May 2004. Upper Colorado River Basin Hydrology
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. Basinwide snowpack dropped over 30 percentage points in March.
As we move through the spring, inflow projections continue to be lowered. The National Weather Service May mid-month forecast is calling for 3.4 million acre-feet of unregulated inflow to Lake Powell during the April through July runoff period, only 43 percent of average. This is a sizable reduction from the volume forecasted in March.
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 now 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 and April approached average levels as abnormally warm temperatures melted out significant amounts of snow in the basin. Unregulated inflow in March was 538,000 acre-feet, 81 percent of average. April unregulated inflow was 816,000 acre-feet, 83 percent of average. Unfortunately the inflows seen in March an April are at the expense of May and June inflows (when the largest inflow volumes are normally observed). Inflow in May will likely be less than 50 percent of average. Peak inflow to Lake Powell the year likely occurred on May 14 when inflow was 21,400 cfs. As of May 24, 2004 inflow to Lake Powell is 18,700 cfs about 49 percent of what is normally seen in late May.
Low inflows the past 5 years have reduced water storage in Lake Powell. The current elevation (as of May 24, 2004) of Lake Powell is 3,586 feet (114 feet from full pool). Current storage is 10.5 million acre-feet (43 percent of live capacity).
The water surface elevation at Lake Powell reached a seasonal low of 3,682.7 feet on April 2, 2004. The water surface elevation of Lake Powell is currently slowly rising, but will likely not exceed elevation 3,590 feet. By mid-June the water surface elevation will likely begin to decrease. Under the current inflow forecast, the water surface elevation of Lake Powell is projected to be about 3,570 feet on January 1, 2005. It should be noted that this projected elevation will likely shift, depending upon weather patterns the remainder of the year.
Operations * Steady Releases Memorial Weekend
Over the Memorial Day weekend, releases from Glen Canyon Dam will be steady at 8,000 cfs. Contractors working for the Grand Canyon Monitoring and Research Center will be collecting airborne images to support the long-term monitoring of the Grand Canyon. Planes collecting the data will be flying at an altitude of 4,500 feet above the river corridor. The steady 8,000 cfs release will begin at 1800 hours on Friday May 28, 2004. Releases will be held at 8,000 cfs until the data collection is complete, at which time a normal load-following pattern will be reestablished. The 8,000 cfs steady release could end as early as Monday May 31, or possibly extend to Wednesday, June 2 (no later than 1600 hours), depending upon weather conditions.
Releases from Glen Canyon Dam from May 25 through the afternoon of May 28 (when the steady 8,000 cfs release begins) will likely vary between a low of about 6,600 cfs (during late evening and early morning off-peak hours) to a high of about 12,600 cfs (during late afternoon and early evening on-peak hours).
In June 2004, a volume of 800,000 acre-feet is scheduled to be released from Lake Powell, which is an average of 13,400 cfs. On Mondays through Fridays in June, daily fluctuations due to load following will likely vary between a low of about 9,000 cfs (during late evening and early morning off-peak hours) to a high of about 17,000 cfs (during late afternoon and early evening on-peak hours). On Saturdays, releases will likely vary between a low of about 9,000 cfs during off-peak hours to a high of about 16,000 cfs during on-peak hours. On Sundays, releases will likely vary between a low of about 9,000 cfs during off-peak hours to a high of about 15,000 cfs during on-peak hours. A volume of 898,000 acre-feet is scheduled to be released in July which is an average release of 14,600 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.
This Release Courtesy Tom Ryan, US Bureau of Reclamation