Glen Canyon Dam - Lake Powell
Drought conditions in the Colorado River Basin continue. While snowpack conditions this year are better than they have been in the past 4 years, there are no strong signals that there has been significant amelioration of the drought. In late December and early January there were a number of storms in the Colorado River Basin. Early January snowpack showed some promise with the basinwide 'pack' getting as high as 115 percent of average by January 8. The pattern since that time has been drier than average, however. As of February 27, 2004, snowpack in the Colorado River Basin is 92 percent of average. Because of the extended drought, the snowpack lies atop a mantle of very dry soil. This scenario is not favorable for this spring's runoff, as much of the melting snow will be absorbed by the soil. The National Weather Service's February mid-month inflow forecast is calling for 6.0 million acre-feet of unregulated inflow to Lake Powell in April through July. This is only 76 percent of average.
The Colorado River Basin is now in its 5th year of drought. Inflow volumes have been below average for 4 consecutive years. Unregulated inflow in water year 2003 was only 53 percent of average. Unregulated inflow in 2000, 2001 and 2002 was 62, 59, and 25 percent of average, respectively. Inflow in 2002 was the lowest ever observed since the completion of Glen Canyon Dam in 1963. While snowpack and runoff projections this year are better than they have been the past 4 years, it's looking like 2004 will be another year with below average inflow. Only a 'wetter' than average spring in the Colorado River Basin could result in this year's runoff being above average.
The trend of low inflow continues. Unregulated inflow November, December, and January was only 64, 67 and 74 percent of average, respectively. On February 26, 2004 observed inflow to Lake Powell was 5,000 cfs, about 50 percent of what is usually seen in late February.
Low inflows have reduced water storage in Lake Powell. The current elevation (as of February 27, 2004) of Lake Powell is 3,587 feet (113 feet from full pool). Current storage is 10.5 million acre-feet (43 percent of capacity). The good news is that even after 4 years of extreme drought, Lake Powell is still storing a large volume of water.
The water surface elevation of Lake Powell is nearing its seasonal low. The water surface elevation will likely decrease for another 6 weeks at which time inflow will surpass releases and the lake will begin to rise. Under the current inflow forecast, Lake Powell will likely reach a peak elevation this year of about 3,602 feet in early July. It should be noted, however, there is considerable uncertainty with this projection. Weather conditions this spring will ultimately determine exactly much runoff there will be into Lake Powell during this year's April through July runoff.
Operations * Experimental Flows
Daily high fluctuating releases from Glen Canyon Dam, as part of the Glen Canyon Dam experimental flows, are being implemented from January through March 2004. On Mondays through Saturdays, releases are ranging between 5,000 cubic feet per second (cfs) and 20,000 cfs. The 20,000 cfs release is being maintained for about 11 hours (from 9:00 am until about 8:00 pm) and the 5,000 cfs release is being maintained for about 6 hours (from 1:00 am until about 7:00 am). The remainder of the hours are transitional, where releases were between the daily high and the daily low. Releases on Sundays are ranging between a low of about 5,000 cfs to a high of about 8,000 cfs.
The January through March high fluctuating releases are 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. This is the second year of high fluctuating releases as part of the experimental flows. High fluctuating releases were first implemented in January through March of 2003.
Monthly release volumes in February, and March 2004 are scheduled to be 744,000 and 807,000 acre-feet, respectively, which averages out to about 13,000 cfs per day. In April, high fluctuating releases will end. Releases in April, 2004 will likely be 650,000 acre-feet which averages out to about 10,900 cfs. Because of the draw down condition of Lake Powell, releases from Lake Powell in water year 2004 are being scheduled to meet the minimum release objective of 8.23 million acre-feet. This is consistent with the requirements of the Criteria for Coordinated Long-Range Operation of Colorado River Reservoirs. The experimental flows will not change the total volume of water to be released from Lake Powell in water year 2004.
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, US Bureau of Reclamation