Lake Powell - Glen Canyon Dam - Current Status
Glen Canyon Dam Operations
In March 2008, a high flow test will be implemented. Based on information from scientific monitoring and research activities and stakeholder discussions in the Glen Canyon Dam Adaptive Management Program, Reclamation has proposed and will conduct a high flow experiment beginning on March 4, 2008 at 22:00 MST. The release characteristics of this experiment will be identical to the test conducted in November2004 with a peak release magnitude of 41,500 cfs and a duration of 60 hours. A gradual ramp up to this peak will begin on March 4, 2008 at 22:00 MST. On March 5, 2008 at approximately 10:00 MST, Glen Canyon Powerplant will be releasing approximately26,500 cfs and bypass releases will begin to ramp up. The peak release of 41,500 cfs is scheduled to begin on March 6, 2008 at approximately 4:00 MST and will be maintained for 60 hours to be followed with a gradual ramp down to normal operations by March 10,2008.
The purpose of this test will be to determine the effectiveness of rebuilding and reworking sandbar deposits and backwaters in Marble and Grand Canyons. An Environmental Assessment has been completed by Reclamation and a Finding of No Significant Impact was signed on February 29, 2008 clearing Reclamation to conduct this experiment. More information is available at the following URL:
http://www.usbr.gov/uc/envdocs/ea/gc/2008hfe/index.html
The scheduled release volume for March 2008 will be increased to 830,000 acre-feet to accommodate this experiment. The elevation of Lake Powell is anticipated to decrease by about 2.3 feet during the high flow experiment. However, the annual release volume from Glen Canyon Dam during water year 2008 will be unaltered by the experiment. Monthly release volumes later this year will be adjusted downward to account for the additional water released in March. The Lake Powell water surface elevation at the end of water year 2008 will not be affected by the high flow experiment.
The high flow experiment is scheduled to be completed by March 10, 2008. Releases from Glen Canyon Dam, after the experiment is completed, for the remaining days of March, will average about 10000 cfs on weekdays with daily fluctuations between 7000 cfs to 13000 cfs. On weekends, releases will average about 9000 cfs with fluctuations between 7000 cfs and 13,000.
Upper Colorado River Basin Hydrology
Precipitation in the Upper Colorado River Basin was 124 % of average in February 2008. After a very poor beginning to water year 2008, precipitation for the water year has made a remarkable comeback and is now 121% of average as of March 2, 2008. Basin-wide snowpack was only 35 % of average on November 29, 2007, but has increased steadily since the first week of December 2007. As of March 2, 2008 the snowpack conditions above Lake Powell are 124% of average. The climate outlook for the Upper Colorado River Basin indicates that the next 3 months will likely have below normal precipitation and above normal temperatures.
Inflow to Lake Powell is currently 11,100 cfs (March 2, 2008). Total unregulated inflow to Lake Powell so far in water year 2008 (October through February) is 84 percent of average with February measured at 102 % of average.
Forecasted April through July unregulated inflow to Lake Powell in 2008 is 9.5 million acre-feet, 120 % of average (February mid-month forecast). This forecast will be updated later this week. Typically by March 1st, the snow accumulation season is about 80% complete in the Upper Colorado River Basin.
The current elevation of Lake Powell (March 2, 2008) is 3,590.7 feet, 109.3 feet from full pool elevation of 3,700 feet. Reservoir storage is currently 10.88 million acre-feet, or 45 percent of capacity. The water surface elevation of Lake Powell is now near its seasonal low. In April, anticipated snowmelt runoff will cause the water surface elevation to begin to increase. Under the current inflow forecast, Lake Powell would reach a peak elevation of about 3639 feet in July 2008. The peak elevation for Lake Powell in 2007 was 3,611.7 feet.
Upper Colorado River Basin Drought
The Upper Colorado River Basin is experiencing a protracted multi-year drought. Since 1999, inflow to Lake Powell has been below average in every year except one. In the summer of 1999, Lake Powell was essentially full with reservoir storage at 23.5 million acre-feet, or 97 percent of capacity. Inflow to Lake Powell in 1999 was 109 percent of average. The manifestation of drought conditions in the Upper Colorado River Basin began in the fall months of 1999. A five year period of extreme drought occurred in water years 2000, 2001, 2002, 2003, and 2004 with unregulated inflow to Lake Powell only 62, 59, 25, 51, and 49 percent of average, respectively. Lake Powell storage decreased through this five-year period, with reservoir storage reaching a low of 8.0 million acre-feet (33 percent of capacity) on April 8, 2005.
Drought conditions eased in water year 2005 in the Upper Colorado River Basin. Precipitation was above average in 2005 and unregulated inflow to Lake Powell was 105 percent of average. Lake Powell increased by 2.77 million acre-feet (31 feet in elevation) during water year 2005. But as is often the case, one favorable year does not necessarily end a protracted drought. In 2006, there was a return to drier conditions in the Colorado River Basin. Unregulated inflow to Lake Powell in water year 2006 was only 71 percent of average.
Water year 2007 was another year of below average inflow with unregulated inflow into Lake Powell at 68 percent of average. Over the past 8 years (2000 through 2007, inclusive), inflow to Lake Powell has been below average in all but one year (2005). Reservoir storage in Lake Powell and Lake Mead has decreased during the past 8 years. Reservoir storage in Lake Powell is 45 percent of capacity. Storage in Lake Mead is 50 percent of capacity.
This release courtesy Rick Clayton, US Bureau of Reclamation