Dam Operations

Current Dam Operations


 

 

 

 

 

 

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Updated 2/25/14

 
Current Status

The unregulated inflow volume to Lake Powell in January was 270 thousand
acre-feet (kaf) (75% of average). The release volume from Glen Canyon Dam in
January was 800 kaf. The end of January elevation and storage of Lake Powell
were 3578.7 feet (121 feet from full pool) and 9.83 million acre-feet (maf)
(40% of full capacity), respectively. The reservoir elevation is now
declining and will continue to decline until spring runoff. Snowpack is
currently about 111% of median for this time of year.

Current Operations

In February, the release volume was about 600 kaf, with fluctuations from
about 8,000 cubic feet per second (cfs) in the nighttime to about 14,000 cfs
in the daytime and consistent with the Glen Canyon Operating Criteria
(Federal Register, Volume 62, No. 41, March 3, 1997).

Hourly releases during March 2014 are anticipated to fluctuate between
approximately 6,000 cfs in the nighttime and approximately 11,000 cfs in the
daytime. The Bureau of Reclamation anticipates the release volume for April
2014 will be approximately 500,000 acre-feet with fluctuations between
approximately 6,000 cfs and 11,000 cfs. The anticipated release volume for
May 2014 is about 510,000 acre feet with fluctuations between approximately
6,000 cfs and 11,000 cfs. This will be confirmed in a subsequent
notification toward the end of March.

In addition to daily scheduled fluctuations for power generation, the
instantaneous releases from Glen Canyon Dam may also fluctuate to provide 40
Megawats (MW) of system regulation. These instantaneous release adjustments
stabilize the electrical generation and transmission system and translate to
a range of about 1,200 cfs above or below the hourly scheduled release rate.
Under system normal conditions, fluctuations for regulation are typically
short lived and generally balance out over the hour with minimal or no
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 41 MW of reserves
(approximately 1,200 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 41 MW.

The operating tier for water year 2014 is the Mid-Elevation Release Tier
with an annual release volume of 7.48 maf, as established in August 2013 and
pursuant to the Interim Guidelines, Section 6.C.1. Reclamation will schedule
operations at Glen Canyon Dam to achieve as practicably as possible a 7.48
maf annual release by September 30, 2014.

Inflow Forecasts and Model Projections

The forecast for the 2014 April to July water supply season for Lake Powell,
issued on Feb 4th by the Colorado Basin River Forecast Center, projects that
the most probable (median) unregulated inflow volume will be 7.25 maf (101%
of average based on the period 1981-2010). The April-July forecast increased
by 440 kaf since last month. The winter snow accumulation season has tracked
near average so far (currently 111% of median), however we are currently
roughly two-thirds of the way through the snow accumulation season and there
is still uncertainty regarding the final snowpack and resulting runoff. The
April-July forecast ranges from a minimum probable of 4.75 maf (66% of
average) to a maximum probable of 10.3 maf (144% of average). (For
reference, the 30-year April-Juny average is 7.16 maf.) There is a 10
percent chance that inflows could be higher than the maximum probable and a
10 percent chance they could be lower than the minimum probable.

Based on the current forecast, the February 24-Month study projects Lake
Powell elevation will peak near approximately 3,611 ft next summer and end
the water year near 3,604 feet with approximately 12.16 maf in storage (50%
capacity). Note that projections of elevation and storage have significant
uncertainty at this point in the season, primarily due to uncertainty
regarding the season’s total snowpack and the resulting inflow to Lake
Powell. Under the minimum probable inflow scenario, updated in January, the
projected summer peak is 3,592 ft and end of water year storage is 9.7 maf
(40% capacity). Under the maximum probable inflow scenario, updated in
January, the projected summer peak is 3,631 ft and end of water year storage
is 15.0 maf (62% capacity). There is a 10 percent chance that inflows will
be higher, resulting in higher elevation and storage, and 10 percent chance
that inflows will be lower, resulting in lower elevation and storage. The
minimum and maximum probable model runs will be updated again in April. The
annual release volume from Lake Powell during water year 2014 is projected
to be 7.48 maf under all inflow scenarios.

Consistent with Section 6.C.1 of the Interim Guidelines, the Lake Powell
operational tier for water year 2014 is the Mid-Elevation Release Tier with
an annual release volume of 7.48 maf. This was determined in the August 2013
24-Month Study and documented in the 2014 Annual Operating Plan signed by
Secretary Jewell in December 2013.

Upper Colorado River Basin Hydrology

The Upper Colorado River Basin regularly experiences significant year to
year hydrologic variability. During the 14-year period 2000 to 2013,
however, the unregulated inflow to Lake Powell, which is a good measure of
hydrologic conditions in the Colorado River Basin, was above average in only
3 out of the past 14 years. The period 2000-2014 is the lowest 14-year
period since the closure of Glen Canyon Dam in 1963, with an average
unregulated inflow of 8.25 maf, or 76% of the 30-year average (1981-2010).
(For comparison, the 1981-2010 total water year average is 10.83maf.) The
unregulated inflow during the 2000-2013 period has ranged from a low of 2.64
maf (24% of average) in water year 2002 to a high of 15.97 maf (147% of
average) in water year 2011. Under the current forecast, total water year
2014 inflows to Lake Powell are expected to range between a minimum probable
of 7.92 maf (73% of average) and a maximum probable of 13.47 maf (124% of
average) with a most probable projection of 10.42 maf (96% of average).

At the beginning of water year 2014, total system storage in the Colorado
River Basin was 29.9 maf (50% of 59.6 maf total system capacity). This is
about 4 maf less than the total storage at the beginning of water year 2013
which began at 34.0 maf (57% of capacity). Since the beginning of water year
2000, total Colorado Basin storage has experienced year to year increases
and decreases in response to wet and dry hydrology, ranging from a high of
94% of capacity at the beginning of 2000 to a low of 50% of capacity at the
beginning of water year 2014. One wet year can significantly increase total
system reservoir storage, just as persistent dry years can draw down the
system storage. Based on current inflow forecasts, the current projected end
of water year 2014 total Colorado Basin reservoir storage is approximately
30.1 maf (51% of capacity). The actual end of water year storage may vary
significantly from this projection, primarily due to uncertainty regarding
this season’s snowpack and resulting runoff. Based on January minimum and
maximum probable inflow forecasts and modeling the range is approximately
26.9 maf (45%) to 33.6 maf (56%), respectively

This update courtesy of Katrina Grantz, Bureau of Reclamation

 

December 11/13

Current Status The unregulated inflow volume to Lake Powell in November was 460 thousand acre-feet (kaf) (97% of average). The release volume from Glen Canyon Dam in November was 680 kaf. On November 11-16 a high flow experimental release was conducted from Glen Canyon Dam in accordance with the High Flow Protocol. Reclamation released the maximum available capacity (35,000 cfs) during the 5-day experiment. The end of November elevation and storage of Lake Powell were 3587.9 feet (112.1 feet from full pool) and 10.63 million acre-feet (maf) (44% of full capacity), respectively. The annual release volume from Lake Powell remains 7.48 maf and will not change as a result of the HFE. The reservoir elevation is now declining and will continue to decline through the fall and winter until spring runoff in 2014.
Current Operations The operating tier for water year 2014 is the Mid-Elevation Release Tier with an annual release volume of 7.48 maf, as established in August 2013 and pursuant to the Interim Guidelines, Section 6.C.1. Reclamation will schedule operations at Glen Canyon Dam to achieve as practicably as possible a 7.48 maf annual release volume by September 30, 2014.
In December, the release volume will likely be about 600 kaf, with fluctuations from about 6,000 cfs in the daytime to about 12,000 cfs in the nighttime and consistent with the Glen Canyon Operating Criteria (Federal Register, Volume 62, No. 41, March 3, 1997). In January, the release volume will likely be about 800 kaf with daily fluctuations for hydropower between 8,500 cfs and 16,500 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 1,200 cfs above or below the hourly scheduled release rate. Under system normal conditions, fluctuations for regulation are typically short lived and generally balance out over the hour with minimal or no 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 41 MW of reserves (approximately 1,200 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 41 MW.
December 2013
2
Inflow Forecasts and Model Projections The hydrologic forecast for water year 2014 for Lake Powell, issued by the Colorado Basin River Forecast Center, projects that the most probable (median) unregulated inflow volume will be 10.21 maf (94% of average based on the period 1981-2010). The water year 2014 forecast increased by 560 kaf since last month. At this early point in the season, there is still significant uncertainty regarding next year’s water supply. The forecast ranges from a minimum probable of 6.5 maf (60% of average) to a maximum probable of 16.5 maf (162% of average). There is a 10 percent chance that inflows could be higher than the maximum probable and a 10 percent chance they could be lower than the minimum probable.
Based on the current forecast, the December 24-Month study projects Lake Powell elevation will peak near approximately 3,608 ft next summer and end the water year near 3,603 feet with approximately 12.08 maf in storage (50% capacity). Note that projections of elevation and storage have significant uncertainty at this point in the season, primarily due to uncertainty regarding the upcoming winter’s total snowfall and the resulting inflow to Lake Powell. Under the minimum probable inflow scenario, last run in October, the projected summer peak is 3,586 ft and end of water year storage is 9.3 maf (38% capacity). Under the maximum probable inflow scenario, last run in October, the projected summer peak is 3,661 ft and end of water year storage is 18.4 maf (76% capacity). There is a 10 percent chance that inflows will be higher, resulting in higher elevation and storage, and 10 percent chance that inflows will be lower, resulting in lower elevation and storage. The minimum and maximum probable model runs will be updated in January. The annual release volume from Lake Powell during water year 2014 is projected to be 7.48 maf under all inflow scenarios.
Consistent with Section 6.C.1 of the Interim Guidelines, the Lake Powell operational tier for water year 2014 is the Mid-Elevation Release Tier with an annual release volume of 7.48 maf. This was determined in the August 2013 24-Month study tier determination run which projected that, with an 8.23 maf annual release pattern in water year 2014, the January 1, 2014, Lake Powell elevation would be below 3,575.0 feet and the Lake Mead elevation would be above 1,025.0 feet. This determination will be documented in the 2014 AOP, which is currently in the final stages of development.
Upper Colorado River Basin Hydrology The Upper Colorado River Basin regularly experiences significant year to year hydrologic variability. During the 14-year period 2000 to 2013, however, the unregulated inflow to Lake Powell, which is a good measure of hydrologic conditions in the Colorado River Basin, was above average in only 3 out of the past 14 years. The period 2000-2014 is the lowest 14-year period since the closure of Glen Canyon Dam in 1963, with an average unregulated inflow of 8.25 maf, or 76% of the 30-year average (1981-2010). (For comparison, the 1981-2010 average is 10.83maf.) The unregulated inflow during the 2000-2013 period has ranged from a low of 2.64 maf (24% of average) in water year 2002 to a high of 15.97 maf (147% of average) in water year 2011. Under the current forecast, water year 2014 inflows to Lake Powell are expected to
December 2013
3
range between a minimum probable of 6.5 maf (60% of average) and a maximum probable of 16.5 maf (162% of average) with a most probable projection of 10.21 maf (94% of average).
At the beginning of water year 2014, total system storage in the Colorado River Basin was 29.9 maf (50% of 59.6 maf total system capacity). This is about 4 maf less than the total storage at the beginning of water year 2013 which began at 34.0 maf (57% of capacity). Since the beginning of water year 2000, total Colorado Basin storage has experienced year to year increases and decreases in response to wet and dry hydrology, ranging from a high of 94% of capacity at the beginning of 2000 to a low of 50% of capacity at the beginning of water year 2014. One wet year can significantly increase total system reservoir storage, just as persistent dry years can draw down the system storage. Based on current inflow forecasts, the current projected end of water year 2014 total Colorado Basin reservoir storage is approximately 31.1 maf (51% of capacity). The actual end of water year storage may vary significantly from this projection, primarily due to uncertainty regarding next season’s snowpack and resulting runoff.
Updated December 10, 2013 Katrina Grantz

 

November 2013
1
Glen Canyon Dam / Lake Powell
Current Status
The unregulated inflow volume to Lake Powell in October was 549 thousand acre-feet
(kaf) (107% of average). The release volume from Glen Canyon Dam in October was
481 kaf. The end of October elevation and storage of Lake Powell were 3590.9 feet
(109.1 feet from full pool) and 10.90 million acre-feet (maf) (45% of full capacity),
respectively. The reservoir elevation is now declining and will continue to decline
through the fall and winter until spring runoff in 2014.
Current Operations
The operating tier for water year 2014 is the Mid-Elevation Release Tier with an annual
release volume of 7.48 maf, as established in August 2013 and pursuant to the Interim
Guidelines, Section 6.C.1. Reclamation will schedule operations at Glen Canyon Dam to
achieve as practicably as possible a 7.48 maf annual release volume by September 30,
2014.
From November 11-16, 2013, the Department of Interior is conducting a High Flow
Experiment (HFE). Under the HFE Protocol, high flow releases are linked to sediment
input and other resource conditions below Glen Canyon Dam. During the HFE, total
releases from Glen Canyon Dam at full powerplant capacity and bypass may reach
approximately 34,100 cfs. Releases will be maintained at peak release for 4 days (96
hours). The total experiment, including ramping, is expected to last just over five days.
November releases from Glen Canyon Dam prior to and after the HFE are expected to
fluctuate between 5,000cfs and 8,000cfs. The elevation of Lake Powell is expected to
decrease approximately 2 ½ feet during the 5 day experiment. The total release volume
in November, including the HFE, will be approximately 670 kaf. The annual release
volume from Lake Powell remains 7.48 maf and will not change as a result of the HFE.
In December, the release volume will likely be about 600 kaf, with fluctuations from
about 6,000 cfs in the daytime to about 12,000 cfs in the nighttime and consistent with
the Glen Canyon Operating Criteria (Federal Register, Volume 62, No. 41, March 3,
1997). In January, the release volume will likely be about 800 kaf with daily
fluctuations for hydropower.
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 1,200 cfs above or below the
hourly scheduled release rate. Under system normal conditions, fluctuations for
regulation are typically short lived and generally balance out over the hour with minimal
or no 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
November 2013
2
reliability in the event of an unscheduled outage. Glen Canyon Dam typically maintains
41 MW of reserves (approximately 1,200 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 41 MW.
Inflow Forecasts and Model Projections
The hydrologic forecast for water year 2014 for Lake Powell, issued by the Colorado
Basin River Forecast Center, projects that the most probable (median) unregulated inflow
volume will be 9.75 maf (90% of average based on the period 1981-2010). The water
year 2014 forecast increased slightly (100 kaf) since last month. At this early point in the
season, there is significant uncertainty regarding next year’s water supply. The forecast
ranges from a minimum probable of 6.5 maf (60% of average) to a maximum probable of
16.5 maf (162% of average). There is a 10 percent chance that inflows could be higher
than the maximum probable and a 10 percent chance they could be lower than the
minimum probable.
Based on the current forecast, the November 24-Month study projects Lake Powell
elevation will peak near approximately 3,605 ft next summer and end the water year near
3,599 feet with approximately 11.68 maf in storage (48% capacity). Note that projections
of elevation and storage have significant uncertainty at this point in the season, primarily
due to uncertainty regarding next season’s snowpack and resulting inflow to Lake
Powell. Under the minimum probable inflow scenario, last run in October, the projected
summer peak is 3,586 ft and end of water year storage is 9.3 maf (38% capacity). Under
the maximum probable inflow scenario, last run in October, the projected summer peak is
3,661 ft and end of water year storage is 18.4 maf (76% capacity). There is a 10 percent
chance that inflows will be higher, resulting in higher elevation and storage, and 10
percent chance that inflows will be lower, resulting in lower elevation and storage. The
annual release volume from Lake Powell during water year 2014 is projected to be 7.48
maf under all inflow scenarios.
Consistent with Section 6.C.1 of the Interim Guidelines, the Lake Powell operational tier
for water year 2014 is the Mid-Elevation Release Tier with an annual release volume of
7.48 maf. This was determined in the August 2013 24-Month study tier determination
run which projected that, with an 8.23 maf annual release pattern in water year 2014, the
January 1, 2014, Lake Powell elevation would be below 3,575.0 feet and the Lake Mead
elevation would be above 1,025.0 feet. This determination will be documented in the
2014 AOP, which is currently in the final stages of development.
Upper Colorado River Basin Hydrology
The Upper Colorado River Basin regularly experiences significant year to year
hydrologic variability. During the 14-year period 2000 to 2013, however, the
unregulated inflow to Lake Powell, which is a good measure of hydrologic conditions in
the Colorado River Basin, was above average in only 3 out of the past 14 years. The
November 2013
3
period 2000-2014 is the lowest 14-year period since the closure of Glen Canyon Dam in 1963, with an average unregulated inflow of 8.25 maf, or 76% of the 30-year average (1981-2010). (For comparison, the 1981-2010 average is 10.83maf.) The unregulated inflow during the 2000-2013 period has ranged from a low of 2.64 maf (24% of average) in water year 2002 to a high of 15.97 maf (147% of average) in water year 2011. Under the current forecast, water year 2014 inflows to Lake Powell are expected to range between a minimum probable of 6.5 maf (60% of average) and a maximum probable of 16.5 maf (162% of average) with a most probable projection of 9.75 maf (90% of average).
At the beginning of water year 2014, total system storage in the Colorado River Basin was 29.9 maf (50% of 59.6 maf total system capacity). This is about 4 maf less than the total storage at the beginning of water year 2013 which began at 34.0 maf (57% of capacity). Since the beginning of water year 2000, total Colorado Basin storage has experienced year to year increases and decreases in response to wet and dry hydrology, ranging from a high of 94% of capacity at the beginning of 2000 to a low of 50% of capacity at the beginning of water year 2014. One wet year can significantly increase total system reservoir storage, just as persistent dry years can draw down the system storage. Based on current inflow forecasts, the current projected end of water year 2014 total Colorado Basin reservoir storage is approximately 29.6 maf (50% of capacity). The actual end of water year storage may vary significantly from this projection, primarily due to uncertainty regarding next season’s snowpack and resulting runoff.
Updated November 14, 2013
Katrina Grantz

August 19, 2013

Current Status

The unregulated inflow volume to Lake Powell in July was 143 thousand
acre-feet (kaf) (13% of average). The release volume from Glen Canyon Dam
in July was 848 kaf. The end of July elevation and storage of Lake Powell
were 3594.2 feet (106 feet from full pool) and 11.20 million acre-feet
(maf)
(46% of full capacity), respectively. The reservoir elevation peaked in
mid-June at 3601.2 ft and is now declining. The elevation will continue
to
decline through the fall and winter until spring runoff in 2014.

Current Operations

The operating tier for 2013 is the Upper Elevation Balancing Tier, as
established in August 2012 and pursuant to the Interim Guidelines. Since
the April 2013 projected end of water year elevation at Lake Powell was
below the 2013 Equalization Elevation of 3,646.0 feet and the projected
end
of water year elevation at Lake Mead was above elevation 1,075.0 feet,
Section 6.B.1 and 6.B.4 of the Interim Guidelines provide for an annual
release volume of 8.23 maf from Lake Powell during water year 2013.
Reclamation will schedule operations at Glen Canyon Dam to achieve as
practicably as possible an 8.23 maf annual release volume by September 30,
2013.

Releases from Glen Canyon Dam in August are currently averaging
approximately 13,000 cfs with daily fluctuations between approximately 9,000
cfs at nighttime and approximately 17,000 cfs during the daytime and
consistent with the Glen Canyon Operating Criteria (Federal Register,
Volume
62, No. 41, March 3, 1997). The scheduled release volume for August 2013 is
800 kaf.

In September, the release volume will likely be about 600 kaf, with daily
fluctuations for hydropower between approximately 7,000 cfs in the
nighttime
and approximately 13,000 cfs in the daytime. In October, the release volume
will likely be about 480 kaf with daily fluctuations between approximately
5,000 cfs and 10,000 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 1,200 cfs above or below the hourly scheduled release rate.
Under
system normal conditions, fluctuations for regulation are typically short
lived and generally balance out over the hour with minimal or no
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 1,200 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.

Inflow Forecasts and Model Projections

The hydrologic forecast for Lake Powell, issued by the Colorado Basin River
Forecast Center, projects that the most probable (median) unregulated inflow
volume for water year 2013 will be 4.33 maf (40% of average based on the
period 1981-2010). The water year 2013 forecast decreased from last
month,
due to significantly below average inflows in July. Based on the current
forecast, the August 24-Month study projects Lake Powell elevation will
decline approximately 8 feet through August and September and end the
water
year at 3585.7 feet with 10.4 maf in storage (43% capacity). The annual
release volume from Lake Powell during water year 2013 is scheduled to be
8.23 maf. Reclamation will schedule operations at Glen Canyon Dam to
achieve
as practicably as possible an 8.23 maf annual release volume by September
30, 2013.

The hydrologic forecast for Lake Powell for water year 2014 projects that
the most probable (median) unregulated inflow volume will be 8.32 maf (77%
of average based on the period 1981-2010). At this early point in the
season, there is significant uncertainty regarding next year’s water
supply.
The forecast ranges from a minimum probable (90% exccedence) of 5.0 maf (46%
of average) to a maximum probable (10% exceedence) of 15.5 maf (143% of
average). There is a 10% chance that inflows could be higher than the
maximum probable and a 10% chance they could be lower than the minimum
probable.

Consistent with Section 6.C.1 of the Interim Guidelines, if the August
24-Month study projects the January 1, 2014, Lake Powell elevation to be
less than 3,575.0 feet and at or above 3,525.0 feet and the Lake Mead
elevation to be at or above 1,025.0 feet, the operational tier for Lake
Powell in water year 2014 will be the Mid-Elevation Release Tier and the
water year release volume from Lake Powell would be 7.48 maf. The August
2013 24-Month study projects that, with an 8.23 maf annual release pattern
in water year 2014, the January 1, 2014, Lake Powell elevation would be
3,573.69 feet and the Lake Mead elevation would be 1,107.39 feet.
Therefore,
consistent with Section 6.C.1 of the Interim Guidelines, the Lake Powell
operational tier for water year 2014 is the Mid-Elevation Release Tier
with
an annual release volume of 7.48 maf. This determination will be
documented
in the 2014 AOP, which is currently in the final stages of development.

Upper Colorado River Basin Hydrology

Since 2005 the Upper Colorado River Basin has experienced significant year
to year hydrologic variability. During the period 2005 through 2012, the
unregulated inflow to Lake Powell, which is a good measure of hydrologic
conditions in the Colorado River Basin, averaged a water year volume of
10.22 maf (94% of average (period 1981-2010)). The unregulated inflow has
ranged from a low of 4.91 maf (45% of average) in water year 2012 to a
high
of 15.97 maf (147% of average) in water year 2011. This has been an
improvement over the persistent drought conditions of 2000 to 2004, which
averaged a water year unregulated inflow of 5.73 maf. However, based on
observed inflows and current forecasts, water year 2013 unregulated inflow
is expected to be 4.33 maf (40% of average), which would be a second
significantly below-average year in a row. If this occurs, the period
2000-2013 would be the driest 14-year period on record with an average
annual unregulated inflow of 8.20 maf per year. (For comparison, the
standard 1981-2010 period average is 10.83 maf).

At the beginning of water year 2013, total system storage in the Colorado
River Basin was 33.9 maf (57 % of capacity), which was an increase of
about
4 maf since water year 2005 which began at 29.8 maf (50% of capacity). Since
2005, however, total Colorado Basin storage has experienced year to year
increases and decreases in response to wet and dry hydrology. In
addition,
conditions in both 2012 and 2013 have been significantly drier than average
and based on observed inflows and current forecasts, the current projected
end of water year 2013 total Colorado Basin reservoir storage is
approximately 29.0 maf (49% of capacity).

This update courtesy of Katrina Grantz, Bureau of Reclamation

 

 

 

January 25, 2013

This notification confirms that the release volume from Glen Canyon Dam for February 2013 will be 600,000 acre-feet. Hourly and daily average releases from Glen Canyon Dam for February 2013 will be scheduled through Western Area Power Administration to be consistent with the Glen Canyon Dam Operating Criteria (Federal Register, Volume 62, No. 41, March 3, 1997) and to also achieve, as nearly as is practicable, this monthly volume.

Hourly releases during February 2013 are anticipated to peak in the morning at approximately 12,000 cfs and again in the evening at 14,000 cfs with nighttime and mid-day low releases of approximately 8,000 cfs.

We anticipate the release volume for March 2013 will be 600,000 acre-feet with double-peaking fluctuations between approximately 7,000 cfs and 13,000 cfs. The anticipated release volume for April 2013 is 550,000 acre-feet. This will be confirmed in a subsequent notification toward the end of February.

This notification supersedes all previously issued notifications and is current until a new notification is issued. All times identified in this notification are local time (Mountain Standard Time) and not hour ending.

Glen Canyon Dam / Lake Powell –12/12/12
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

August 13, 2012

Present Dam Operations

The monthly unregulated inflow volume to Lake Powell for July was 154
thousand acre-feet (kaf) or 14% of average. The release volume from Glen
Canyon Dam in July was 886 kaf. The end of July elevation and storage of
Lake Powell was 3628.45 feet (71.55 feet from full pool) and 14.68 million
acre feet (maf) or 60.4% of full capacity. The reservoir elevation is now
declining.

The April through July unregulated inflow volume for 2012 was 2.06 maf or
29% of average, placing the 2012 April to July season as the third driest
on record since the closure of Glen Canyon Dam in 1963. Only 1977 and 2002
had lower April-July unregulated inflow volumes to Lake Powell than what
occurred in 2012. In terms of reservoir elevation and storage, Lake Powell
reached its peak for water year 2012 on June 3rd at 3636.90 ft, or 63.1
feet from full pool and 15.640 maf equaling 64.30% of capacity,
respectively. The peak elevation in 2012 is 24 feet below the 2011 peak
elevation of 3660.90ft.

Current Dam Operations

Releases from Glen Canyon Dam are now averaging about 13,500 cubic feet
per second (cfs) with fluctuations for power generation throughout the day
that peak near 17,000 cfs in the afternoons and with early morning low
level releases are about 9,000 cfs and this operation is consistent with
the Glen Canyon Operating Criteria (Federal Register, Volume 62, No. 41,
March 3, 1997). The release volume for August is scheduled to be 800 kaf
and meets the targeted release volume of the 2012 Hydrograph that was
approved by the Secretary of the Interior. In September and October, as
part of the 2008 FONSI, releases from Glen Canyon Dam will be steady for a
steady flow experiment. The targeted release rate for September and
October of 2012 is 8,000 cfs, with volumes of 476 kaf and 491kaf,
respectively.

In addition to daily scheduled fluctuations for power generation, the
instantaneous releases from Glen Canyon Dam may also fluctuate to provide
40 megawatts (MW) of system regulation. These instantaneous release
adjustments stabilize the electrical generation and transmission system
and translate to a range of about 1100 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). There are many generators that supply electricity
to the transmission system within the balancing area. At times, a
participating generator may experience operating conditions such that it
cannot make its scheduled delivery of electricity to the system (i.e.
unscheduled outage). To provide system reliability, all participating
electricity generators within the balancing area maintain a specified
level of generation capacity (i.e. reserves) that can be called upon when
an unscheduled outage occurs. Glen Canyon Dam typically maintains 113 MW
of reserves for this purpose.

Reserve agreements allow the controllers of the balancing area to call
upon Glen Canyon Dam to produce up to an additional 113 MW of electricity
beyond what is originally scheduled for a given hour. Reserve calls can be
maintained for a maximum of 2 hours after which time the generation rate
should be returned to the original schedule. The 113 MW reserve
requirement for Glen Canyon Dam translates to approximately 2,800 cfs of
flow in the river. When the balancing area controllers call for reserve
generation from Glen Canyon Dam, releases from the dam can exceed
scheduled levels and have a noticeable impact on the river downstream from
Glen Canyon Dam. But these calls for reserves are fairly infrequent and
typically are for much less than the required level of 113 MW.

In August 2011, pursuant to the Interim Guidelines, the Operating Tier for
Glen Canyon Dam was established to be the Equalization Tier. Under the
Equalization Tier when conditions dry out as they have this year, the
minimum annual release from Lake Powell can generally be as low as 8.23
maf. However, water year 2011 was a very wet Equalization year and not all
of the Equalization release volume for 2011 could be achieved by September
30, 2011. As a result, 1.233 maf of the 2011 Equalization release volume
was actually released after the end of water year 2011. This increased the
minimum release volume for water year 2012 under Equalization to 9.463
maf. Under the dry hydrologic conditions currently projected for Lake
Powell, the water year 2012 release volume is projected to be at this
minimum Equalization level of 9.463 maf. 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 2012 to achieve Equalization objectives as practicably as possible
by September 30, 2012.

Current Inflow Forecasts and Model Projections

Over the next three months (July, August and September) the forecasted
unregulated inflow volume to Lake Powell is projected to be 200 kaf (40%
of average), 250 kaf (61% of average) and 350 kaf (68% of average),
respectively. These percent of averages are all based on the historic
period from 1981 through 2010. The most probable (i.e. 50% likely to be
exceeded) unregulated inflow volume for WY2012 is projected to be 5.15 maf
(48% of average). Comparing this projected water year unregulated inflow
volume to the driest year on record (2002) in which the unregulated inflow
volume was only 2.64 maf (24% of average), water year 2012 will likely be
very dry, yet not nearly as dry as conditions were in 2002. The currently
projected water year unregulated inflow volume of 5.15 maf would rank as
the 3rd driest year on record since the closure of Glen Canyon Dam (1963).

The 2012 annual release volume from Glen Canyon Dam will likely be 9.463
maf and the elevation of Lake Powell at the end of WY2012 is projected to
be 3623.1 feet above sea level which is 76.9 feet from the full pool
elevation of 3700 feet. This elevation corresponds to a live storage
volume of 14.09 maf (58 % of full capacity). These projections are based
on conditions in the August 24-Month Study.

The hydrologic outlook forecast for water year 2013 projects that the most
probable (median) unregulated inflow volume will be 8.85maf (82% of
average based on the period 1981-2010). Based on this hydrologic outlook,
the August 2012 24-Month Study projects the annual release from lake
Powell during water year 2013 will be 8.23 maf and the end of water year
2013 reservoir elevation and storage for Lake Powell to be 3618.19 feet
(81.8 feet from full pool) and 13.573 maf (55.8% capacity), respectively.

The August 2012 24-Month Study has been published and is available here:
http://www.usbr.gov/uc/water/crsp/studies/24Month_08.pdf

The September 2012 24-Month Study will be published by September 15, 2012
and a link to this study will be provided at this website. Updated
elevation projections for Lake Powell through water year 2013 based on the
most recently published 24-Month Study are maintained at:
http://www.usbr.gov/uc/water/crsp/studies/lppwse2.html

Upper Colorado River Basin Hydrology

Since water year 2005, hydrologic conditions in the Upper Colorado River
Basin have been near average with significant variability from year to
year. The unregulated inflow to Lake Powell, which is a good measure of
the hydrologic condition in the Colorado River Basin, has averaged a water
year volume of 10.98 maf (101% of average (period 1981-2010)) during the
period from 2005 through 2011. The hydrologic variability during this
period has been from a low water year unregulated inflow volume of 8.62
maf (80% of average) in water year 2006 to a high water year unregulated
inflow volume of 15.97 maf (147% of average) which occurred in water year
2011. However, based on observed inflows and current forecasts, water year
2012 unregulated inflow is expected to be 5.15 maf (47.6% of average),
which would be the lowest water year unregulated inflow volume since 2002.

Overall reservoir storage in the Colorado River Basin has increased by
over 8 maf since the beginning of water year 2005 and this is a
significant improvement over the drought conditions during water years
2000 through 2004. On October 1, 2004, the beginning of water year 2005,
the total reservoir storage in the Colorado River Basin was 29.84 maf
(50.2% of capacity). On October 1, 2011, the beginning of water year 2012,
the total reservoir storage in the Colorado River Basin was 38.66 maf
(64.8% of capacity). As of August 9, 2012 the total reservoir storage in
the Colorado River Basin was 35.18 maf (59.0% of capacity).

 

July 9, 2012

Glen Canyon Dam / Lake Powell

For the Water Supply period April through July, 2012 will most likely be the
third driest year on record since the closure of Glen Canyon Dam in 1963.
Only 1977 and 2002 will have had lower April-July unregulated inflow
volumes to Lake Powell than what is most likely to occur in 2012.

The monthly unregulated inflow volume to Lake Powell for June was 353
thousand acre-feet (kaf) (13% of average). This was very nearly equal to
the forecasted unregulated inflow volume at the beginning of June which was 350
kaf. The release volume from Glen Canyon Dam in June was 709 kaf which was
1,000 acre-feet above what was scheduled for release during the month. The
end of June elevation and storage of Lake Powell was 3633.90 feet (66.10
feet from full pool) and 15.29 million acre-feet (maf) (62.88% of full
capacity).

The Water Supply Forecast for Lake Powell (April through July Unregulated
Inflow Volume) for July remained unchanged from June at 2.01 maf (28% of
average).

Current Dam Operations

In August 2011, pursuant to the Interim Guidelines, the Operating Tier for
Glen Canyon Dam was established to be the Equalization Tier. Under the
Equalization Tier when conditions dry out as they have this year, the
minimum annual release from Lake Powell can generally be as low as 8.23
maf.
However, water year 2011 was a very wet Equalization year and not all of the
Equalization release volume for 2011 could be achieved by September 30,
2011. As a result, 1.233 maf of the 2011 Equalization release volume was
actually released after the end of water year 2011. This increased the
minimum release volume for water year 2012 under Equalization to 9.463
maf.
Under the dry hydrologic conditions currently projected for Lake Powell, the
water year 2012 release volume is projected to be at this minimum
Equalization level of 9.463 maf. 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 2012 to
achieve Equalization objectives as practicably as possible by September
30, 2012.

Releases from Glen Canyon Dam are now averaging about 14,500 cubic feet per
second (cfs) with fluctuations for power generation throughout the day that
peak near 18,000 cfs in the afternoons and with early morning low level
releases are about 10,000 cfs and this operation is consistent with the
Glen Canyon Operating Criteria (Federal Register, Volume 62, No. 41, March 3,
1997). The release volume for July is scheduled to be 889 kaf and this
volume is elevated slightly in order to target a release volume in August
of 800 kaf. In August, fluctuations are projected to peak near 17,000 cfs
during the afternoons with early morning low releases near 9,000 cfs. In
September and October, as part of the 2008 FONSI, releases from Glen
Canyon Dam will be steady for a steady flow experiment. The targeted release rate
for September and October of 2012 is 8,000 cfs.

In addition to daily scheduled fluctuations for power generation, the
instantaneous releases from Glen Canyon Dam may also fluctuate to provide
40 megawatts (MW) of system regulation. These instantaneous release
adjustments stabilize the electrical generation and transmission system and translate to
a range of about 1100 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). There are many generators that supply electricity to the
transmission system within the balancing area. At times, a participating
generator may experience operating conditions such that it cannot make its
scheduled delivery of electricity to the system (i.e. unscheduled outage).
To provide system reliability, all participating electricity generators
within the balancing area maintain a specified level of generation
capacity (i.e. reserves) that can be called upon when an unscheduled outage occurs.
Glen Canyon Dam typically maintains 113 MW of reserves for this purpose.

Reserve agreements allow the controllers of the balancing area to call upon
Glen Canyon Dam to produce up to an additional 113 MW of electricity beyond
what is originally scheduled for a given hour. Reserve calls can be
maintained for a maximum of 2 hours after which time the generation rate
should be returned to the original schedule. The 113 MW reserve
requirement

for Glen Canyon Dam translates to approximately 2,800 cfs of flow in the
river. When the balancing area controllers call for reserve generation
from Glen Canyon Dam, releases from the dam can exceed scheduled levels and have
a noticeable impact on the river downstream from Glen Canyon Dam. But these
calls for reserves are fairly infrequent and typically are for much less
than the required level of 113 MW.

Current Inflow Forecasts and Model Projections

Over the next three months (July, August and September) the forecasted
unregulated inflow volume to Lake Powell is projected to be 100 kaf (9% of
average), 150 kaf (30% of average) and 200 kaf (49% of average),
respectively. These percent of averages are all based on the historic period
from 1981 through 2010. The most probable (i.e. 50% likely to be
exceeded) unregulated inflow volume for WY2012 is projected to be 5.0 maf (46% of
average). Comparing this projected water year unregulated inflow volume to
the driest year on record (2002) in which the unregulated inflow volume
was only 2.64 maf (24% of average), water year 2012 will likely be very dry, yet
not nearly as dry as conditions were in 2002. The currently projected water
year unregulated inflow volume of 5.0 maf would rank as the 3rd driest year
on record since the closure of Glen Canyon Dam (1963).

The annual release volume from Glen Canyon Dam will likely be 9.463 maf and
the elevation of Lake Powell at the end of WY2012 is projected to be 3622.6
feet above sea level which is 77.4 feet from the full pool elevation of 3700
feet. This elevation corresponds to a live storage volume of 14.04 maf (58
% of full capacity). These projections are based on conditions in the July
24-Months Study.

The June 2012 24-Month Study has been published and is available here. The
July 2012 24-Month Study will be published by July 13, 2012 and a link to
this study will be provided at this website. Updated elevation projections
for Lake Powell through water year 2012 based on the most recently
published
24-Month Study are maintained at: Lake Powell Projected Elevations.

Upper Colorado River Basin Hydrology

Since water year 2005, hydrologic conditions in the Upper Colorado River
Basin have been near average with significant variability from year to
year.
The unregulated inflow to Lake Powell, which is a good measure of the
hydrologic condition in the Colorado River Basin, has averaged a water
year
volume of 10.98 maf (101% of average (period 1981-2010)) during the period
from 2005 through 2011. The hydrologic variability during this period has
been from a low water year unregulated inflow volume of 8.62 maf (80% of
average) in water year 2006 to a high water year unregulated inflow volume
of 15.97 maf (147% of average) which occurred in water year 2011.

Overall reservoir storage in the Colorado River Basin has increased by over
8 maf since the beginning of water year 2005 and this is a significant
improvement over the drought conditions during water years 2000 through
2004. On October 1, 2004, the beginning of water year 2005, the total
reservoir storage in the Colorado River Basin was 29.84 maf (50.2% of
capacity). On October 1, 2011, the beginning of water year 2012, the total
reservoir storage in the Colorado River Basin was 38.66 maf (64.8% of
capacity). As of July 8, 2012 the total reservoir storage in the Colorado
River Basin was 35.80 maf (60.0% of capacity).

Updated 5/26/12

The purpose of this notification is to confirm that the release volume from Glen Canyon Dam for June 2012 will be 708,000 acre-feet. Hourly and daily average releases from Glen Canyon Dam for June 2012 will be scheduled through Western Area Power Administration to be consistent with the Glen Canyon Dam Operating Criteria (Federal Register, Volume 62, No. 41, March 3, 1997) and to also achieve, as nearly as is practicable, this monthly volume.

Hourly releases during June 2012 are anticipated to peak in the afternoon to approximately 15,000 cfs with early morning hourly low releases of approximately 9,000 cfs.

We anticipate the release volume for July 2012 will be 890,000 acre-feet. This will be confirmed in a subsequent notification toward the end of May.

This notification supersedes all previously issued notifications and is current until a new notification is issued. All times identified in this notification are local time (Mountain Standard Time) and not hour ending.

 

 

Updated: May 10, 2012

Glen Canyon Dam / Lake Powell –The monthly unregulated inflow volume to Lake
Powell for April was 764 thousand acre-feet (kaf) (72% of average). This was 36 kaf
below what was forecasted in early April. The release volume from Glen Canyon Dam in
April was 606 kaf which was 6,000 acre-feet above what was scheduled for release
during the month. As a result of the difference between the projections made in early
April and actual conditions and operations that occurred in April, the elevation of Lake
Powell at the end of April was 0.17 feet (about 2 inches) higher than projected. On April
30, 2012 the elevation of Lake Powell was 3635.76 feet above sea level (64.24 feet below
full pool).
Snowpack conditions above Lake Powell have been well below average all year and are
now nearly melted out. The runoff from the melting snow has been less than impressive
and the inflow to Lake Powell so far has peaked at just over 15,000 cfs. It is possible that
this peak could be exceeded if temperature conditions warm quickly in the coming
weeks. The Water Supply Forecast for Lake Powell (April through July Unregulated
Inflow Volume) has been updated for May and the forecasted unregulated inflow volume
for the period from April through July for Lake Powell is now 2.36 maf (33% of
average). This is the third driest May forecast for Lake Powell since these forecasts began
to be issued. Only 1977 and 2002 had lower May forecasts and these years ultimately
were the 2 driest water years in the historic record for Lake Powell (1963-2011).
Current Dam Operations
In August 2011, pursuant to the Interim Guidelines, the Operating Tier for Glen Canyon
Dam was established to be the Equalization Tier. Under the Equalization Tier when
conditions dry out as they have this year, the minimum annual release from Lake Powell
can generally be as low as 8.23 maf. However, water year 2011 was a very wet
Equalization year and not all of the Equalization release volume for 2011 could be
achieved by September 30, 2011. As a result, 1.233 maf of the 2011 Equalization release
volume was actually released after the end of water year 2011. This increased the
minimum release volume for water year 2012 under Equalization to 9.463 maf. Under the
dry hydrologic conditions currently projected for Lake Powell, the water year 2012
release volume is projected to be at this minimum Equalization level of 9.463 maf. 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 2012 to achieve Equalization objectives as practicably as possible by
September 30, 2012.
Releases from Glen Canyon Dam are now averaging about 10,050 cfs with fluctuations
for power generation throughout the day that peak near 12,500 cfs in the afternoons and
with early morning low level releases are about 6,500 cfs and this operation is consistent
with the Glen Canyon Operating Criteria (Federal Register, Volume 62, No. 41, March 3,
1997). The release volume for May is scheduled to be 600 kaf. In June, the monthly
release volume will likely be about 707 kaf kaf. Release fluctuations in June are projected
to be in the range from about 9,000 cfs during the early morning hours to an afternoon
peak of about 15,000 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 1100 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). There are many generators that
supply electricity to the transmission system within the balancing area. At times, a
participating generator may experience operating conditions such that it cannot make its
scheduled delivery of electricity to the system (i.e. unscheduled outage). To provide
system reliability, all participating electricity generators within the balancing area
maintain a specified level of generation capacity (i.e. reserves) that can be called upon
when an unscheduled outage occurs. Glen Canyon Dam typically maintains 113 MW of
reserves for this purpose.
Reserve agreements allow the controllers of the balancing area to call upon Glen Canyon
Dam to produce up to an additional 113 MW of electricity beyond what is originally
scheduled for a given hour. Reserve calls can be maintained for a maximum of 2 hours
after which time the generation rate should be returned to the original schedule. The 113
MW reserve requirement for Glen Canyon Dam translates to approximately 2,800 cfs of
flow in the river. When the balancing area controllers call for reserve generation from
Glen Canyon Dam, releases from the dam can exceed scheduled levels and have a
noticeable impact on the river downstream from Glen Canyon Dam. But these calls for
reserves are fairly infrequent and typically are for much less than the required level of
113 MW.
Current Inflow Forecasts and Model Projections
Over the next three months (May, June and July) the forecasted unregulated inflow
volume to Lake Powell is projected to be 650 kaf (27% of average), 650 kaf (24% of
average) and 300 kaf (27% of average), respectively. These percent of averages are all
based on the historic period from 1981 through 2010. Combining this forecast with the
April Water Supply Forecast and extending projections to the end of WY2012, the most
probable (i.e. 50% likely to be exceeded) unregulated inflow volume for WY2012 is
projected to be 5.57 maf (51% of average). Comparing this projected water year
unregulated inflow volume to the driest year on record (2002) in which the unregulated
inflow volume was only 2.64 maf (24% of average), water year 2012 will likely be very
dry, yet not nearly as dry as conditions were in 2002. The currently projected water year
unregulated inflow volume of 5.57 maf would rank as the 4th driest year on record since
the closure of Glen Canyon Dam (1963) but there is still uncertainty associated with this
projection so this ranking could move up or down depending on what happens during the
remainder of the water year. Recent analysis indicates that it is reasonably possible for
the actual unregulated inflow volume for water year 2012 to be as low as 4.9 maf (45% of
average) or as high as 6.5 maf (60% of average) depending on the precipitation patterns
over the next several months.
Based on the reasonable range inflow conditions that could occur this year, the annual
release volume from Glen Canyon Dam would be 9.463 maf. Under the most probable
inflow condition, the annual release volume is projected to be 9.463 maf and the
elevation of Lake Powell at the end of WY2012 is projected to be 3625.5 feet above sea
level. This elevation corresponds to a live storage volume of 14.35 maf (59 % of full
capacity). These projections are based on conditions in the May 24-Months Study
Upper Colorado River Basin Hydrology
Since water year 2005, hydrologic conditions in the Upper Colorado River Basin have
been near average with significant variability from year to year. The unregulated inflow
to Lake Powell, which is a good measure of the hydrologic condition in the Colorado
River Basin, has averaged a water year volume of 10.98 maf (101% of average (period
1981-2010)) during the period from 2005 through 2011. The hydrologic variability
during this period has been from a low water year unregulated inflow volume of 8.62 maf
(80% of average) in water year 2006 to a high water year unregulated inflow volume of
15.97 maf (147% of average) which occurred in water year 2011.
Overall reservoir storage in the Colorado River Basin has increased by over 8 maf since
the beginning of water year 2005 and this is a significant improvement over the drought
conditions during water years 2000 through 2004. On October 1, 2004, the beginning of
water year 2005, the total reservoir storage in the Colorado River Basin was 29.84 maf
(50.2% of capacity). On October 1, 2011, the beginning of water year 2012, the total
reservoir storage in the Colorado River Basin was 38.66 maf (64.8% of capacity). As of
May 9, 2012 the total reservoir storage in the Colorado River Basin was 37.07 maf
(62.2% of capacity).
Updated: May 10, 2012
Rick Clayton1