Releases from Glen Canyon Dam in April will average about 10,100 cfs with the total of 600,000 acre-feet scheduled to be released. On Mondays through Saturdays in April, daily fluctuations due to load following will likely vary between a low of about 6,600 cfs (during late evening and early morning off-peak hours) to a high of about 12,600 cfs (during late afternoon and early evening on-peak hours). On Sundays, releases will likely vary between a low of about 6,600 cfs during off-peak hours to a high of about 8,000 cfs during on-peak hours.
May releases will likely be similar to April, but slightly higher. A total of 650,000 acre-feet is scheduled to be released in May, 2003 which averages out to 10,600 cfs.
Basin Hydrology
Upper Colorado River basin snowpack is currently 84 percent of average (as of April 2, 2003) The April preliminary inflow forecast issued by the National Weather Service is calling for 5.2 million acre-feet of unregulated runoff into Lake Powell during the 2003 April through July time period. This is 66 percent of average.
Drought conditions persist in the Colorado River Basin. Conditions improved somewhat in February and March with basinwide precipitation above average in both months. Precipitation in February was 150 percent of average. Final numbers for March precipitation are not yet available but will likely show precipitation that was moderately above average. December, 2002 and January, 2003 were very dry months, however. Basinwide precipitation in December and January was only 60 and 35 percent of average, respectively. It should be noted that the major snowstorm that hit Denver and the Front Range in mid-March was east of continental divide and did not contribute significant moisture to the Colorado River basin.
Inflow to Lake Powell continues to be below average. Unregulated inflow into Lake Powell in October, November, December, January, and February was 56, 69, 57, 58 and 62 percent of average, respectively. Unregulated inflow in March, 2003 was 413,000 acre-feet. Like February, this was only 62 percent of average.
Drier than average conditions have now prevailed for the past four years in the Colorado River Basin. Total unregulated inflow into Lake Powell in water year 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 3,607.0 feet (93.0 feet from full pool). Current storage is approximately 12.4 million acre-feet (51 percent of capacity). The water surface elevation of Lake Powell is now just about at the low for the year. The water surface elevation may drop another one to two feet before inflow picks up later this month. Under the current inflow forecast Lake Powell will reach a peak water surface elevation between 3,615 and 3,620 feet this year in late June or early July.
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 Releases, were completed on March 31, 2003. From January through March, 2003 releases ranged between a high of 20,000 cubic feet per second (cfs) to a low of 5,000 cfs each day.
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. These same high fluctuating releases are scheduled to be repeated in January through March of 2004.
The experimental releases 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 releases 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 releases can be found at http://www.uc.usbr.gov/amp/flow_fonsi.pdf
This release courtesy Tom Ryan