Glen Canyon Dam / Lake Powell
The unregulated inflow volume into Lake Powell so far in February has been
somewhat below the forecasted level. As of February 21, 2010 the
unregulated inflow rate to Lake Powell is on pace to reach approximately
295,000 acre-feet for the month which would be about 30,000 acre-feet less
than what was forecasted at the beginning of February. The February 2010
24-Month Study projected that the end of month elevation of Lake Powell
would be 3619.97 feet above sea level. As of February 21, 2010 the
projected end of month elevation of Lake Powell is now 3620.19 feet above
sea level (about 2 inches above what was projected) which is about 2 feet
lower than the reservoir elevation on February 1, 2010.
Releases from Glen Canyon Dam during the month of February 2010 have
fluctuated each day for power generation between a peak hourly average
release of about 14,000 cubic feet per second (cfs), during the morning
and afternoon and a daily low hourly average release of 8,000 cfs during
the late evening and early morning hours.
For March, the release volume is projected to be 600,000 acre-feet. Daily
fluctuations in March are projected to have a peak hourly average release
each day of approximately 12,000 cfs and a daily low hourly average
release of approximately 6,000 cfs.
In addition to the daily fluctuation pattern, instantaneous releases from
Glen Canyon Dam also fluctuate to provide approximately 40 megawatts 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 88 megawatts
(approximately 2400 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 88 megawatts.
The mid-month Water Supply Forecast for February (April-July Unregulated
Inflow Volume) was reduced by 200,000 acre-feet from the official Water
Supply Forecast for February to 5.6 million acre-feet (maf) which is 71%
of average. This forecast will be updated during the first week of March
2010.
The February 2010 24-Month Study projected that the water year release
volume from Lake Powell will likely be 8.23 maf pursuant to the Interim
Guidelines. However, the operating tier for Glen Canyon Dam in water year
2010 is Upper Elevation Balancing and under this tier there is a
possibility for an April adjustment to the operational plan which could
incorporate either Equalization releases or Balancing releases. Given the
current conditions of Lake Powell and Lake Mead, it is possible, if
hydrologic conditions become wetter than what is currently projected, that
an April adjustment to Equalization could occur. If this adjustment were
to occur in April, the projected water year release from Glen Canyon Dam
could be greater than 10.5 maf.
As of early February, given the hydrologic conditions within the Colorado
River Basin and the range of possible inflow scenarios that could occur in
2010, Reclamation estimates that there is about a 25% probability that an
April adjustment to Equalization will occur. This estimate is based on
many factors that are changing through time. Reclamation will update this
estimated probability each month to provide stakeholders some indication
of the probability that Equalization will occur in water year 2010.
The February 2010 24-Month Study has been published and will be available
here:
http://www.usbr.gov/uc/water/crsp/studies/24Month_02.pdf
Updated elevation projections for Lake Powell through water year 2010
based on the most recently published 24-Month Study are maintained at:
http://www.usbr.gov/uc/water/crsp/studies/lppwse.html
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 the 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%.
The Climate Prediction Center outlook (dated January 21, 2010) for
temperature over the next 3 months indicates that temperatures in the
northern reaches of the Upper Colorado River Basin have an increased
probability of being above average. Accumulated precipitation over the
next 3 months are projected to be near average in the Upper Colorado River
Basin (above Lake Powell) while are projected to be above average in the
Lower Colorado River Basin (below Lake Powell).
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 February 9, 2010 the storage in
Lake Powell was 13.93 million acre-feet (57.29 percent of capacity) which
is still below desired levels while the overall reservoir storage in the
Colorado River Basin as of February 9, 2010 is 33.14 million acre-feet
(55.72 percent of capacity).
RRFW thanks Rick Clayton of the USBOR for his assistance in providing
information for this notification.
The unregulated inflow volume into Lake Powell so far in February has been
somewhat below the forecasted level. As of February 21, 2010 the
unregulated inflow rate to Lake Powell is on pace to reach approximately
295,000 acre-feet for the month which would be about 30,000 acre-feet less
than what was forecasted at the beginning of February. The February 2010
24-Month Study projected that the end of month elevation of Lake Powell
would be 3619.97 feet above sea level. As of February 21, 2010 the
projected end of month elevation of Lake Powell is now 3620.19 feet above
sea level (about 2 inches above what was projected) which is about 2 feet
lower than the reservoir elevation on February 1, 2010.
Releases from Glen Canyon Dam during the month of February 2010 have
fluctuated each day for power generation between a peak hourly average
release of about 14,000 cubic feet per second (cfs), during the morning
and afternoon and a daily low hourly average release of 8,000 cfs during
the late evening and early morning hours.
For March, the release volume is projected to be 600,000 acre-feet. Daily
fluctuations in March are projected to have a peak hourly average release
each day of approximately 12,000 cfs and a daily low hourly average
release of approximately 6,000 cfs.
In addition to the daily fluctuation pattern, instantaneous releases from
Glen Canyon Dam also fluctuate to provide approximately 40 megawatts 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 88 megawatts
(approximately 2400 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 88 megawatts.
The mid-month Water Supply Forecast for February (April-July Unregulated
Inflow Volume) was reduced by 200,000 acre-feet from the official Water
Supply Forecast for February to 5.6 million acre-feet (maf) which is 71%
of average. This forecast will be updated during the first week of March
2010.
The February 2010 24-Month Study projected that the water year release
volume from Lake Powell will likely be 8.23 maf pursuant to the Interim
Guidelines. However, the operating tier for Glen Canyon Dam in water year
2010 is Upper Elevation Balancing and under this tier there is a
possibility for an April adjustment to the operational plan which could
incorporate either Equalization releases or Balancing releases. Given the
current conditions of Lake Powell and Lake Mead, it is possible, if
hydrologic conditions become wetter than what is currently projected, that
an April adjustment to Equalization could occur. If this adjustment were
to occur in April, the projected water year release from Glen Canyon Dam
could be greater than 10.5 maf.
As of early February, given the hydrologic conditions within the Colorado
River Basin and the range of possible inflow scenarios that could occur in
2010, Reclamation estimates that there is about a 25% probability that an
April adjustment to Equalization will occur. This estimate is based on
many factors that are changing through time. Reclamation will update this
estimated probability each month to provide stakeholders some indication
of the probability that Equalization will occur in water year 2010.
The February 2010 24-Month Study has been published and will be available
here:
http://www.usbr.gov/uc/water/crsp/studies/24Month_02.pdf
Updated elevation projections for Lake Powell through water year 2010
based on the most recently published 24-Month Study are maintained at:
http://www.usbr.gov/uc/water/crsp/studies/lppwse.html
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 the 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%.
The Climate Prediction Center outlook (dated January 21, 2010) for
temperature over the next 3 months indicates that temperatures in the
northern reaches of the Upper Colorado River Basin have an increased
probability of being above average. Accumulated precipitation over the
next 3 months are projected to be near average in the Upper Colorado River
Basin (above Lake Powell) while are projected to be above average in the
Lower Colorado River Basin (below Lake Powell).
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 February 9, 2010 the storage in
Lake Powell was 13.93 million acre-feet (57.29 percent of capacity) which
is still below desired levels while the overall reservoir storage in the
Colorado River Basin as of February 9, 2010 is 33.14 million acre-feet
(55.72 percent of capacity).
RRFW thanks Rick Clayton of the USBOR for his assistance in providing
information for this notification.