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RRFW Riverwire - Glen Canyon Dam Update
July 23, 2010

Glen Canyon Dam Lake Powell

The unregulated inflow volume into Lake Powell for July 2010 through July
21st is 550 thousand acre feet (kaf) and at the current inflow rate, the
inflow volume for July 2010 will likely be approximately 674 kaf (43% of
average). Observed inflows peaked for water year 2010 on June 12, 2010 at
57,600 cubic feet per second (cfs). Since that time inflows have steadily
declined and as of July 21, 2010 inflows had decreased to 6,250 cfs. The low
water surface elevation for water year 2010 occurred on April 15, 2010 when
the elevation dipped to 3618.64 feet above sea level. Since that date the
elevation has been on the rise and reached a peak of 3638.82 on June 30,
2010. This will likely be the peak elevation for water year 2010 as inflows
are projected to fall below release rates during the next week. The overall
elevation increase for water year 2010 was just over 20 feet. By the end of
water year 2010 the elevation is projected to be roughly 3634.7 feet above
sea level. The April through July forecasted unregulated inflow to Lake
Powell is currently 5.77 maf (73% of average) based on the July midmonth

Releases from Glen Canyon Dam during the month of July will fluctuate each
day for power generation between a peak hourly average release of about
16,500 cfs, during the morning and afternoon and a daily low hourly average
release of 8,500 cfs during the late evening and early morning hours. The
release volume scheduled for July is 800,000 acre-feet. The release volume
for August will be approximately 800,000 acre-feet.

Bureau of Reclamation officials are projecting August flows to be the same
as July flows at this time, between a peak hourly average release of about
16,500 cfs, during the morning and afternoon and a daily low hourly average
release of 8,500 cfs during the late evening and early morning hours.

In addition to the daily fluctuation pattern, instantaneous releases from
Glen Canyon Dam also fluctuate to provide approximately 40 megawatts
(approximately 1,100 cfs) 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 83
megawatts (approximately 2,250 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 83 megawatts.

On September 1, 2010 and continuing through October 31, 2010, the releases
from Glen Canyon Dam will be steady with no fluctuations for power
production (excluding system regulation and spinning reserves) for a steady
flow experiment pursuant to the February 2008 Finding of No Significant
Impact 'Experimental Releases from Glen Canyon Dam, Arizona 2008 through
2012'. This year will be the third year of steady flows of the 5 year
experiment. The projected release rate being targeted is 8,000 cfs which is
equivalent to a monthly release volume of approximately 476,000 acre-feet in
September 2010 and 492,000 acre-feet in October 2010. At the end of August,
for a period of approximately 3 days, the daily fluctuation schedule will
change each day in order to gradually transition to the steady release rate
of 8,000 cfs to begin on September 1, 2010.

Pursuant to the Colorado River Interim Guidelines for Lower Basin Shortages
and Coordinated Operations for Lakes Powell and Mead (Interim Guidelines)
the operational tier for water year 2010 is Upper Elevation Balancing and
the projected water year release volume is 8.23 million acre feet (maf).
Under this operational tier there was a possibility that Equalization could
occur in 2010 if the April 2010 24-Month Study,with 8.23 maf projected for
release during water year 2010, indicated a Lake Powell projected elevation
on September 30 , 2010 greater than 3642 feet above sea level (the
Equalization level for water year 2010). This condition was not projected in
the April 24-Month Study and for this reason, the release volume for water
year 2010 will be 8.23 maf. Monthly release volumes for the remainder of the
water year will be scheduled to achieve this water year release volume.

The July 2010 24-Month Study projects that operation tier for Glen Canyon
Dam in water year 2011 will be Upper Elevation Balancing but also projects a
shift to Equalization in April 2011. The projected water year 2011 release
volume is 11.5 maf. It should be cautioned however that at this time of
year, the inflow assumptions used in the 24-Month Study for the following
water year are based on statistical averages and do not reflect current
hydrologic conditions. There is a high level of uncertainty about what the
inflow conditions will be in water year 2011. In August 2010 the Colorado
Basin River Forecast Center will issue an inflow projection for water year
2011 and this will be the basis of the inflow assumptions used in the August
2010 24-Month Study. It is currently forecasted that there is approximately
a 59% probability that Equalization will occur in water year 2011. This
forecast will be updated each month as conditions change.

The July 2010 24-Month Study has been published and will be available here:

Updated elevation projections for Lake Powell through water year 2010 based
on the most recently published 24-Month Study are maintained at:

Bureau of Reclamation - Upper Colorado Region Water Operations: 24-Month Study Reports

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 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%
and February 100%, March 90%, April 120%, May 75%, June 100%, . The overall
estimated precipitation percentage of average thus far in water year 2010
for the Upper Colorado River Basin is 87% of average.

The Climate Prediction Center outlook (dated July 15, 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 below 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 July 21, 2010 the storage in Lake Powell was 15.73
million acre-feet (64.7 % of capacity) which is still below desired levels
while the overall reservoir storage in the Colorado River Basin as of June
30, 2010 is 34.37 million acre-feet (57.8 % of capacity).

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