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Old 01-11-2011   #1
Tom Martin's Avatar
Flagstaff, Arizona
Join Date: Dec 2004
Posts: 817
RRFW Riverwire - Glen Canyon Dam Update

RRFW Riverwire - Glen Canyon Dam Update
January 11, 2011

Glen Canyon Dam - Lake Powell

During December 2010 the unregulated inflow to Lake Powell was 417 thousand
acre feet (kaf) (96% of average). This was 57 kaf above the volume
forecasted by the Colorado Basin River Forecast Center (CBRFC) on December
1, 2010 which was 360 kaf (83% of average). The elevation of Lake Powell at
the end of the day on December 31, 2010 was 3626.54 feet above sea level
(73.46 feet from full pool) which corresponds to a live storage content of
14.44 maf (59.5% of capacity).

During the last half of December, precipitation within the Upper Colorado
River Basin was well above average and the snowpack conditions have
increased significantly. On December 17, 2010 the snowpack above Lake Powell
was estimated to be 102% of average. By December 31, 2010 the snowpack
conditions above Lake Powell had increased to an estimated 151% of average.
Precipitation above Lake Powell for the first 3 months of water year 2011
has been well above average at nearly 150% of average.

Based on these conditions and projected climate conditions over the next
several months, the CBRFC has issued the Final Water Supply Forecast (April
through July 2011 forecasted unregulated inflow volume) for Lake Powell that
is well above average at 9.5 million acre feet (maf) which is 120% of
average. This forecast translates into an increase to the expected inflow to
Lake Powell for water year 2011 that is more than 3 million acre-feet more
than what was projected one month ago.

Operation of Glen Canyon Dam during January 2011 has been modified based on
this new forecast. On Sunday January 9, 2011, releases from Glen Canyon Dam
were increased to an average daily release volume of approximately 34,000
acre-feet which translates to an average daily release of 17,100 cfs.
Releases are scheduled to peak for power generation during the afternoon
hours for the remainder of January to 20,500 cfs. Releases during the early
morning hours are approximately 12,500 cfs.

The release volume for February is projected to be 981,000 kaf which the
estimated capacity of Glen Canyon Power plant under the scheduled
maintenance unit outage plan with an allowance of capacity to provide
spinning reserves and regulation. It is anticipated that fluctuations for power generation will be minimal in February and the estimated release
rate will likely be approximately 17,600 cfs.

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 98 megawatts
(approximately 2,600 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 98 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
determined 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 January 2011 24-Month Study with the most probable inflow scenario for
water year 2011 projects that Equalization is likely to occur in 2011. For
this reason, the projected most probable annual release volume for water
year 2011 in the January 24-Month Study is 11.367 maf. Given the current
range of uncertainty of the forecasted hydrology for water year 2011, it is
possible that Balancing could also occur in water year 2011 which would
result if the annual release being 9.0 maf. Each month the 24-Month Study is
updated to reflect the most probable inflow scenario which is based on the
most recent forecast from the Colorado River Basin Forecast Center (CBRFC).
Analysis of the probable range of inflows that could occur during water year
2011 indicates that the probability of realizing an inflow volume that would
trigger Equalization in 2011 is currently about 76%. This probability will
be updated again during the first part of February 2011.

The unregulated inflow forecast for Lake Powell over the next 3 months is as
follows: January-380 kaf (94% of average); February-380 kaf (90% of
average); March-670 kaf (101% of average). The outlook for water year 2011,
incorporating this new forecast and the January Final Water Supply Forecast,
the most probable unregulated inflow volume to Lake Powell during water year
2011 is now 13.19 maf (110% 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 8.9 maf (74% of average) to as wet as 18.6 maf (154% of

Upper Colorado River Basin Hydrology

In the Upper Colorado River Basin during water year 2010, the overall
precipitation accumulated through September 30, 2010 was approximately 90%
of average based on the 30 year average for the period from 1971 through
2000. For Water Year 2011 thus far, the estimated monthly precipitation
within the Upper Colorado River Basin (above Lake Powell) as a percentage of
average has been: (October - 135%, November - 95%,December -230%).

The Climate Prediction Center outlook (dated December 16, 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 is also 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 January 10, 2011 the storage in Lake Powell was
approximately 14.26 million acre-feet (58.6 % of capacity) which is below
desired levels. The overall reservoir storage in the Colorado River Basin as
of January 10, 2011 is approximately 32.29 million acre-feet (54.3 % of

RRFW thanks Rick Clayton of the USBOR for this update.

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