Glen Canyon Dam Lake Powell
The unregulated inflow volume to Lake Powell so far in July (as of July 28th) has been 4.15 million acre feet (maf). At the current rate the unregulated inflow volume for July will likely be approximately 4.33 maf which is 278% of average. This July volume will likely be the 2nd wettest July on record since the closure of Glen Canyon Dam (1963). Only 1995 had a wetter July than this year at 4.41 maf. The expected unregulated inflow volume for the April through July period is approximately 12.9 maf (162% of average).
The reservoir elevation of Lake Powell has increased significantly so far this runoff season. On April 9, 2011 the elevation of Lake Powell was 3609.7 feet above sea level which was the lowest elevation observed so far in 2011. Since that time the elevation of Lake Powell has increased by over 50 feet and on July 28, 2011 the reservoir elevation of Lake Powell was 3660.79 feet above sea level (39.21 feet from full pool). The last time Lake Powell’s reservoir elevation was at this level was in October of 2001 (over 10 years ago) near the beginning of the recent drought. The live storage of Lake Powell on July 28, 2011 was 18.60 maf which is 76% of capacity. The elevation of Lake Powell is very near the peak elevation that will occur this year. Inflows to Lake Powell are steadily declining and by early August will be less than the release rate at Glen Canyon Dam. When this occurs, the elevation will gradually begin to decline and this condition will continue through the fall and winter months.
Current Dam Operations
Releases from Glen Canyon Dam are approximately 24,100 cubic feet per second (cfs) which is very near the full capacity of the power plant. The release volume for July will likely be approximately 1.485 maf. Releases in August will be similar to July with releases projected to be approximately 24,000 cfs. On August 2nd, 1 unit at Glen Canyon Dam will be out of service from approximately 7:00 am to 4:00 pm for a short term maintenance project. This will reduce the release rate during this period to approximately 20,000 cfs. At the end of August, releases will likely be gradually reduced to approximately 15,000 cfs as a transition to the Steady Flow Experiment to be conducted during September and October of 2011. This year will be the 4th year of a 5 year study of steady flows during September and October as describe in the 2008 Environmental Assessment and Finding of No Significant Impact. The target release rate for the steady flow experiment this year is approximately 15,000 cfs depending on the available capacity of Glen Canyon Power Plant.
While the release rate over the next several months is likely to be steady, the instantaneous releases from Glen Canyon Dam may fluctuate somewhat to provide 40 Mega Watts (MW) of system regulation. These instantaneous release adjustments maintain stable conditions within the electrical generation and transmission system and result in momentary release fluctuations within a range of about 1100 cfs above or below the targeted hourly release rate. The momentary fluctuations for regulation are very short lived and typically balance out over the hour.
Spinning and non-spinning reserve generation is also maintained at Glen Canyon Dam. In order for Colorado River Storage Project (CRSP) power plants to participate in the electrical generation and transmissions system, these powerplants must maintain a level of generation capacity available in reserve to assist the local control area for when unanticipated generation outages occur. The current CRSP power plant reserve requirement is 100 MW (equivalent to approximately 2,675 cfs of release from Glen Canyon Dam). When an electrical outage occurs within the control area, CRSP power plants can be called upon to provide up to 100 MW of additional generation for up to 2 hours. Under normal circumstances, calls for reserves infrequent and for much less than the required 100 MW. Because Glen Canyon Power plant is the largest facility of the CRSP power plants, most of the CRSP reserve requirement is maintained at Glen Canyon Dam.
Annual Operations-Coordinated Operation of Lake Mead and Lake Powell under Interim Guidelines for Water Year 2011
In August of 2010, the 24-Month Study was used to project the January 1, 2010 elevations of Lake Powell and Lake Mead. Based on these projected elevations and pursuant to the December 2007 Record of Decision on Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations of Lake Powell and Lake Mead (Interim Guidelines), the operating tier for water year 2011 was selected to be Upper Elevation Balancing. Operation of Glen Canyon Dam under Upper Elevation Balancing can result in annual releases as low as 7.0 maf to as high as 13 maf or greater depending on system conditions. The operational outcome of the Upper Elevation Balancing Tier is largely dependent on system conditions at the end of the water year that are projected in the April 24-Month Study.
The April 2011 24-Month Study projected the end of water year elevation for Lake Powell would be above 3643 feet which is the Equalization Level for 2011. For this reason, pursuant to the Interim Guidelines, Equalization will govern the operation of Glen Canyon Dam for the remaining months of water year 2011. For more information on the Interim Guidelines click here:
http://www.usbr.gov/lc/region/programs/strategies/RecordofDecision.pdf
Current Inflow Forecasts and Model Projections
The Water Supply forecast for Lake Powell (April through July Unregulated Inflow Volume) is 12.0 maf (151% of average) and the water year unregulated inflow to Powell for 2011 is projected to be 16.2 maf (135% of average). The unregulated inflow forecasts for Lake Powell over the next 3 months are as follows: July-4,000 kaf (257% of average); August-1,000 kaf (162% of average): September-670 kaf (141% of average). These forecasts were last updated on July 15, 2011. Incorporating these new forecasts, the projected most probable unregulated inflow for water year 2011 is now 16.7 maf (139% of average). This is the median projection for water year 2011. There is a 50% chance that the actual volume could be higher and there is a 50% the actual volume could be lower than this projected volume.
The July 24-Month Study projected a Lake Powell WY 2011 annual release volume of 12.45 maf. Due to recent increases to the inflow forecast for Lake Powell, Equalization may not be fully achieved by the end of the water year. The projected Lake Powell releases will be updated each month to reflect changing hydrology in order to achieve the operation specified by the Equalization Tier.
The July 2011 24-Month Study has been published and will be available here:
http://www.usbr.gov/uc/water/crsp/studies/24Month_07.pdf
Updated elevation projections for Lake Powell through water year 2011 and 2012 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
The Upper Colorado River Basin has experienced a protracted multi-year drought since early 2000. During this drought, the inflows to Lake Powell have been below average in every year except water years 2005, 2008 and likely 2011. 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 near or above average inflow conditions and net gains in storage to Lake Powell. This year (2011) will likely be another above average inflow year. As of July 28, 2011 the storage in Lake Powell was approximately 18.60 million acre-feet (76.0 % of capacity) which is still below the desired operating level for this time of year. The overall reservoir storage in the Colorado River Basin as of July 28, 2011 is approximately 39.20 million acre-feet (65.9 % of capacity).
RRFW thanks Rick Clayton of the USBOR for this information.