). Current storage is 12.5 million acre-feet (52 percent of live capacity).
The National Weather Service (in their July inflow forecast) is forecasting 9.1 million acre-feet of unregulated inflow to Lake Powell this April through July. This is 115 percent of average. Unregulated inflow into Lake Powell in water year 2005 is projected to be 110 percent of average.
The elevation of Lake Powell has just about reached its peak for the year. The water surface elevation will likely increase for a few more days perhaps peaking out at elevation 3,609 feet.
Courtesy of Tom Ryan, Bureau of Reclamation