Glen Canyon Dam Operations
The monthly release volume in May 2008 will likely be higher than in April 2008. A total monthly volume of 790,000 acre-feet is scheduled to be released in May 2008. Weekday releases will average about 12,850 cfs with afternoon peaks to about 15,000 cfs and off peak lows to about 9,000 cfs. Saturday and Sunday releases will average about 12,300 cfs with afternoon peaks to about 14,750 cfs and off peak lows to about 9,000 cfs.
Releases from Glen Canyon Dam for the remainder of water year 2008 will be governed by the Equalization Tier of the Interim Guidelines for the Operation of Lake Powell and Lake Mead (Interim Guidelines). Under the Equalization Tier, the water year annual release volume can be above 8.23 million acre-feet (maf). For the May 2008 24-Month Study, the controlling Equalization objective for water year 2008 is an end of water year Lake Mead elevation of 1105 feet above sea level. To achieve this objective, the water year annual release from Glen Canyon Dam is projected to be 8.954 maf with an equalization volume (volume in excess of 8.23 maf) projected to be 724 kaf. These projected values, as well as the monthly release volumes, for the remaining months of water year 2008 will be adjusted as conditions change.
Upper Colorado River Basin Hydrology
Precipitation in the basin above Lake Powell was below normal in April as it was in March. The precipitation above Lake Powell in March was 60% of normal while in April the precipitation was only 65% of normal. The overall precipitation in the Upper Colorado River Basin for water year 2008 is 107% of normal. Temperature conditions in April were below normal which has preserved the snowpack conditions somewhat. As of May 6, 2008 the basin wide snowpack conditions were 102% of normal as compared to only 46% of normal on this date one year ago. Unregulated inflow to Lake Powell in April was 1,002,800 acre-feet (109% of normal) and for water year 2008 have been 3,586,200 acre-feet 95% of normal. Inflows to Lake Powell are increasing. Inflows to Lake Powell are averaging about 25,000 cfs as compared to an average of about 15,000 cfs just two weeks ago.
The April through July unregulated inflow forecast for Lake Powell was decreased from 9.7 maf (122% of normal) in April to 9.2 maf (116% of normal) for May. This reduction in the forecast has reduced the projected water surface elevations of Lake Powell for the summer months. The elevation of Lake Powell is now projected to peak in late July near 3636 feet above sea level (64 feet below the full pool elevation of 3700 feet above sea level) and is projected to end the water year near 3632.4 feet above sea level. The current (May 6, 2008) water surface elevation of Lake Powell is 3595.9 feet above sea level.
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). Drought conditions have eased again in water year 2008 with projected inflows to the main stem Colorado River reservoirs at or above normal. Reservoir storage in the Colorado River Basin, however, is still below desired levels with the overall Colorado River system storage (above Lake Mead) projected to be about 60% of capacity at the end of water year 2008.
Reservoir storage in Lake Powell and Lake Mead has decreased during the past 8 years but is projected to increase by the end of water year 2008. Current reservoir storage in Lake Powell is 46 percent of capacity. Storage in Lake Mead is 48 percent of capacity.
This release courtesy Rick Clayton, US Bureau of Reclamation