I get the Riverwire update emails about Glen Canyon Dam. This should clear up any questions:
RRFW Riverwire Glen Canyon Dam Update
July 8, 2011
Glen Canyon Dam Lake Powell
The unregulated inflow volume to Lake Powell for June 2011 was 5.40 maf
(175% of average). This was below the forecasted volume for June, which was
6.1 maf (198% of average) but was still the third wettest June on record
since the closure of Glen Canyon Dam. The observed inflow to Lake Powell
peaked on June 11th and 12th at just over 96,000 cfs. Inflows are now
declining but are still averaging about 80,000 cfs (as of July 5, 2011). The
forecasted unregulated inflow volume for July was increased from 3.30 maf to
3.53 maf (226% of average) which would be the 3rd wettest July for Lake
Powell since the operation of Glen Canyon Dam began in 1963.
The reservoir elevation of Lake Powell has increased significantly so far
this runoff season. On April 9, 2011 the elevation of Lake Powell was 3609.7
feet above sea level which was the lowest elevation observed so far in 2011.
Since that time the elevation of Lake Powell has increased by 42.7 feet to
3652.4 feet on July 5, 2011. The elevation is projected to continue to rise
and should peak near 3660 by the end of July. The last time Lake Powell's
reservoir elevation was at this level was in October of 2001 (over 10 years
ago) near the beginning of the recent drought.
Current Dam Operations
Releases from Glen Canyon Dam are approximately 24,400 cfs which is very
near the full capacity of the powerplant. This release rate includes
reserving enough generation capacity for up to 100 MW of reserve generation
and 40 MW of system regulation. As the elevation of Lake Powell increases,
the capacity of the powerplant will change and operation of Glen Canyon Dam
will be adjusted daily to maximize release volumes. It is anticipated that
the release volume for July will be approximately 1,465 kaf. The actual
release volume for July will largely depend on generation unit efficiencies
that occur throughout the month and could be higher or lower than this
estimated release volume.
While the release rate over the next several months is likely to be steady,
the instantaneous releases from Glen Canyon Dam may fluctuate somewhat to
provide 40 MW of system regulation. These instantaneous release adjustments
maintain stable conditions within the electrical generation and transmission
system and result in momentary release fluctuations within a range of about
1100 cfs above or below the targeted hourly release rate. The momentary
fluctuations for regulation are very short lived and typically balance out
over the hour.
Spinning and non-spinning reserve generation is also maintained at Glen
Canyon Dam. In order for Colorado River Storage Project (CRSP) powerplants
to participate in the electrical generation and transmissions system, these
powerplants must maintain a level of generation capacity available in
reserve to assist the local control area for when unanticipated generation
outages occur. The current CRSP powerplant reserve requirement is 100 MW
(equivalent to approximately 2,675 cfs of release from Glen Canyon Dam).
When an electrical outage occurs within the control area, CRSP powerplants
can be called upon to provide up to 100 MW of additional generation for up
to 2 hours. Under normal circumstances, calls for reserves infrequent and
for much less than the required 100 MW. Because Glen Canyon Powerplant is
the largest facility of the CRSP powerplants, most of the CRSP reserve
requirement is maintained at Glen Canyon Dam.
Annual Operations-Coordinated Operation of Lake Mead and Lake Powell under
Interim Guidelines for Water Year 2011
In August of 2010, the 24-Month Study was used to project the January 1,
2010 elevations of Lake Powell and Lake Mead. Based on these projected
elevations and pursuant to the December 2007 Record of Decision on Colorado
River Interim Guidelines for Lower Basin Shortages and the Coordinated
Operations of Lake Powell and Lake Mead (Interim Guidelines), the operating
tier for water year 2011 was selected to be Upper Elevation Balancing.
Operation of Glen Canyon Dam under Upper Elevation Balancing can result in
annual releases as low as 7.0 maf to as high as 13 maf or greater depending
on system conditions. The operational outcome of the Upper Elevation
Balancing Tier is largely dependent on system conditions at the end of the
water year that are projected in the April 24-Month Study.
The April 2011 24-Month Study projected the end of water year elevation for
Lake Powell would be above 3643 feet which is the Equalization Level for
2011. For this reason, pursuant to the Interim Guidelines, Equalization
will govern the operation of Glen Canyon Dam for the remaining months of
water year 2011. For more information on the Interim Guidelines click
http://www.usbr.gov/lc/region/programs/ ... cision.pdf
Current Inflow Forecasts and Model Projections
The Water Supply forecast for Lake Powell (April through July Unregulated
Inflow Volume) is 12.0 maf (151% of average) and the water year unregulated
inflow to Powell for 2011 is projected to be 16.2 maf (135% of average).
The unregulated inflow forecasts for Lake Powell over the next 3 months are
as follows: July-3,530 kaf (226% of average); August-950 kaf (155% of
average): September-670 kaf (141% of average). These forecasts were last
updated on July 1, 2011. Incorporating these new forecasts, the projected
most probable unregulated inflow for water year 2011 is now 16.2 maf (131%
of average). This is the median projection for water year 2011. There is a
50% chance that the actual volume could be higher and there is a 50% the
actual volume could be lower than this projected volume.
The June 24-Month Study projects a Lake Powell WY 2011 annual release volume
of 12.44 maf. Due to recent increases to the inflow forecast for Lake
Powell, Equalization may not be fully achieved by the end of the water year.
The projected Lake Powell releases will be updated each month to reflect
changing hydrology in order to achieve the operation specified by the
The July 2011 24-Month Study will published on July 8, 2011 and will be
available here: http://www.usbr.gov/uc/water/crsp/studi ... nth_07.pdf
Updated elevation projections for Lake Powell through water year 2011 and
2012 based on the most recently published 24-Month Study are maintained at:
Upper Colorado River Basin Hydrology
The Upper Colorado River Basin has experienced a protracted multi-year
drought since early 2000. During this drought, the inflows to Lake Powell
have been below average in every year except water years 2005, 2008 and
likely 2011. 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 near or
above average inflow conditions and net gains in storage to Lake Powell.
This year (2011) will likely be another above average inflow year. As of
July 5, 2011 the storage in Lake Powell was approximately 17.52 million
acre-feet (72.0 % of capacity) which is still below the desired operating
level for this time of year. The overall reservoir storage in the Colorado
River Basin as of July 5, 2011 is approximately 37.48 million acre-feet
(63.0 % of capacity).
RRFW thanks Rick Clayton of the USBOR for this information.