Glen Canyon Dam - Lake Powell
The month of March pretty much dashed hopes that 2004 would bring relief to the ongoing drought in the Colorado River Basin. Basin snowpack on March 1, 2004 was 96 percent of average. At that time the April through July inflow was forecasted to be 82 percent of average. The weather pattern in March, 2004 was very dry and extremely warm for early spring. Temperatures around the basin for much of the month were 20 degrees above average. As of April 2, 2004 snowpack in the basin has fallen to 67 percent of average, a drop of almost 30 percentage points in just one month. The low elevation snow (below 6,000 feet) in the basin is now gone and much of the mid-elevation snow (6,000 to 9,000 feet) has melted out as well. While river flows increased in late March, these increases were not nearly enough to offset this early season loss of snow and the possibility of better runoff conditions in May and June. The National Weather Service April preliminary forecast is calling for 4.4 million acre-feet of unregulated inflow to Lake Powell during the April through July runoff period, only 55 percent of average. This is a sizable reduction from the volume forecasted only a month ago. The final forecast will be issued on April 5.
So, the drought continues. The Colorado River Basin is now in its 5th year of drought. Inflow volumes have been below average for 4 consecutive years, with 2004 almost certain to follow suit. 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.
Inflow to Lake Powell in March 2004 picked up as the abnormally warm and dry weather pattern melted out significant amounts of snow in the basin. Even so, March inflow ended up below normal. Unregulated inflow in March was 538,000 acre-feet, 81 percent of average. A large portion of the melting snow last month was absorbed by the dry soils in the basin. As of April 2, 2004 inflow to Lake Powell is 8,700 cfs about 75 percent of what is normally seen in early April.
Low inflows the past 5 years have reduced water storage in Lake Powell. The current elevation (as of April 2, 2004) of Lake Powell is 3,587 feet (113 feet from full pool). Current storage is 10.2 million acre-feet (42 percent of live capacity).
The water surface elevation of Lake Powell is nearing its seasonal low. The water surface elevation will likely remain near elevation 3,587 in April and then increase some in May and June. Under the current inflow forecast, however, it's almost certain that Lake Powell will remain below elevation 3,600 feet in 2004.
Operations * Experimental Flows
In April 2004, a volume of 650,000 acre-feet is scheduled to be released from Lake Powell, which is an average of 10,900 cubic feet per second (cfs). On Mondays through Fridays in April, daily fluctuations due to load following will likely vary between a low of about 7,800 cfs (during late evening and early morning off-peak hours) to a high of about 13,800 cfs (during late afternoon and early evening on-peak hours). On Saturdays, releases will likely vary between a low of about 7,800 cfs during off-peak hours to a high of about 12,500 cfs during on-peak hours. On Sundays, releases will likely vary between a low of about 7,800 cfs during off-peak hours to a high of about 12,000 cfs during on-peak hours. A volume of 600,000 acre-feet is scheduled to be released in May which is an average release of 9,760 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.
Daily high fluctuating releases from Glen Canyon Dam, as part of the Glen Canyon Dam experimental flows, were implemented from January through March 2004. Releases, each day, varied between a low of 5,000 cfs to a high of 20,000 cfs (except for Sundays in February and March) throughout this period. The experimental flows will not change the total volume of water to be released from Lake Powell in water year 2004.
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.
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