Glen Canyon Dam Update July 2013

Current Status

The unregulated inflow volume to Lake Powell in June was 939 thousand
acre-feet (kaf) (35% of average).  The release volume from Glen Canyon Dam
in June was 800 kaf.  The end of June elevation and storage of Lake Powell
were 3600.1 feet (99.9 feet from full pool) and 11.76 million acre-feet
(maf) (48% 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

Releases from Glen Canyon Dam in July are currently averaging approximately
14,000 cubic feet per second (cfs) with daily fluctuations between
approximately 10,000 cfs at nighttime and approximately 18,000 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 July 2013 is 847 kaf.

In August, the release volume will likely be about 800 kaf, with daily
fluctuations for hydropower between approximately 9,000 cfs in the nighttime
and approximately 17,000 cfs in the daytime.  In September, the release
volume will likely be about 600 kaf with daily fluctuations between
approximately 7,000 cfs and 13,000 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 1,200 cfs above or below the hourly scheduled
release rate.  Typically, fluctuations for system regulation are 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.

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.

Inflow Forecasts and Model Projections

The hydrologic forecast for Lake Powell for the April to July water supply
season projects that the most probable (median) unregulated inflow volume
will be 2.67 maf (37% of average based on the period 1981-2010).  The
April-July most probable forecast decreased from last month and the overall
water supply outlook remains significantly below average.  Based on the
current forecast, the July 24-Month study projects Lake Powell elevation
will decline approximately 13 feet from July to September and end the water
year at 3587.0 feet with 10.5 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.

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.  This July
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
3,574.97 feet and the Lake Mead elevation would be 1,105.73 feet. Therefore,
the 2014 Lake Powell operational tier is currently projected to be the
Mid-Elevation Release Tier with an annual release volume of 7.48 maf.
However, if hydrology should become slightly wetter than is currently
projected and the August 24-Month Study projects the January 1, 2014 Lake
Powell elevation to be more than 3,575.00 feet, the Upper Elevation
Balancing Tier will govern and the annual release volume from Lake Powell
will be 8.23 maf or possibly greater. Based on analysis of a range of inflow
scenarios, the current probability of realizing an inflow volume that would
result in the Upper Elevation Balancing Tier is slightly less than 50
percent.

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 4.43 maf (41% of average), which would be a second
below-average year in a row. 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 given observed inflows and current
forecasts, the current projected end of water year 2013 total reservoir
storage is approximately 22.6 maf (45% of capacity).

This update courtesy of Paul Davidson, Bureau of Reclamation