Glen Canyon Dam Operations
In June 2005, a volume of 800,000 acre-feet is scheduled to be released from Lake Powell, which is an average of 13,400 cubic feet per second (cfs). On Mondays through Fridays in June, daily fluctuations due to load following will likely vary between a low of about 9,000 cfs (during late evening and early morning off-peak hours) to a high of about 17,000 cfs (during late afternoon and early evening on-peak hours). On Saturdays and Sundays, releases will likely vary between a low of about 9,000 cfs during off-peak hours to a high of about 15,500 cfs during on-peak hours.
A volume of 845,000 acre-feet is currently scheduled to be released in July. This is an average flow of 13,700 cfs. The exact load-following pattern has not yet been finalized, but releases in July are likely to vary between a low of about 9,300 cfs to a high of about 17,300 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. 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 9 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. Cooler and wetter than average weather conditions prevailed in the basin in the latter part of April and the first part of May. This weather pattern delayed the snowmelt somewhat, and also added additional mountain snow at higher elevations.
The latter half of May 2005 feature hot dry conditions, which triggered a very rapid melt of snow in the Colorado River Basin. Some streamflow gages in the Upper Colorado River Basin broke records for late May daily flows (San Juan River at Carracas, Colorado and Duchesne River near Randlett, Utah to name a couple). Inflow to Lake Powell reached a peak of 77,000 cfs on May 28, 2005. Peak inflow to Lake Powell has not been this high since 1997. Cooler temperatures moved into the basin at the end of May and have persisted into early June. River flows have fallen off from the high flows seen in late May. Inflow to Lake Powell is currently 62,000 cfs (June 3, 2005) and is decreasing.
Total unregulated inflow to Lake Powell in April 2005 was 1,188,000 acre-feet, which is 121 percent of average. Unregulated inflow to Lake Powell in May 2005 was 2,893,000 acre-feet, 128 percent of average.
Lake Powell reached a low elevation on April 8, 2005, at 3,555.1 feet (144.9 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 June 3, 2005, the elevation of Lake Powell is 3,589 feet (111 feet from full pool). Lake Powell is currently rising by almost one foot per day (although this rate will decrease to about a half a foot per day by mid-June). Current storage is 10.7 million acre-feet (44 percent of live capacity).
The National Weather Service (in their June final inflow forecast) is forecasting 9.0 million acre-feet of unregulated inflow to Lake Powell this April through July. This is 113 percent of average. Unregulated inflow in June is projected to be 3,200,000 acre-feet. The elevation of Lake Powell is projected to increase through mid-July of 2005. Current projections (using the June final inflow forecast) show Lake Powell reaching a peak water surface elevation in mid-July 2005 of about 3,607 feet. At this elevation, Lake Powell storage will be about 51 percent of capacity. It should be noted, however, that there still remains some uncertainty with these projections.
This release courtesy Tom Ryan, US Bureau of Reclamation