Operations
Releases from Glen Canyon Dam in July 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 July, 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 17,250 cfs during on-peak hours. On Sundays, releases will likely be steady throughout the day at 10,250 cfs.
August releases will likely be very similar to July releases. A total of 900,000 acre-feet, the same volume as July, is scheduled to be released in August, 2003. Releases in September, 2003, however, will be significantly lower. 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.
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 20,000cfs 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.
Basin Hydrology
Unseasonably warm weather was manifest in the Colorado River basin in the latter part of May and early June. This warm weather resulted in substantial late May and early June snowmelt and runoff, especially in the Yampa River basin and the headwaters drainages of the Colorado River. Some streamflow gages even recorded record high daily flows (the Eagle River in Colorado for example). Unfortunately, snow in the basin was about gone by mid-June, and river flows (which in normal years often sustain good flows throughout June) dropped off rapidly. Unless there is significant monsoonal activity this summer, river flows in the basin in July, August and September will be quite low.
Inflow to Lake Powell peaked at 53,000 cfs on June 5, 2003. The last time inflow to Lake Powell was this high was in June of 1999. As of June 30, 2003, however, inflow to Lake Powell had dropped to 12,500 cfs, only 32 percent of what would normally be seen on this date.
Inflow volumes are expected to be substantially below average this year with water year 2003 being the 4th consecutive year with below average inflow to Lake Powell. The June mid-month inflow forecast issued by the National Weather Service is calling for 4.25 million acre-feet of unregulated runoff into Lake Powell during the 2003 April through July runoff period. This equates to 54 percent of average. Total unregulated inflow for water year 2003 will likely be about 56 percent of average.
While inflow to Lake Powell was relatively healthy the a couple of weeks in late May and early June, monthly inflow volumes continue to be significantly below long term averages. Total unregulated inflow in June, 2003 will be about 2,000,000 acre-feet (65 percent of average). Unregulated inflow in January, February, March, April, and May was 58, 62, 62, 42, and 50 percent of average, respectively. 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 3,616.3 feet (83.7 feet from full pool). Current storage is approximately 13.4 million acre-feet (55 percent of capacity). The water surface elevation at Lake Powell will likely continue to decrease for the remainder of the year. Under the current inflow forecast, Lake Powell will likely be near elevation 3606 feet on January 1, 2004.
This release courtesy Tom Ryan