Glen Canyon Dam Lake Powell During September 2010 through September 26, 2010 the unregulated inflow volume to Lake Powell is trending towards 266 thousand acre feet (kaf) (56% of average). This will be approximately 144 kaf below what was projected in the September 24-Month Study and as a result the elevation of Lake Powell at the end of September will be about 1 foot lower than what was projected in the September 24-Month Study. The September 30th elevation of Lake Powell will likely be approximately 3633.7 feet above sea level. This projected ending elevation corresponds to a live storage of 15.27 million acre feet (maf) which is 62.8% of the full capacity of 24.32 maf. During August the release volume from Glen Canyon Dam was 801.7 kaf and the hourly releases during most days fluctuated 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 for power generation. 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 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. The August 2010 24-Month Study (most probable inflow scenario) projected the January 1, 2011 elevation of Lake Powell to be 3628.73 feet. Pursuant to the Interim Guidelines, the determination is that the Operational Tier for water year 2011 will be the Upper Elevation Balancing Tier. Under this Operational Tier, there is a possibility that the annual release volume from Lake Powell could be 8.23 maf. There is also a possibility that Equalization or Balancing could occur in 2011 which would result in an annual release volume greater than 8.23 maf. The possibility of Equalization or Balancing in 2011 will depend on the reservoir conditions projected for the end of water year 2011 in the April 2011 24-Month Study with the most probable inflow scenario and 8.23 maf projected for release from Lake Powell. The September 2010 24-Month Study indicates that Equalization is likely to be triggered in April 2011 and the annual release volume for water year 2011 is projected to be 11.28 maf. There is a high level of uncertainty regarding the hydrologic conditions that will be experienced in water year 2011. Each month, the 24-Month Study will be updated to reflect current reservoir conditions and the most probable inflow forecast. The projected annual release volume for water year 2011 in the 24-Month Study will reflect the implementation of the Upper Elevation Balancing Tier with updated hydrologic conditions and is therefore likely to change each month. It is possible that a relatively small change in the forecast could have a large impact on the projected annual release volume. Based on the current inflow forecast (dated September 1, 2010), there is approximately a 58% probability that Equalization will occur in water year 2011. The current inflow forecast 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 outlook for water year 2011 (dated August 3, 2010) projected the most probable unregulated inflow volume to Lake Powell during water year 2011 to be 10.75 maf (89% of average). It is likely the unregulated volume of inflow to Lake Powell in water year 2011 will be greater than or less than the most probable projection. The range of possible unregulated inflow volumes to Lake Powell is currently projected to be as dry as 5.0 maf (40% of average) to as wet as 17.1 maf (142% of average). In October, this hydrologic outlook for water year 2011 will be updated. The September 2010 24-Month Study has been published and is 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 maf, 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 maf (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 September 1, 2010 the storage in Lake Powell was 15.36 maf (63.1 % of capacity) which is still below desired levels while the overall reservoir storage in the Colorado River Basin as of September 1, 2010 is 33.73 maf (56.7 % of capacity). RRFW thanks Rick Clayton of the USBOR for his assistance in providing information for this notification. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ RIVERWIRE is a free service to the community of river lovers from River Runners for Wilderness. To join, send an e-mail address to riverwire@rrfw.org and we'll add it to the RRFW RIVERWIRE e-mail alerts list. Join RRFW's listserver to stay abreast of and participate in the latest river issues. 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