In July 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 July, daily fluctuations due to load following will likely vary between a low of about 10,500 cfs (during late evening and early morning off-peak hours) to a high of about 18,500 cfs (during late afternoon and early evening on-peak hours). On Saturdays, releases will likely vary between a low of about 10,500 cfs during off-peak hours to a high of about 17,750 cfs during on-peak hours. On Sundays, releases will likely vary between a low of about 10,500 cfs during off-peak hours to a high of about 16,500 cfs during on-peak hours. A volume of 900,000 acre-feet is scheduled to be released in August. It is expected that a load following release pattern similar to the one seen in July will be followed in August.
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 month of June was cooler than average in the Colorado River Basin. Aggregate precipitation in the basin was near average, although there was significant spatial disparity (above average precipitation in the northern areas of the basin and below average levels in the southern areas). Inflow to Lake Powell in June was 65,000 acre-feet above the June 1 projection. In the grand scheme of things, this is not a lot of water, but at least it is a move in the right direction. Inflow projections remain low, however. The National Weather Service's July preliminary forecast is calling for 3.475 million acre-feet of unregulated inflow to Lake Powell during the April through July runoff period, only 44 percent of average.
The month of March pretty much 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 now in 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 50 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 June 30, 2004 observed inflow to Lake Powell was 10,000 cfs about 32 percent of what is normally seen as June comes to a close. Total unregulated inflow to Lake Powell in March, April, and May of this year was 81, 83, and 51 percent of average, respectively. Inflow in June was 1,095,000 acre-feet, or 36 percent of average. Unless there is a summer monsoon in the Colorado River Basin, inflow in July could be less than 30 percent of average. There are only limited amounts of mountain snowpack remaining in the basin.
Low inflows the past 5 years have reduced water storage in Lake Powell. The current elevation (as of July 1, 2004) of Lake Powell is 3,586.1 feet (113.9 feet from full pool). Current storage is 10.5 million acre-feet (43 percent 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 begun to decline, 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