Operations
Releases from Glen Canyon Dam will be nearly identical in October to what they were in September. In October, releases will average 8,000 cfs with a total of 492,000 acre-feet scheduled to be released. On Mondays through Saturdays in October, daily fluctuations due to load following will likely vary between a low of 5,000 cfs (during late evening and early morning off-peak hours) to a high of 10,000 cfs (during late afternoon and early evening on-peak hours). On Sundays, releases will be 5,000 cfs from 7 pm until 7 am, and 8,000 cfs from 7 am until 7 pm.
Releases from Glen Canyon Dam in November of 2003 are currently scheduled be 476,000 acre-feet (an average releases of 8,000 cfs), with the same load following pattern as October.
Because of the draw down condition of Lake Powell, releases from Lake Powell in water year 2003 were 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.
Basin Hydrology
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 be 53 percent of average.
Inflow into Lake Powell picked up somewhat in September, 2003. Significant amounts of precipitation fell in the Colorado River Basin, particularly in the Four Corners region, in the first two weeks of September. Unfortunately, a drying trend followed. There has been almost no precipitation in the Colorado River Basin in the latter part of September. Total unregulated inflow in September will end up at about 453,000 acre-feet, or 95 percent of average. Inflow on September 29, 2003 was 5,600 cfs, about 60 percent of what is usually seen in late September.
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 peak elevation in 2003 on June 23 at 3616.6 feet. The current elevation of Lake Powell is 3,603.8 feet (96.2 feet from full pool). Current storage is approximately 12.1 million acre-feet (50 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 3600 feet on January 1, 2004.
Experimental Flows
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.
This release courtesy Tom Ryan.