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Old 12-14-2012, 01:27 PM
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Glen Canyon Dam / Lake Powell –Water Flows and Projections

Glen Canyon Dam / Lake Powell –
Recent Reservoir Operations
The unregulated inflow volume to Lake Powell in November was 246 thousand acre-feet
(kaf) (52% of average). The release volume from Glen Canyon Dam in November was
730 kaf. The end of November elevation and storage of Lake Powell were 3615.1 feet
(85 feet from full pool) and 13.25 maf (54% of full capacity). The reservoir elevation
will continue to decline through the fall and winter months.
From November 18-23, 2012, the Department of Interior conducted the first High Flow
Experiment under a multi-year High Flow Protocol announced earlier this year by
Secretary Salazar. Under this Protocol, high flow releases are linked to sediment input
and other resource conditions below Glen Canyon Dam. Beginning on the evening of
November 18th, releases from Glen Canyon Dam began ramping up to full power plant
capacity (approximately 28,000 cfs). At midday on November 19th, bypass tubes at Glen
Canyon Dam were opened and releases continued to increase up to full power plant and
bypass capacity (approximately 43,000 cfs) by the evening of November 19th. Releases
were maintained at peak release for 24 hours and then began ramping back down.
Releases returned to normal operations in the evening of November 23rd. The entire
experiment, including ramping lasted 5 days, with 24 hours at peak release. November
releases from Glen Canyon Dam prior to and after the High Flow Experiment fluctuated
between 7,000cfs and 9,000cfs. The elevation of Lake Powell decreased approximately
2.75 feet during the 5-day experiment. Approximately 77,800 acre-feet was bypassed
during the experiment. The total annual release from Glen Canyon Dam in water year
2013 will not change as a result of the High Flow Experiment.
Current and Planned Reservoir Operations
The operating tier for 2013 is the Upper Elevation Balancing Tier, as establish in August
2012 and pursuant to the Interim Guidelines. However, if hydrologic conditions and
projections become wetter, it is possible that beginning in April, the Equalization tier will
govern the operations of Lake Powell for the remainder of the water year. Based on
analysis of a range of inflow scenarios, however, the current probability of realizing an
inflow volume that would trigger Equalization in 2013 is less than 5 percent. As
hydrologic conditions for Lake Powell and Lake Mead change throughout the year,
Reclamation will adjust operations of Glen Canyon Dam to release the appropriate annual
volume during 2013 to achieve the governing operating tier objectives as practicably as
possible by September 30, 2013.
Releases from Glen Canyon Dam in December are currently averaging approximately
13,000 cfs with daily fluctuations between 8,250cfs and 16,250cfs and consistent with the
Glen Canyon Operating Criteria (Federal Register, Volume 62, No. 41, March 3, 1997).
The scheduled release volume for December 2012 is 800 kaf.
In January, the release volume will likely be about 800 kaf, with fluctuations throughout
the day from about 8,500 cfs in the early morning to about 16,500 cfs in the evening. In
February, the release volume will likely be about 600 kaf with daily fluctuations for
hydropower between approximately 8,000 cfs and 14,000 cfs.
In addition to daily scheduled fluctuations for power generation, the instantaneous
releases from Glen Canyon Dam may also fluctuate to provide 40 MW of system
regulation. These instantaneous release adjustments stabilize the electrical generation
and transmission system and translate to a range of about 1,100 cfs above or below the
hourly scheduled release rate. Typically, fluctuations for system regulation are very short
lived and balance out over the hour and do not have noticeable impacts on downstream
river flow conditions.
Releases from Glen Canyon Dam can also fluctuate beyond scheduled fluctuations for
power generation when called upon as a partner that shares reserve requirements within
the electrical generator community (i.e. balancing area). Reserves provide system
reliability in the event of an unscheduled outage. Glen Canyon Dam typically maintains
43 MW of reserves (approximately 1,100 cfs). Reserve calls can be maintained for a
maximum of 2 hours after which time the generation rate should be returned to the
original schedule. If reserves from Glen Canyon Dam are called upon, releases from the
dam can exceed scheduled levels and can have a noticeable impact on the river
downstream from Glen Canyon Dam. Calls for reserves are fairly infrequent and
typically are for much less than 43 MW.
Current Inflow Forecasts and Model Projections
The hydrologic forecast for Lake Powell for water year 2013 projects that the most
probable (median) unregulated inflow volume will be 5.76 maf (53% of average based on
the period 1981-2010). Based on this hydrologic outlook, the December 24-Month study
projects the annual release volume for water year 2013 will be 8.23 maf and the end of
water year reservoir elevation and storage for Lake Powell will be 3594.8 and 11.26 maf
(48% capacity), respectively.
If hydrologic conditions and projections become significantly wetter, it is possible that
beginning in April, the Equalization tier will govern the operations of Lake Powell for the
remainder of the water year and the release volume for 2013 could be greater than 8.23
maf. However, based on analysis of a range of inflow scenarios, the current probability
of realizing an inflow volume that would trigger Equalization in 2013 is less than 5
percent.
Upper Colorado River Basin Hydrology - Since water year 2005, the Upper Colorado
River Basin has experienced significant year to year hydrologic variability. The
unregulated inflow to Lake Powell, which is a good measure of hydrologic conditions in
the Colorado River Basin, has averaged a water year volume of 10.22 maf (94% of
average (period 1981-2010)) during the period from 2005 through 2012. The hydrologic
variability during this period has been from a low water year unregulated inflow volume
of 4.91 maf (45% of average) in water year 2012 to a high water year unregulated inflow
volume of 15.97 maf (147% of average) in water year 2011. Based on observed inflows
and current forecasts, water year 2013 unregulated inflow is expected to be 5.76 maf
(53% of average).
Overall reservoir storage in the Colorado River Basin has increased by over 4 maf since
the beginning of water year 2005 and this is an improvement over the persistent drought
conditions during water years 2000 through 2004. From the beginning of water year
2005 to the beginning of water year 2013, the total reservoir storage in the Colorado
River Basin increased from 29.8 maf (50% of capacity) to 33.9 maf (57 % of capacity).
However, this period experienced year to year increases and decreases in total Colorado
Basin storage in response to wet and dry hydrology.
Updated: December 12, 2012
Katrina Grantz
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