Releases from Glen Canyon Dam in August will average about 14,600 cubic feet per second (cfs) with a total of 900,000 acre-feet scheduled to be released. On Mondays through Fridays in August, daily fluctuations due to load following will likely vary between a low of about 10,250 cfs (during late evening and early morning off-peak hours) to a high of about 18,250 cfs (during late afternoon and early evening on-peak hours). On Saturdays, releases will likely vary between a low of about 10,250 cfs during off-peak hours to a high of about 17,750 cfs during on-peak hours. On Sundays, releases will likely be steady throughout the day at 10,250 cfs. Releases from Glen Canyon Dam in September, 2003 will be significantly lower than August. A total of 480,000 acre-feet is scheduled to be released in September, which averages out to about 8,000 cfs.
Because of the draw down condition of Lake Powell, releases from Lake Powell in water year 2003 are being scheduled to meet the minimum objective release of 8.23 million acre-feet. This is consistent with the requirements of the Criteria for Coordinated Long-Range Operation of Colorado River Reservoirs.
Daily high fluctuating releases from Glen Canyon Dam, as part of the Glen Canyon Dam experimental flows, were completed on March 31, 2003. From January through March 2003 releases ranged between a high of 20,000 cfs to a low of 5,000 cfs each day. These same high fluctuating releases are scheduled to be repeated in January through March of 2004.
The January through March high fluctuating releases were intended to benefit the endangered humpback chub. Scientists have recognized that the humpback chub population has been in general decline since highly fluctuating flows were curtailed in November of 1991. Those flows helped keep the non-native fish, especially the rainbow and brown trout, in check. The trout are thought to prey upon and compete with native fish such as the endangered humpback chub.
The experimental flows from Glen Canyon Dam received environmental clearances in December 2002. The flows were analyzed in an environmental assessment in accordance with the National Environmental Policy Act. The experimental flows are the result of ongoing studies by scientists from the United States Geological Survey and were recommended by the Glen Canyon Dam Adaptive Management Work Group, a Federal advisory committee. The experimental flows address the decline of two key resources in the Grand Canyon: sediment and population viability of endangered humpback chub. The Finding of No Significant Impact on the experimental flows can be found at http://www.uc.usbr.gov/amp/flow_fonsi.pdf.
Drought in the Colorado River basin continues. Inflow volumes have been substantially below average this year with water year 2003 being the 4th consecutive year with below average inflow to Lake Powell. April through July unregulated inflow to Lake Powell in 2003 was 3.91 million acre-feet, only 49 percent of the 30 year average. Total unregulated inflow for water year 2003 will likely be about 52 percent of average.
Snow accumulations in water year 2003 were again well below average levels. Additionally, what snowpack there was in the Upper Colorado River basin this year melted earlier than normal, with the runoff for the most part, being completed by late June. This has resulted in very low summer flows. Inflow to Lake Powell in July tallies up to only 350,000 acre-feet or 22 percent of average. Summer thunderstorms can help augment river flows in the summer, but thus far there has been only limited monsoonal precipitation in the Upper Colorado River basin. Inflow to Lake Powell as of July 31, 2003 is 5,900 cfs, 43 percent of what is usually seen in late July.
Total unregulated inflow into Lake Powell in water years 2000 and 2001 was 62 and 59 percent of average, respectively, and only 25 percent of average in 2002. Inflow in 2002 was the lowest ever observed since the completion of Glen Canyon Dam in 1963. These low inflows have reduced water storage in Lake Powell. Lake Powell reached a low water surface elevation this year of 3605 feet (95 feet from full pool) on May 1, 2003. Lake Powell reached its peak elevation on June 23, 2003 at 3616.6 feet. The current elevation of Lake Powell is 3,610.8 feet (89.2 feet from full pool). Current storage is approximately 12.8 million acre-feet (53 percent of capacity). The water surface elevation at Lake Powell will likely continue to decrease for the remainder of the year. Under expected inflows, Lake Powell will likely be near elevation 3602 feet on January 1, 2004.
This release courtesy Tom Ryan