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Old 03-27-2016, 10:37 AM
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T Gunn T Gunn is offline
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Lees Ferry Water Flow Update 3/24/16

Glen Canyon Dam Update
March 24, 2016

CURRENT STATUS

The current snowpack above Lake Powell is 92% of average. The end of
February elevation and storage of Lake Powell were 3,594 feet (106 feet
from full pool) and 11.2 million acre feet (maf) (46% of full
capacity), respectively. The reservoir is declining and will continue to decline
until spring runoff begins to enter the reservoir. The unregulated
inflow to Lake Powell in February was 396 thousand acre feet (kaf)
(101% of average). The release volume from Glen Canyon Dam in February was
700 kaf.

CURRENT OPERATIONS

In March 2016, the release volume will be approximately 693 kaf, with
fluctuations anticipated between approximately 8,000 cubic feet per
second (cfs) and 14,000 cfs and consistent with the Glen Canyon
Operating Criteria (Federal Register, Volume 62, No. 41, March 3,
1997).
The anticipated release volume for April is approximately 665 kaf with
daily fluctuations between approximately 8,000 cfs and 14,000 cfs. The
expected release for May is 700 kaf with daily fluctuations 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 up to 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
releases when called upon to respond to unscheduled power outages or
power system emergencies. Depending on the severity of the system
emergency, the response from Glen Canyon Dam can be significant, within
the full range of the operating capacity of the power plant for as long
as is necessary to maintain balance in the transmission system. Glen
Canyon Dam currently maintains 27 MW (approximately 800 cfs) of
generation capacity in reserve in order to respond to a system
emergency even when generation rates are already high. System emergencies occur
fairly infrequently and typically require small responses from Glen
Canyon Dam. However, these responses can have a noticeable impact on
the river downstream of Glen Canyon Dam.

The operating tier for water year 2016, established in August 2015, is
the Upper Elevation Balancing Tier, with an initial water year release
volume of 8.23 maf and the potential for an April 2016 adjustment to
equalization or balancing releases. Based on the current forecast, an
April adjustment to balancing releases is projected to occur and Lake
Powell is currently projected to release 9.0 maf in water year 2016.
This projection will be updated each month throughout the water year.

INFLOW FORECASTS AND MODEL PROJECTIONS

The April to July 2016 water supply forecast for unregulated inflow to
Lake Powell, issued on March 2, 2016, by the Colorado Basin River
Forecast Center, projects that the most probable (median) unregulated
inflow volume will be 5.7 maf (80% of average based on the period 1981-
2010). The projected water year 2016 inflow is 9.0 maf (83%). The
forecast decreased by 1.0 maf since last month due to February
hydrologybeing abnormally dry. At this early point in the season, there is still
significant uncertainty regarding this year's water supply. The
April-July forecast ranges from a minimum probable of 3.8 maf (53%) to
a maximum probable of 8.0 maf (112%). There is a 10% chance that inflows
could be higher than the current maximum probable forecast and a 10%
chance that inflows could be lower than the minimum probable forecast.

Based on the current forecast, the March 24-Month Study projects Lake
Powell elevation will end water year 2016 near 3,607 feet with
approximately 12.0 maf in storage (51% capacity). Note that projections
of elevation and storage for water year 2016 have significant
uncertainty at this point in the season. Projections of elevation and
storage using the minimum and maximum probable inflow forecast, updated
in January, are 3,587 feet (10.5 maf, 43% capacity) and 3,642 feet
(16.3 maf, 67% capacity), respectively. Under these scenarios, 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, potentially in lower elevation and storage. The annual release volume
from Lake Powell during water year 2016 is projected to be 9.0 maf
under the minimum, most, and maximum probable inflow scenarios. There is a
chance that inflows could be higher or lower, potentially resulting in
releases greater than 9.0 maf or as low as 8.23 maf in water year 2016.
The minimum and maximum probable scenarios will be updated again in
April.

UPPER COLORADO RIVER BASIN HYDROLOGY

The Upper Colorado River Basin regularly experiences significant year
to year hydrologic variability. During the 16-year period 2000 to 2015,
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 16 years. The period 2000-2015 is the lowest
16-year period since the closure of Glen Canyon Dam in 1963, with an
average unregulated inflow of 8.51 maf, or 79% of the 30-year average
(1981-2010). (For comparison, the 1981-2010 total water year average is
10.83 maf.) The unregulated inflow during the 2000-2015 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. The water year
2015 unregulated inflow volume to Lake Powell was 10.17 maf (94% of
average), which, though still below average, was significantly higher
than inflows observed in 2012 and 2013 (45% and 47% of average,
respectively). Under the current most probable forecast, the total
water year 2016 unregulated inflow to Lake Powell is projected to be 9.02 maf
(92% of average).

At the beginning of water year 2016, total system storage in the
Colorado River Basin was 30.0 maf (50% of 59.6 maf total system
capacity). This is nearly the same as the total storage at the
beginning of water years 2014 and 2015 which began at 29.9 maf and 30.0 maf,
respectively, both of which were 50% 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 2005. 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 total
Colorado Basin reservoir storage for water year 2016 is approximately 29.4 maf
(49% of total system capacity). The actual end of water year 2016
system storage may vary from this projection, primarily due to uncertainty
regarding the season's snowpack and resulting runoff and reservoir
inflow. Based on the January minimum and maximum probable inflow
forecasts and modeling, the range of end of water year 2016 total
system capacity is approximately 27.4 maf (46%) to 34.1 maf (57%),
respectively. The minimum and maximum probable scenarios will be
updated again in April.

This update courtesy of Paul Davidson, Bureau of Reclamation
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