In August 2004, a volume of 900,000 acre-feet is scheduled to be released from Lake Powell, which is an average of 14,600 cubic feet per second (cfs). On Mondays through Fridays in August, daily fluctuations due to load following will likely vary between a low of about 10,000 cfs (during late evening and early morning off-peak hours) to a high of about 18,000 cfs (during late afternoon and early evening on-peak hours). On Saturdays, releases will likely vary between a low of about 10,000 cfs during off-peak hours to a high of about 16,500 cfs during on-peak hours. On Sundays, releases will likely vary between a low of about 10,000 cfs during off-peak hours to a high of about 17,000 cfs during on-peak hours. The release pattern in August will be similar to that observed in July. Releases in September, 2004 will be much lower. A volume of 480,000 acre-feet is scheduled to be released in September, which is an average of 8,000 cfs.
Because of the draw down condition of Lake Powell, releases from Lake Powell in water year 2004 are being scheduled to meet the minimum release objective of 8.23 million acre-feet. This is consistent with the requirements of the Criteria for Coordinated Long-Range Operation of Colorado River Reservoirs.
Upper Colorado River Basin Hydrology
The summer season in the Colorado River Basin has featured cooler than average temperatures with precipitation at near average levels. This has caused inflows to be just a bit above those forecasted when the summer began. Regardless, inflows remain much below average. In early June, April through July unregulated inflow to Lake Powell was forecasted to be 43 percent of average. Actual April through July unregulated inflow in 2004 will likely end up being 3.64 million acre-feet, 46 percent of average.
The month of March dashed hopes that 2004 would bring relief to the ongoing drought in the Colorado River Basin. Basin snowpack on March 1, 2004 was 96 percent of average. At that time, the April through July inflow was forecasted to be 82 percent of average. The weather pattern in March, 2004 was very dry and extremely warm for early spring. Temperatures around the basin for much of the month were 20 degrees above average. Basinwide snowpack dropped over 30 percentage points in March. Inflow projections to Lake Powell were reduced to 50 percent of average in early April.
The Colorado River Basin is completing its 5th year of drought. In July 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 years. The last month when inflow to Lake Powell was above average was September 1999. Unregulated inflow in water years 2000, 2001, 2002, and 2003 was 62, 59, 25, and 51 percent of average, respectively. Total unregulated inflow for water year 2004 is now forecasted to be 52 percent of average. Inflow in water year 2002 was the lowest ever observed since the completion of Glen Canyon Dam in 1963.
Peak inflow to Lake Powell this year occurred on May 14 (about three weeks earlier than normal) when inflow was 21,400 cfs. As of July 29, 2004 observed inflow to Lake Powell was 6,900 cfs about 51 percent of what is normally seen as July comes to a close. Total unregulated inflow to Lake Powell in March, April, May, and June of this year was 81, 83, 51, and 36 percent of average, respectively. Unregulated inflow in July will likely be 550,000 acre-feet, or 35 percent of average.
Low inflows the past 5 years have reduced water storage in Lake Powell. The current elevation (as of July 30, 2004) of Lake Powell is 3,580 feet (120 of live capacity).
The water surface elevation at Lake Powell reached a seasonal low of 3,582.7 feet on April 2, 2004 and then increased to a seasonal high on June 14, 2004, reaching an elevation of 3,587.4 feet. The water surface has since been declining, and will likely continue to decline for the remainder of the year. Under the current inflow forecast, the water surface elevation of Lake Powell is projected to be about 3,570 feet on January 1, 2005. It should be noted that this projected elevation will likely shift, depending upon weather patterns the remainder of the year.
This Release Courtesy Tom Ryan, US Bureau of Reclamation