Glen Canyon Dam Update April 2010

Glen Canyon Dam / Lake Powell

The unregulated inflow volume into Lake Powell in March was 475,000 acre-feet (72% of average). This was 25,000 acre-feet above the level forecasted in the March (Most Probable) 24-Month Study. The current elevation of Lake Powell as of April 8, 2010 is 3618.94 feet above sea level and stable. Inflows to Lake Powell are projected to increase during late April and into May and the reservoir elevation will likely begin to rise during this time. The April (Most Probable) 24-Month Study is projecting that the reservoir elevation will peak later this summer at approximately 3631 feet above sea level which is 69 feet from the full pool elevation of 3700 feet.

Releases from Glen Canyon Dam during the month of April will fluctuate each day for power generation between a peak hourly average release of about 12,500 cfs, during the morning and afternoon and a daily low hourly average release of 6,500 cfs during the late evening and early morning hours. The release volume scheduled for April is 600,000 acre-feet. The release volume projected for May is also 600,000 acre-feet and daily fluctuations in May will likely be very similar to April.

In addition to the daily fluctuation pattern, instantaneous releases from Glen Canyon Dam also fluctuate to provide approximately 40 megawatts 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 88 megawatts (approximately 2400 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 88 megawatts.

The snowpack conditions in the Upper Colorado River Basin are approximately 88% of average as of April 9, 2010. Typically the snowpack for the Upper Colorado River Basin peaks during the second week of April and begins to decline as temperatures increase and snowmelt begins. The Colorado Basin River Forecast Center (CBRFC) has issued the April Official Water Supply Forecast (April-July Unregulated Inflow Volume) for Lake Powell and it is projecting that the volume of unregulated inflow to Lake Powell for the period from April 1, 2010 through July 31, 2010 will be 5.0 million acre-feet (maf) which is 63% of average for the historic period from 1971-2000.

Based on the April Official Forecast, and a projected Lake Powell release volume of 8.23 maf pursuant to the Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lakes Powell and Mead (Interim Guidelines), the April (Most Probable) 24-Month Study projects that the water year ending elevation of Lake Powell will be 3629.20. This elevation is 12.8 feet below the Equalization Level for water year 2010 as established in the Interim Guidelines. This condition does not meet the criteria for an April adjustment to the Equalization Tier from the remainder of water year 2010 (see Section 6.B.3 of the Record of Decision ). Therefore, the release volume for water year 2010 will be 8.23 maf and monthly release volume for the remainder of the water year will be scheduled to meet this annual release volume.

The April 2010 24-Month Study will be published on April 10, 2010 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: Lake Powell Projected Elevations.

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 the 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 85%.

The Climate Prediction Center outlook (dated March 18, 2010) for temperature over the next 3 months indicates that temperatures in the Upper Colorado River Basin are expected to be above average and precipitation over the next 3 months in the Upper Colorado River Basin is projected to also be above 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 April 8, 2010 the storage in Lake Powell was 13.65 million acre-feet (56.1 percent of capacity) which is still below desired levels while the overall reservoir storage in the Colorado River Basin as of March 23, 2010 is 32.60 million acre-feet (54.8 percent of capacity).

This release courtesy Rick Clayton, US Bureau of Reclamation