Glen Canyon Dam - Lake Powell
River Runners for Wilderness would like to inform river runners launching from Lee’s Ferry during the month of April 2010 that the projected daily fluctuation releases from Glen Canyon Dam in April will have a peak hourly average release each day of approximately 12,000 cubic feet per second and a daily low hourly average release of approximately 6,000 cfs. The Bureau of Reclamation notes this will result in a projected release volume for April of 600,000 acre-feet from Lake Powell.
The unregulated inflow volume into Lake Powell in February was 294,000 acre-feet (70% of average). This was 31,000 acre-feet below what was forecasted in the February 2010 24-Month Study. Despite this shortfall, the observed Lake Powell elevation at the end of February was about 3 inches higher than the what was projected in the February 24-Month Study. The end of February water surface elevation of Lake Powell was 3620.16 feet above sea level (79.84 feet from full pool). During the month of February, the elevation of Lake Powell declined by approximately 2 feet.
Releases from Glen Canyon Dam during the month of February have fluctuated each day for power generation between a peak hourly average release of about 14,000 cubic feet per second (cfs), during the morning and afternoon and a daily low hourly average release of 8,000 cfs during the late evening and early morning hours. The release volume for February was 630,500 acre-feet. For March, the release volume is scheduled to be 600,000 acre-feet. Daily fluctuations in March will have a peak hourly average release each day of approximately 12,000 cfs and a daily low hourly average release of approximately 6,000 cfs.
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 official Water Supply Forecast for March (April-July Unregulated Inflow Volume) is now 5.4 million acre feet (maf) (68% of average). Based on this forecast, the March 2010 24-Month Study projects that the water year release volume from Lake Powell will likely be 8.23 maf pursuant to the Interim Guidelines. However, the operating tier for Glen Canyon Dam in water year 2010 is Upper Elevation Balancing and under this tier there is a possibility for an April adjustment to the operational plan which could incorporate either Equalization releases or Balancing releases. Given the current conditions of Lake Powell and Lake Mead, it is remotely possible, if hydrologic conditions become wetter than what is currently projected, that an April adjustment to Equalization could occur which would require a water year release volume from Glen Canyon Dam on the order of approximately 10.5 maf.
Reclamation estimates that the official Water Supply Forecast for April would have to increase by approximately 1.2 maf above the level forecasted in March in order for an April Adjustment to the Equalization Tier to occur in water year 2010. Over the past 31 years, only once has the Water Supply Forecast increased by at least this volume from one month to the next. For this reason, Reclamation estimates that the probability of an April Adjustment to the Equalization Tier in water year 2010 to be only about 3 percent.
The March 2010 24-Month Study is available here: http://www.usbr.gov/uc/water/crsp/studies/24Month_03.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 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%.
The Climate Prediction Center outlook (dated February 18, 2010) for temperature over the next 3 months indicates that temperatures in the Upper Colorado River Basin are expected to be near average while precipitation over the next 3 months in the Upper Colorado River Basin is projected to 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 March 8, 2010 the storage in Lake Powell was 13.76 million acre-feet (56.6 percent of capacity) which is still below desired levels while the overall reservoir storage in the Colorado River Basin as of March 8, 2010 is 32.92 million acre-feet (55.4 percent of capacity).
RRFW thanks Rick Clayton of the USBOR for his assistance in providing information for this notification.
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