Glen Canyon Dam Operations
The monthly release volume for September 2008 is scheduled to be 719,000 acre-feet. During the months of September and October, releases from Glen Canyon Dam will be steady as described in the Final Environmental Assessment for Experimental Releases from Glen Canyon Dam, Arizona, 2008 through 2012 (EA). Beginning on September 1, 2008, releases from Glen Canyon Dam will be steady at 12,083 cfs and will remain at this level through the end of the day on October 31, 2008. The monthly volume for October 2008 that corresponds to this steady release rate is 743,000 acre-feet.
The water year release volume from Glen Canyon Dam in water year 2008 is being determined under the Equalization Tier of the Interim Guidelines. Under the Equalization Tier, the water year release volume in 2008 is being adjusted each month in order to target an end of water year elevation at Lake Mead of 1105 feet above sea level. Based on system conditions as of August 26, 2008 and projected operations at Lake Mead for the remainder of water year 2008, the release volume from Glen Canyon Dam for September 2008 will be set to 719 kaf which corresponds to the steady release rate of 12,083 cfs. This adjustment is being made now in order to implement the steady flows which are to begin on September 1, 2008.
Upper Colorado River Basin Hydrology
Precipitation in the basin above Lake Powell was above average in July (150% of average). The overall precipitation in the Upper Colorado River Basin for water year 2008 so far has been 105% of average.
The unregulated inflow to Lake Powell during the April through July period was 8.84 maf (111% of average). Unregulated inflow to Lake Powell from now to the end of October is projected to be above average (106%). The long range outlook for water year 2009 projects that the most probable unregulated inflow to Lake Powell will be 91% of the 30-year average (1971-2000) however there is a wide range of uncertainty associated with these long range outlooks.
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 water year 2005 and 2008.
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 9 years (2000 through 2008, inclusive), inflow to Lake Powell has been below average in all but two years (2005 and 2008). Drought conditions have eased in water year 2008 with above average inflows to the main stem Colorado River reservoirs with the exception of Flaming Gorge and Fontenelle Reservoirs. 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 58% 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 61 percent of capacity. Storage in Lake Mead is 46 percent of capacity.
This release courtesy Rick Clayton, Hydraulic Engineer, Upper Colorado Region US Bureau of Reclamation.