Glen Canyon Dam Operations
Releases from Glen Canyon Dam in May 2007 will average 10,000 cubic feet per second (cfs) with a total of 600,000 acre-feet scheduled to be released for the month. On Mondays through Fridays in May, daily release fluctuations due to load following will likely vary between a low of 6,500 cfs (during late evening and early morning off-peak hours) to a high of 12,500 cfs (during daylight and early evening on-peak hours). On Saturdays, release fluctuations will likely vary between a low of 6,500 cfs to a high of 11,750 cfs. On Sundays, release fluctuations will likely vary between a low of 6,500 cfs to a high of 11,250 cfs.
Releases from Glen Canyon Dam in June 2007 will be higher than May. A total of 800,000 acre-feet is scheduled to be released in June of 2007.
Upper Colorado River Basin Hydrology
Projections for April through July runoff to Lake Powell in 2007 remain low. The water supply picture in the Colorado River Basin neither improved nor weakened in April. April was a month with periods of above average and below average temperatures, with precipitation nearly average. The May final unregulated inflow forecast for Lake Powell is 4.0 million acre-feet. This is only 50 percent of average.
Unregulated inflow in April 2007 was 801,900 acre-feet, or 81 percent of average. Above average temperatures the final two days of April and first two days of May produced has produced a surge in streamflows. This surge in streamflows is just now reaching Lake Powell. Inflow to Lake Powell is currently 16,000 cfs (May 4, 2007) and is increasing. The peak inflow to Lake Powell for 2007 will probably occur within the next several days, with the magnitude of the peak likely near 25,000 cfs. However, Lake Powell inflow the second half of May and all of June is projected to be much below the historic average. Throughout the basin, snowpack diminished significantly as we exited April and entered May. Basinwide snowpack above Lake Powell is now only 46 percent of average (May 4, 2007).
Water year 2007 (which began on October 1, 2006) started out "wet," with October precipitation over 200 percent of average. Inflow to Lake Powell in October 2007 was 184 percent of average. Unfortunately, the pattern quickly changed. During the five-month period of November 2006 through March 2007, basinwide precipitation was below average. March 2007 was a particularly dry month, featuring above average temperatures and below average precipitation. Normally, mountain snowpack increases in March. However, in March 2007, a significant reduction in snowpack occurred, which in turn, substantially weakened the water supply picture for 2007.
The current elevation of Lake Powell (May 4, 2007) is 3,600.6 feet, 99.4 feet from full pool elevation of 3,700 feet. Reservoir storage is currently 11.80 million acre-feet, or 49 percent of capacity. The water surface elevation of Lake Powell reached a seasonal low of 3,597.4 feet on March 16, 2007. Under the current inflow forecast, Lake Powell would reach a seasonal peak elevation of about 3,606 feet in late June 2007.
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 73 percent of average.
Water year 2007 will almost certainly be a year of below average inflow. The current projection for spring runoff into Lake Powell is only 50 percent of average. Projected inflow to Lake Powell for the entire 2007 water year is 68 percent of average. With 2007 projected to be a below average inflow year, one sees that over the past 8 years (2000 through 2007, inclusive) inflow to Lake Powell will have been below average in all but one year (2005).
Reservoir storage in Lake Powell and Lake Mead has decreased over the past 8 years. Reservoir storage in Lake Powell and Lake Mead is currently 49 and 52 percent of capacity, respectively.
This release courtesy Tom Ryan, United States Bureau of Reclamation.