Glen Canyon Dam Update

Glen Canyon Dam Lake Powell

During October 2010 the unregulated inflow volume to Lake Powell through
October 26, 2010 is tracking towards a monthly volume of was 330 thousand
acre feet (kaf) (60% of average). This volume will be below the volume
forecasted for October which was 375 kaf (69% of average). However, due to
significant local precipitation in the region around Lake Powell, the
elevation of Lake Powell will likely be about 0.7 feet above the level
projected in the October 24-Month Study for the end of October. The
elevation of Lake Powell on October 31, 2010 will likely be approximately
3633.75 feet above sea level which corresponds to a live storage of
approximately 15.30 maf and 62.9% of the full capacity of 24.32 million acre
feet (maf).

On November 1, 2010, the releases from Glen Canyon Dam will resume normal
fluctuations for power generations each day. During September and October
2010, the releases were steady with no fluctuations for power generation as
part of a 5 year study of steady flows pursuant to the February 2008 Finding
of No Significant Impact 'Experimental Releases from Glen Canyon Dam,
Arizona 2008 through 2012'. This was the third year of steady flows of the 5
year study. The steady release rate for this year was 8,000 cubic feet per
second (cfs). The volume released during September was 480 kaf and the
volume released in October will be approximately 495 kaf.

The release volume scheduled for November is 810 kaf which is equivalent to
an average daily release rate of approximately 13,600 cfs. Daily
fluctuations will likely peak near 16,000 cfs during the morning and
afternoon and evening hours. Daily low releases will occur during the early
morning hours (i.e. midnight to about 6:00 am) and will be about 8,000 cfs.
The projected release volume for December is currently 865 kaf which is
equivalent to an average daily release rate of approximately 14,050 cfs.
According to Bureau of Reclamation officials, the daily peak and low release
rate in December and January will likely also range from 16,000 cfs to 8,000
cfs respectively.

In addition to the daily fluctuation pattern for power generation, the
instantaneous releases from Glen Canyon Dam may also fluctuate somewhat to
provide approximately 40 megawatts of system regulation. These instantaneous
releases adjustments maintain stable conditions within the electrical
generation and transmission system and result in momentary release
fluctuations within a range that is about 1100 cfs above or below the
targeted release rate for a given hour of the day. These 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. When an unanticipated electrical outage event
occur within the electrical transmission system, this reserve generation at
Glen Canyon Dam can be called upon up to a limit of 83 megawatts
(approximately 2,250 cfs of release) for a duration of up to 2 hours. Under
normal circumstances, calls for reserve generation occur fairly infrequently
and are for much less than the limit of 83 megawatts.

In August of 2010, the August 2010 24-Month Study Model was used to project
the January 1, 2010 elevation of Lake Powell and Lake Mead under the most
probable inflow scenario. Pursuant to the Interim Guidelines and based on
this August projection, the operational tier for water year 2011 was
selected to be the Upper Elevation Balancing Tier. Under the Upper Elevation
Balancing Tier, there is a possibility that the annual release volume from
Lake Powell could be 8.23 maf. There is also a possibility under this tier
that Equalization or Balancing could occur in 2011 which would result in an
annual release volume greater than 8.23 maf.

The possibility of Equalization or Balancing in 2011 is dependent on the end
of water year 2011 reservoir conditions projected in the April 2011 24-Month
Study under the most probable inflow scenario and with 8.23 maf projected
for release from Lake Powell during water year 2011.  For this reason it
will not be known for certain whether Equalization or Balancing will occur
in water year 2011 until April 2011.  24-Month Studies prior to April 2011
can project that Equalization or Balancing are likely to occur, but these
projections are subject to change with changes in the forecasted hydrology
of the Colorado River Basin.  It is possible that a relatively small change
in forecasted hydrology can have a large impact on the projected annual
release volume.

The October 2010 24-Month Study with the most probable inflow and an 8.23
maf release does project that Balancing is likely to occur in 2011.   For
this reason, the projected most probable annual release volume for water
year 2011 in the October 24-Month Study is 9.00 maf. Given the current range
of uncertainty of the forecasted hydrology for water year 2011, it is
possible that Equalization could occur in water year 2011 which would result
if the annual release being greater than 10.7 maf.  Analysis of the probable
range of inflows that could occur during water year 2011 indicate that the
probability of Equalization occurring in 2011 is currently about 50%.

The current inflow forecast for Lake Powell projects the most probable
unregulated inflow volumes for the next 3 months as follows: October-375 kaf
(69% of average; November-400 kaf (73% of average); December-375 kaf (86% of
average). The outlook for water year 2011 (dated October 3, 2010) projected
the most probable unregulated inflow volume to Lake Powell during water year
2011 to be 9.60 maf (80% of average). It is possible that the unregulated
volume of inflow to Lake Powell in water year 2011 will be greater than or
less than the most probable projection. The probable range of unregulated
inflow volumes to Lake Powell during water year 2011 is currently projected
to be as dry as 4.5 maf (37% of average) to as wet as 15.8 maf (131% of

The October 2010 24-Month Study has been published and is available here:

The November 2010 24-Month Study will be published by November 10, 2010.
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

In the Upper Colorado River Basin during water year 2010, the overall
precipitation accumulated through September 30, 2009 was approximately 90%
of average based on the 30 year average for the period from 1971 through
2000. For October 2010, the first month of water year 2011, precipitation in
the Upper Colorado River Basin has been above normal and as of October 26th
is 170% of average.

The Climate Prediction Center outlook (dated October 21, 2010) for
temperature over the next 3 months indicates that temperatures in the Upper
Colorado River Basin are expected to be above average while precipitation
over the next 3 months is projected to be near 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 October 26, 2010 the storage in Lake Powell was 15.32
million acre-feet (63.0 % of capacity) which is still below desired levels
while the overall reservoir storage in the Colorado River Basin as of
October 26, 2010 is 32.84 million acre-feet (55.2 % of capacity).

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


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