Glen Canyon Dam Update August 2010

Glen Canyon Dam / Lake Powell

The unregulated inflow volume into Lake Powell for July 2010 through July 21st is 550 thousand acre feet (kaf) and at the current inflow rate, the inflow volume for July 2010 will likely be approximately 674 kaf (43% of average). Observed inflows peaked for water year 2010 on June 12, 2010 at 57,600 cubic feet per second (cfs). Since that time inflows have steadily declined and as of July 21, 2010 inflows had decreased to 6,250 cfs. The low water surface elevation for water year 2010 occurred on April 15, 2010 when the elevation dipped to 3618.64 feet above sea level. Since that date the elevation has been on the rise and reached a peak of 3638.82 on June 30, 2010. This will likely be the peak elevation for water year 2010 as inflows are projected to fall below release rates during the next week. The overall elevation increase for water year 2010 was just over 20 feet. By the end of water year 2010 the elevation is projected to be roughly 3634.7 feet above sea level. The April through July forecasted unregulated inflow to Lake Powell is currently 5.77 maf (73% of average) based on the July midmonth forecast. 

Releases from Glen Canyon Dam during the month of July will fluctuate each day for power generation between a peak hourly average release of about 16,500 cfs, during the morning and afternoon and a daily low hourly average release of 8,500 cfs during the late evening and early morning hours. The release volume scheduled for July is 800,000 acre-feet. The release volume for August will be approximately 800,000 acre-feet. 

Bureau of Reclamation officials are projecting August flows to be the same as July flows at this time, between a peak hourly average release of about 16,500 cfs, during the morning and afternoon and a daily low hourly average release of 8,500 cfs during the late evening and early morning hours.

In addition to the daily fluctuation pattern, instantaneous releases from Glen Canyon Dam also fluctuate to provide approximately 40 megawatts (approximately 1,100 cfs) of system regulation to maintain stable conditions within the electrical generation and transmission system. This translates into momentary release fluctuations of about +/- 1100 cfs above or below the hourly average release rate. These momentary fluctuations for regulation are very short lived and typically balance out over the hour. When an unanticipated outage event occurs in the generation system, reserve generation at Glen Canyon Dam can also be called upon up to a limit of 83 megawatts (approximately 2,250 cfs of release) for a duration of 2 hours or less. Under normal circumstances, calls for reserve generation occur fairly infrequently and are for much less than the limit of 83 megawatts. 

On September 1, 2010 and continuing through October 31, 2010, the releases from Glen Canyon Dam will be steady with no fluctuations for power production (excluding system regulation and spinning reserves) for a steady flow experiment pursuant to the February 2008 Finding of No Significant Impact 'Experimental Releases from Glen Canyon Dam, Arizona 2008 through 2012'. This year will be the third year of steady flows of the 5 year experiment. The projected release rate being targeted is 8,000 cfs which is equivalent to a monthly release volume of approximately 476,000 acre-feet in September 2010 and 492,000 acre-feet in October 2010. At the end of August, for a period of approximately 3 days, the daily fluctuation schedule will change each day in order to gradually transition to the steady release rate of 8,000 cfs to begin on September 1, 2010. 

Pursuant to the Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lakes Powell and Mead (Interim Guidelines) the operational tier for water year 2010 is Upper Elevation Balancing and the projected water year release volume is 8.23 million acre feet (maf). Under this operational tier there was a possibility that Equalization could occur in 2010 if the April 2010 24-Month Study,with 8.23 maf projected for release during water year 2010, indicated a Lake Powell projected elevation on September 30 , 2010 greater than 3642 feet above sea level (the Equalization level for water year 2010). This condition was not projected in the April 24-Month Study and for this reason, the release volume for water year 2010 will be 8.23 maf. Monthly release volumes for the remainder of the water year will be scheduled to achieve this water year release volume. 

The July 2010 24-Month Study projects that operation tier for Glen Canyon Dam in water year 2011 will be Upper Elevation Balancing but also projects a shift to Equalization in April 2011. The projected water year 2011 release volume is 11.5 maf. It should be cautioned however that at this time of year, the inflow assumptions used in the 24-Month Study for the following water year are based on statistical averages and do not reflect current hydrologic conditions. There is a high level of uncertainty about what the inflow conditions will be in water year 2011. In August 2010 the Colorado Basin River Forecast Center will issue an inflow projection for water year 2011 and this will be the basis of the inflow assumptions used in the August 2010 24-Month Study. It is currently forecasted that there is approximately a 59% probability that Equalization will occur in water year 2011. This forecast will be updated each month as conditions change. 

The July 2010 24-Month Study has been published and will be available here:

Updated elevation projections for Lake Powell through water year 2010 based on the most recently published 24-Month Study are maintained at:

Upper Colorado River Basin Hydrology

In the Upper Colorado River Basin during water year 2009, the overall precipitation accumulated through September 30, 2009 was approximately 95% of average based on the 30 year average for the period from 1971 through 2000. For water year 2010 dry conditions have persisted. Estimated percentages of average precipitation for the months thus far in water year 2010 are as follows: October 85%, November 40%, December 130%, January 100% and February 100%, March 90%, April 120%, May 75%, June 100%, . The overall estimated precipitation percentage of average thus far in water year 2010 for the Upper Colorado River Basin is 87% of average. 

The Climate Prediction Center outlook (dated July 15, 2010) for temperature over the next 3 months indicates that temperatures in the Upper Colorado River Basin are expected to be above average while precipitation over the next 3 months is projected to be below average.

Upper Colorado River Basin Drought

The Upper Colorado River Basin continues to experience a protracted multi-year drought. Since 1999, inflow to Lake Powell has been below average in every year except water years 2005 and 2008. In the summer of 1999, Lake Powell was close to full with reservoir storage at 23.5 million acre-feet, or 97 percent of capacity. During the next 5 years (2000 through 2004) unregulated inflow to Lake Powell was well below average. This resulted in Lake Powell storage decreasing during this period to 8.0 million acre-feet (33 percent of capacity) which occurred on April 8, 2005. During 2005, 2008 and 2009, drought conditions eased somewhat with net gains in storage to Lake Powell. As of July 21, 2010 the storage in Lake Powell was 15.73 million acre-feet (64.7 % of capacity) which is still below desired levels while the overall reservoir storage in the Colorado River Basin as of June 30, 2010 is 34.37 million acre-feet (57.8 % of capacity).