RRFW Riverwire Glen Canyon Dam Update - Mountain Buzz
 



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Old 02-27-2010   #1
 
Tom Martin's Avatar
 
Flagstaff, Arizona
Join Date: Dec 2004
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RRFW Riverwire Glen Canyon Dam Update

RRFW Riverwire Glen Canyon Dam Update
February 27, 2010

Glen Canyon Dam / Lake Powell

The unregulated inflow volume into Lake Powell so far in February has been somewhat below the forecasted level. As of February 21, 2010 the unregulated inflow rate to Lake Powell is on pace to reach approximately 295,000 acre-feet for the month which would be about 30,000 acre-feet less than what was forecasted at the beginning of February. The February 2010 24-Month Study projected that the end of month elevation of Lake Powell would be 3619.97 feet above sea level. As of February 21, 2010 the projected end of month elevation of Lake Powell is now 3620.19 feet above sea level (about 2 inches above what was projected) which is about 2 feet lower than the reservoir elevation on February 1, 2010.

Releases from Glen Canyon Dam during the month of February 2010 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.

For March, the release volume is projected to be 600,000 acre-feet. Daily fluctuations in March are projected to 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 mid-month Water Supply Forecast for February (April-July Unregulated Inflow Volume) was reduced by 200,000 acre-feet from the official Water Supply Forecast for February to 5.6 million acre-feet (maf) which is 71% of average. This forecast will be updated during the first week of March 2010.

The February 2010 24-Month Study projected 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 possible, if hydrologic conditions become wetter than what is currently projected, that an April adjustment to Equalization could occur. If this adjustment were to occur in April, the projected water year release from Glen Canyon Dam could be greater than 10.5 maf.

As of early February, 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 about a 25% probability that an April adjustment to Equalization 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 indication of the probability that Equalization will occur in water year 2010.

The February 2010 24-Month Study has been published and will be available
here:
http://www.usbr.gov/uc/water/crsp/studies/24Month_02.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%.

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 February 9, 2010 the storage in Lake Powell was 13.93 million acre-feet (57.29 percent of capacity) which is still below desired levels while the overall reservoir storage in the Colorado River Basin as of February 9, 2010 is 33.14 million acre-feet
(55.72 percent of capacity).

RRFW thanks Rick Clayton of the USBOR for his assistance in providing information for this notification.

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Old 02-28-2010   #2
 
sealion's Avatar
 
Moab, Utah
Paddling Since: 1987
Join Date: Oct 2008
Posts: 133
The "equalizing" or "balancing" releases- could either of those be a 40K release? or do they just up the flow a little more?
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Old 02-28-2010   #3
 
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Flagstaff, Arizona
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No, not a 40K flow, but monthly tweaks to the Dam release. It is snow pack linked, and the northern part of the river basin is dry right now. This could change if wetter weather shows up. Yours, tom
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