Glen Canyon Dam Update June 2012

Current Dam Operations

Releases from Glen Canyon Dam are now averaging about 12,600 cubic feet per second (cfs) with fluctuations for power generation throughout the day that peak near 15,000 cfs in the afternoons and with early morning low level releases are about 9,000 cfs and this operation is consistent with the Glen Canyon Operating Criteria (Federal Register, Volume 62, No. 41, March 3, 1997). The release volume for June is scheduled to be 708 kaf. In July, the monthly release volume will likely be about 889 kaf. Release fluctuations in July are projected to be in the range from about 10,000 cfs during the early morning hours to an afternoon peak of about 18,000 cfs.

The Water Supply Forecast for Lake Powell (April through July Unregulated Inflow Volume) has been updated for June and the forecasted unregulated inflow volume for the period from April through July for Lake Powell is now 2.01 million acre feet (maf) (28% of average). This is the third driest June forecast for Lake Powell since these forecasts began to be issued. Only 1977 and 2002 had lower June forecasts and these years ultimately were the 2 driest water years in the historic record for Lake Powell (1963-2011).

The monthly unregulated inflow volume to Lake Powell for May was 792 thousand acre-feet (kaf) (34% of average). This was 142 kaf above what was forecasted in early May. The release volume from Glen Canyon Dam in May was 601 kaf which was 1,000 acre-feet above what was scheduled for release during the month. As a result of the difference between the projections made in early May and actual conditions and operations that occurred in May, the elevation of Lake Powell at the end of May was 1.10 feet higher than projected. On May 31, 2012 the elevation of Lake Powell was 3636.83 feet above sea level (63.17 feet below full pool).

In addition to daily scheduled fluctuations for power generation, the instantaneous releases from Glen Canyon Dam may also fluctuate to provide 40 Megawatts (MW) of system regulation. These instantaneous release adjustments stabilize the electrical generation and transmission system and translate to a range of about 1100 cfs above or below the hourly scheduled release rate. Typically, fluctuations for system regulation are very short lived and balance out over the hour and do not have noticeable impacts on downstream river flow conditions.

Releases from Glen Canyon Dam can also fluctuate beyond scheduled fluctuations for power generation when called upon as a partner that shares reserve requirements within the electrical generator community (i.e. balancing area). There are many generators that supply electricity to the transmission system within the balancing area. At times, a participating generator may experience operating conditions such that it cannot make its scheduled delivery of electricity to the system (i.e. unscheduled outage). To provide system reliability, all participating electricity generators within the balancing area maintain a specified level of generation capacity (i.e. reserves) that can be called upon when an unscheduled outage occurs. Glen Canyon Dam typically maintains 113 MW of reserves for this purpose.

Reserve agreements allow the controllers of the balancing area to call upon Glen Canyon Dam to produce up to an additional 113 MW of electricity beyond what is originally scheduled for a given hour. Reserve calls can be maintained for a maximum of 2 hours after which time the generation rate should be returned to the original schedule. The 113 MW reserve requirement for Glen Canyon Dam translates to approximately 2,800 cfs of flow in the river. When the balancing area controllers call for reserve generation from Glen Canyon Dam, releases from the dam can exceed scheduled levels and have a noticeable impact on the river downstream from Glen Canyon Dam. But these calls for reserves are fairly infrequent and typically are for much less than the required level of 113 MW.

In August 2011, pursuant to the Interim Guidelines, the Operating Tier for Glen Canyon Dam was established to be the Equalization Tier. Under the Equalization Tier when conditions dry out as they have this year, the minimum annual release from Lake Powell can generally be as low as 8.23 maf. However, water year 2011 was a very wet Equalization year and not all of the Equalization release volume for 2011 could be achieved by September 30, 2011. As a result, 1.233 maf of the 2011 Equalization release volume was actually released after the end of water year 2011. This increased the minimum release volume for water year 2012 under Equalization to 9.463 maf. Under the dry hydrologic conditions currently projected for Lake Powell, the water year 2012 release volume is projected to be at this minimum Equalization level of 9.463 maf. As hydrologic conditions for Lake Powell and Lake Mead change throughout the year, Reclamation will adjust operations of Glen Canyon Dam to release the appropriate annual volume during 2012 to achieve Equalization objectives as practicably as possible by September 30, 2012.

Current Inflow Forecasts and Model Projections

Over the next three months (June, July and August) the forecasted unregulated inflow volume to Lake Powell is projected to be 350 kaf (13% of average), 100 kaf (9% of average) and 150 kaf (30% of average), respectively. These percent of averages are all based on the historic period from 1981 through 2010. The most probable (i.e. 50% likely to be exceeded) unregulated inflow volume for WY2012 is projected to be 5.01 maf (46% of average). Comparing this projected water year unregulated inflow volume to the driest year on record (2002) in which the unregulated inflow volume was only 2.64 maf (24% of average), water year 2012 will likely be very dry, yet not nearly as dry as conditions were in 2002. The currently projected water year unregulated inflow volume of 5.01 maf would rank as the 3rd driest year on record since the closure of Glen Canyon Dam (1963).

The annual release volume from Glen Canyon Dam will likely be 9.463 maf and the elevation of Lake Powell at the end of WY2012 is projected to be 3621.3 feet above sea level. This elevation corresponds to a live storage volume of 13.90 maf (57 % of full capacity). These projections are based on conditions in the June 24-Months Study.

Upper Colorado River Basin Hydrology

Since water year 2005, hydrologic conditions in the Upper Colorado River Basin have been near average with significant variability from year to year. The unregulated inflow to Lake Powell, which is a good measure of the hydrologic condition in the Colorado River Basin, has averaged a water year volume of 10.98 maf (101% of average (period 1981-2010)) during the period from 2005 through 2011. The hydrologic variability during this period has been from a low water year unregulated inflow volume of 8.62 maf (80% of average) in water year 2006 to a high water year unregulated inflow volume of 15.97 maf (147% of average) which occurred in water year 2011.

Overall reservoir storage in the Colorado River Basin has increased by over 8 maf since the beginning of water year 2005 and this is a significant improvement over the drought conditions during water years 2000 through 2004. On October 1, 2004, the beginning of water year 2005, the total reservoir storage in the Colorado River Basin was 29.84 maf (50.2% of capacity). On October 1, 2011, the beginning of water year 2012, the total reservoir storage in the Colorado River Basin was 38.66 maf (64.8% of capacity). As of June 12, 2012 the total reservoir storage in the Colorado River Basin was 36.59 maf (61.4% of capacity).