Join Date: Dec 2004
RRFW Riverwire - Glen Canyon Dam Update
RRFW Riverwire - Glen Canyon Dam Update
February 7, 2010
Glen Canyon Dam and Lake Powell
The unregulated inflow volume into Lake Powell in January 2010 was just below what was forecasted at the beginning of January. The unregulated inflow to Lake Powell for the month of January was 304,000 acre-feet (75% of average). This was about 26,000 acre-feet below the unregulated inflow volume that was projected in the January 2010 24-Month Study. For this reason, the elevation of Lake Powell at the end of January was about 2 inches below what was projected in the January 2010 24-Month Study. The end of January Lake Powell elevation was 3622.12 feet above sea level which was over 4 feet lower than the elevation on January 1, 2010.
The release volume for January 2010 was 900,480 acre-feet. Daily peak releases for power generation in January were 17,500 cfs during the morning and afternoon with lows of approximately 9,500 cfs in the very early morning hours. In February 2010 the scheduled release volume for the month is 640,000 acre-feet. Peak releases each day for power generation in February will be approximately 14,000 cfs with lows of about 8,000 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. These momentary fluctuations for regulation are very short lived and typically balance out over the hour. Glen Canyon Dam also provides a level of reserve generation that can be called upon when unanticipated outages occur within the generation system. When an outage event occurs, reserve generation at Glen Canyon Dam can be called upon and this additional reserve generation is typically maintained for 2 hours or less.
The official Water Supply Forecast (April-July Unregulated Inflow Volume) for Lake Powell issued by the Colorado Basin River Forecast Center will be updated during the first week of February. The January official forecast for Lake Powell unregulated inflow was 6.2 million acre-feet (maf) which is 78% of average for the period from 1971 to 2000. The preliminary Water Supply Forecast updated for February has been released and is 6.0 maf (76% of average). The official Water Supply Forecast is expected to be released later this week.
Based on the January forecast, the January 2010 24-Month Study projected that the water year release volume from Lake Powell was likely to 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. It is possible, if hydrologic conditions become wetter than current levels, that an April adjustment to Equalization could occur and under Equalization the projected water year release from Glen Canyon Dam could be greater than 10.5 maf.
As of early January, given the hydrologic conditions within the Colorado River Basin and the range of possible inflow scenarios that could occur in 2010, Reclamation estimates that there is was about a 21% probability that an April adjustment to the Equalization Tier will occur. This estimate is based on many factors that are changing through time. Reclamation will update this estimated probability each month to provide stakeholders some probablistic estimate of the possibility that Equalization will occur in water year 2010.
The January 2010 24-Month Study has been published and is available here:
Updated elevation projections for Lake Powell through water year 2010 based on the most recently published 24-Month Study are maintained at:
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 continued. Precipitation for October 2009 was 85% of average and for November, precipitation was estimated to be only 40% of average. In December 2009, the estimated precipitation above Lake Powell was 115% of average.
The Climate Prediction Center outlook (dated January 21, 2010) for temperature over the next 3 months indicates that temperatures in the northern reaches of the Upper Colorado River Basin have an increased probability of being above average. Accumulated precipitation over the next 3 months are projected to be near average in the Upper Colorado River Basin (above Lake Powell) while are projected to be above average in the Lower Colorado River Basin (below Lake Powell).
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 January 31, 2010 the storage in Lake Powell was 13.99 million acre-feet (57.52 percent of capacity) which is still below desired levels while the overall reservoir storage in the Colorado River Basin as of January 31, 2010 is 33.01 million acre-feet (55.64 percent of capacity).
RRFW thanks Rick Clayton of the USBOR for his assistance in providing information for this notification.
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