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Old 04-08-2011   #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
April 8, 2011

Glen Canyon Dam / Lake Powell

The unregulated inflow to Lake Powell for March 2011 was 594 kaf (90% of
average). Observed inflows to Lake Powell have increased over the past
several weeks and are currently averaging about 10,400 cfs. With daily
average release rate from Glen Canyon Dam that is about 16,000 cfs, the
elevation of Lake Powell is still declining , but the rate of decline has
been moderated by these increased inflow conditions. The elevation of Lake
Powell at midnight on April 7, 2011 was 3609.84 feet above sea level (90.16
feet from full pool). The elevation of Lake Powell will begin to increase
later in April when inflows exceed releases. It is projected that the
elevation of Lake Powell could increase by more than 30 feet to a peak
elevation of approximately 3643 feet above sea level by late July or early

Current Dam Operations

The release volume scheduled for April is 966 kaf. During the first 3 days
of April, daily releases fluctuates for power production between an
afternoon peak of approximately 19,600 cfs and an early morning low release
of approximately 14,000 cfs. On April 4, 2011, Glen Canyon Powerplant Units
3 and 4 were taken out of service for approximately 6 weeks for annual
maintenance. Releases from Glen Canyon Dam were set to 16,000 cfs with no
fluctuations for power generation at that time due to limited capacity of
the available generating units at Glen Canyon Power Plant. Releases of
16,000 cfs steady will likely continue until the end of April. In early May,
releases will likely be steady at about 15,000 cfs for the first 13 days of
the month. On May 14, 2011 it is projected that Units 3 and 4 will be
returned to service. When this occurs, releases from Glen Canyon Dam will be
increased such that peak releases will be about 22,000 cfs and off peak
releases will be about 16,000 cfs. The projected release volume for May is
approximately 1.10 maf.

In addition to daily operations that may or may not include daily
fluctuation patterns for load following 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 can also occur
at Glen Canyon Dam. When an unanticipated electrical outage event occurs
within the electrical transmission system, reserve generation at Glen Canyon
Dam can be called upon up to a maximum 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 required 98 megawatts.

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 model projected the January 1, 2010
elevation of Lake Powell and Lake Mead under the most probable inflow
scenario. 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) and based on this August
projection, the operational tier for water year 2011 was selected to be the
Upper Elevation Balancing Tier. Under this operational tier, there is a
possibility that the annual release volume from Lake Powell could be as low
as 8.23 maf and there is also a possibility under this tier that
Equalization or Balancing could occur which would result in an annual
release volume greater than 8.23 maf.

The possibility of Equalization or Balancing in water year 2011 is dependent
upon the reservoir conditions of Lake Powell and Lake Mead projected at the
end of the water year in the Most Probable April 24-Month Study when the
projected Glen Canyon Dam annual release condition is 8.23 maf . The April
24-Month Study, with a projected water year release of 8.23 maf projects the
elevation of Lake Powell on September 30, 2011 (end of water year 2011) to
be 3662.63 feet above sea level which is above the Equalization Level for
2011 (3643 feet). Based on this model projection and consistent with the
Interim Guidelines, the Equalization Tier will govern the operation of Lake
Powell for the remainder of water year 2011.

Current Inflow Forecasts and Model Projections

Snowpack conditions above Lake Powell have persisted to be above average
since late December 2010. The overall snowpack above Lake Powell on April 7,
2011 was 115% of average. The current Water Supply forecast for Lake Powell
(April through July Unregulated Inflow Volume) is 9.5 maf (120% of average)
and this forecast was issued by the CBRFC on April 4, 2011.

The unregulated inflow forecast for Lake Powell over the next 3 months is as
follows: April-1,100 kaf (112% of average); May-3,000 kaf (130% of average);
June-3,850 kaf (125% of average). Incorporating these new forecasts with the
current Water Supply forecast, the projected unregulated inflow volume to
Lake Powell during water year 2011 is now 13.11 maf (109% of average). These
forecasts combined with projected inflows in August and September of 2011
make up the 2011 Most Probable water year inflow condition. The Most
Probable inflow condition has a statistical probability of being achieved
that is 50%. In other words, there is a 50% chance that the unregulated
inflow volume for water year 2011 for Lake Powell will be 13.11 maf or

A Minimum Probable water year inflow conditions has also been developed for
water year 2011. The Minimum Probable inflow condition has a statistical
probability of being achieved that is 90%. The 2011 Minimum Probable water
year inflow condition is currently 10.5 maf (87% of average). A Maximum
Probable water year inflow condition has also been developed for water year
2011. The 2011 Maximum Probable inflow condition is currently 16.2 maf (135%
of average).

The April 2011 24-Month Study, with the 2011 Most Probable inflow condition
projects that Equalization will be required under the Interim Guidelines and
the projected annual release volume is projected to be 11.56 maf. As
hydrologic conditions change during the remainder of the water year, this
annual release projection will be adjusted to achieve the Equalization Tier
of the Interim Guidelines.

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 - 225%, January
- 50%, February - 100%, March- 90%)

The Climate Prediction Center outlook (dated March 17, 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 in the northern reaches of the
basin while below average in the southern reaches of the basin.

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 April 7, 2011 the storage in Lake Powell was
approximately 12.71 million acre-feet (52.2 % of capacity) which is below
desired levels. The overall reservoir storage in the Colorado River Basin as
of April 7, 2011 is approximately 31.42 million acre-feet (52.8 % of

RRFW thanks Rick Clayton, US Bureau of Reclamation for this update.

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