Releases from Glen Canyon Dam in May will average about 10,600 cubic feet per second (cfs) with a total of 650,000 acre-feet scheduled to be released. On Mondays through Fridays in May, daily fluctuations due to load following will likely vary between a low of about 7,250 cfs (during late evening and early morning off-peak hours) to a high of about 13,250 cfs (during late afternoon and early evening on-peak hours). On Saturdays, releases will likely vary between a low of about 7,250 cfs during off-peak hours to a high of about 11,750 cfs during on-peak hours. On Sundays, releases will likely vary between a low of about 7,250 cfs during off-peak hours to a high of about 8,000 cfs during on-peak hours.
Over Memorial Day weekend, there will be three-and-a-half days where releases are held at 8,000 cfs. Releases will be ramped down the afternoon of May 23 so that the 8,000 cfs release is achieved by 6 p.m. mountain standard time. This 8,000 cfs flow will then be maintained through the holiday weekend until Tuesday morning (May 27), when a normal load-following pattern is reestablished. This 8,000 cfs release is being made as part of the Grand Canyon Monitoring and Research Center's annual over flight for data collection essential for research and long-term monitoring of the Grand Canyon.
June releases will be moderately higher than May. A total of 840,000 acre-feet is scheduled to be released in June 2003, which averages out to 14,100 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 1970 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 20,000 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.
Basin Hydrology
Upper Colorado River Basin snowpack is currently 71 percent of average (as of May 2, 2003). The May preliminary inflow forecast issued by the National Weather Service is calling for 4.4 million acre-feet of unregulated runoff into Lake Powell during the 2003 April through July time period. This equates to 55 percent of average. The inflow forecast has been reduced from that forecasted in April. The April final forecast was calling for inflow of 66 percent of average. Periods of warm windy weather took a toll on the mountain snowpack in April. Such warm windy conditions increase sublimation losses from the snowpack, and also increase evaporation losses from the soil.
Unregulated inflow in April 2003 was disappointing with the total being only 409,000 acre-feet (42 percent of average). Inflow to Lake Powell has been significantly below average throughout water year 2003. Unregulated inflow into Lake Powell in January, February, and March was only 58, 62, and 62 percent of average, respectively.
Drought conditions persist in the Colorado River Basin with 2003 being the 4th consecutive year with below average inflow. 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. The current elevation of Lake Powell is 3,605.0 feet (95.0 feet from full pool). Current storage is approximately 12.2 million acre-feet (50 percent of capacity). The water surface elevation of Lake Powell is now at the low for the year, and will be increasing throughout the month of May. Under the current inflow forecast, Lake Powell will only reach a peak water surface elevation of about 3,615 feet this year in late June or early July. However, this projected elevation will likely shift somewhat depending on weather patterns for the remainder of the spring and summer.
This release courtesy Tom Ryan