Glen Canyon Dam Lake Powell
The unregulated inflow volume into Lake Powell for August 2010 was 504 thousand acre feet (kaf) or 82% of average. The elevation of Lake Powell decreased during the month of August by approximately 2 feet from 3636.5 feet at the beginning of August to 3634.5 feet at the end of August. This ending elevation corresponds to a live storage of 15.37 million acre feet (maf) which is 63.2% of the full capacity. During the month of August the release volume from Glen Canyon Dam was 801.7 kaf and the hourly releases during most days fluctuated for power generation between a peak of 16,500 cubic feet per second (cfs) during the day and a low of 8,500 cfs during the evening and early morning.
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 the 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 steady release rate 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.
During the steady flow experiment the instantaneous releases from Glen Canyon Dam may fluctuate somewhat 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 targeted steady release target (8000 cfs). These momentary fluctuations for regulation are very short lived and will typically balance out over the hour. Spinning and non-spinning reserve generation will also be carried at Glen Canyon Dam during the steady flow experiment. 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.
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 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 August 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 in operations where Equalization will govern the operation beginning in April 2011. The most probable run of the August 24-Month Study projects the water year 2011 release volume to be 11.58 maf. At this point in time, there is a high level of uncertainty regarding the hydrologic conditions that will be experience in 2011. The August 24-Month Study, which includes analysis of a range of possible inflow scenarios in water year 2011, projects that the most probable range of annual releases from Lake Powell will be from 9.0 maf to 14.1 maf. It is currently forecasted that there is approximately a 62% probability that Equalization will occur in water year 2011. This forecast will be updated each month as conditions change.
The unregulated inflow forecast (dated September 1, 2010) for Lake Powell projects the most probable unregulated inflow volumes for the next 3 months as follows: (Sepember-400 kaf [84% of average], October-475 kaf [87% of average], November-460 kaf [84% of average]). The water year outlook for water year 2011 (dated August 3, 2010) projects that the most probable unregulated inflow to Lake Powell during water year 2011 will be 10.75 maf [89% of average]. The probable range [80% probability of occurrence] for the unregulated inflow during water year 2011 is projected to be from 5.0 maf (dry) to 17.1 maf (wet). The water year outlook for 2011 will be updated during the first week of October, 2010.
The September 2010 24-Month Study will be published by September 8th, 2010 and will made available here:
http://www.usbr.gov/uc/water/crsp/studies/24Month_09.pdf
Updated elevation projections for Lake Powell through water year 2010 based on the most recently published 24-Month Study are maintained at:
http://www.usbr.gov/uc/water/crsp/studies/lppwse.html
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%, July 95%. The overall estimated precipitation percentage of average thus far in water year 2010 for the Upper Colorado River Basin is 96% of average.
The Climate Prediction Center outlook (dated August 19, 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 August 10, 2010 the storage in Lake Powell was 15.36 million acre-feet (63.1 % of capacity) which is still below desired levels while the overall reservoir storage in the Colorado River Basin as of August 10, 2010 is 33.73 million acre-feet (56.7 % of capacity).
RRFW thanks Rick Clayton of the USBOR for his assistance in providing information for this notification.
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