Upper Colorado River Basin Hydrology
The Colorado River Basin has now completed 5 consecutive years of severe drought. In the summer of 1999 Lake Powell was essentially full, with reservoir storage at 97 percent of capacity. Since that time, inflow volumes have been below average for 5 consecutive water years. Total unregulated inflow to Lake Powell in water year 2004 was only 51 percent of average. Unregulated inflow in water years 2000, 2001, 2002, and 2003 was 62, 59, 25, and 51 percent of average, respectively. Inflow in water year 2002 was the lowest ever observed since the completion of Glen Canyon Dam in 1963.
Hydrologic conditions have improved over the past 6 months in the Colorado River Basin. Since September 2004, precipitation in the basin has been above average. Snowpack in the basin above Lake Powell is currently 116 percent of average (as of March 8, 2005).
Inflow to Lake Powell, as a percentage of average, has increased since last summer in response to the precipitation events last fall and winter. November 2004 was the first month with above average inflow to Lake Powell since September 1999. Unregulated inflow in January and February was 128 and 118 percent of average, respectively.
As of March 8, 2005, the elevation of Lake Powell is 3,558.4 feet (141.6 feet from full pool). Current storage is 8.21 million acre-feet (34 percent of live capacity).
The National Weather Service (in their March final inflow forecast) is forecasting 8.6 million acre-feet of unregulated inflow to Lake Powell this April through July. This is 108 percent of average.
The water surface elevation of Lake Powell is projected to gradually decline until early-April 2005. Current projections show the lake decreasing to an elevation of about 3,556 feet by early-April. The elevation of Lake Powell is projected to increase from April through mid-July of 2005. Current projections (using the March final inflow forecast) show Lake Powell reaching a peak water surface elevation in July 2005 of about 3,603 feet.
It should be noted, however, there is uncertainty with these projections. Weather conditions this spring will likely result in shifts to inflow projections in 2005.
Operations * Experimental Releases
Daily high fluctuating releases from Glen Canyon Dam, as part of the Glen Canyon Dam experimental flows, are being implemented from January 2, 2005 through the first week of April 2005. On Mondays through Saturdays, releases will range between 5,000 cubic feet per second (cfs) and 20,000 cfs. The 20,000 cfs release will be maintained for about 11 hours (from 9:00 am until about 8:00 pm) and the 5,000 cfs release will be maintained for about 6 hours (from 1:00 am until about 7:00 am). The other hours are transitional, where releases will be between the daily high and the daily low. Releases on Sundays will range 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. These 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 third consecutive year of high fluctuating winter releases.
The monthly release volume in March 2005 is scheduled to be 807,000 acre-feet, which averages out to about 14,000 cfs per day on Mondays through Saturdays and 6,700 cfs per day on Sundays. On April 8, 2005 high fluctuating releases are scheduled to end. Releases will be lower in April. A volume of 505,000 acre-feet is scheduled to be released in April.
On November 21, 2004, releases from Glen Canyon Dam were increased for a high-flow experiment. Releases were increased to 41,000 cfs, with this release level maintained for 60 hours. For additional information on the high-flow experiment go to: http://184.108.40.206/uc/feature/GCtestflow/index.html
Because of the draw down condition of Lake Powell, releases from Lake Powell in water year 2005 are being scheduled to meet the minimum release objective of 8.23 million acre-feet. Experimental releases will not change the total volume of water to be released from Lake Powell in water year 2005.
This release courtesy Tom Ryan, USBOR