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Current Dam Operations

 

(Last Updated: October 12, 2017)

 

Current Status

High-Flow Experiments (HFE) below Glen Canyon Dam are driven by weather, sediment inputs, and other resource conditions, in accordance with the Glen Canyon Dam Long-Term Experimental and Management Plan Record of Decision (LTEMP). 

 

When sediment conditions during the summer and fall meet specific thresholds as described in the LTEMP HFE Protocol, a fall HFE can occur.  Fall HFEs can be scheduled to occur anytime during the months of October and November.   In order to facilitate advance planning for a potential HFE this fall, the HFE technical team determined that October 9th was the latest date for which sediment inputs could be considered for a potential HFE this fall.  Grand Canyon Monitoring and Research Center (GCMRC) scientists and Reclamation modelers considered cumulative sediment inputs from July 1 through midnight October 9th. Based on these data it has been determined that there is not sufficient sediment to support implementing a high flow experiment (HFE) at Glen Canyon Dam during the fall 2017 planning window; therefore an HFE will not be tested this fall.

 

The unregulated inflow to Lake Powell in September was 196 thousand acre-feet (kaf) (48% of average).  The release volume from Glen Canyon Dam in September was 663 kaf.  The end of September elevation and storage of Lake Powell were 3,628.31 feet (72 feet from full pool) and 14.66 maf (60% of full capacity), respectively.  The water year 2017 unregulated inflow to Lake Powell was 11.90 maf (110% of average).  The water year 2017 release from Lake Powell was 9.0 maf.  The reservoir elevation peaked at 3,635.80 feet on July 11th and is now in its seasonal decline through the fall and winter months.

 

To view the most current reservoir elevation, content, inflow and release, click on: Lake Powell Data.
To view the most current reservoir elevation projections, click on: Lake Powell Elevation Projections.
To view the 2017 progession of snowpack above Lake Powell, click on Lake Powell Snow Chart.
To view the current inflow forecast relative to past inflows, click on Lake Powell Inflow Forecast


Current Operations

The operating tier for water year 2018 was established in August 2017 as the Upper Elevation Balancing Tier, with an initial water year release volume of 8.23 maf and the potential for an April 2018 adjustment to equalization or balancing releases.  Based on the current forecast, an April adjustment to balancing is projected to occur and Lake Powell is currently projected to release 9.0 maf in water year 2018.  This projection will be updated each month throughout the water year.  Reclamation will schedule operations at Glen Canyon Dam to achieve as practicably as possible the appropriate total annual release volume by September 30, 2018.

 

In October 2018, the release volume will be approximately 667 kaf, with fluctuations anticipated between about 8,300 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).  The anticipated release volume for November is 630 kaf with daily fluctuations between approximately 8,000 cfs and 13,700 cfs.  The expected release for December is 740 kaf with daily fluctuations between approximately 7,300 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 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.  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.

 

Inflow Forecasts and Model Projections

The forecast for water year 2018 unregulated inflow to Lake Powell, issued on October 1, 2017, by the Colorado Basin River Forecast Center, projects that the most probable (median) unregulated inflow volume next year will be 9.71 maf (90% of average).  There is significant uncertainty regarding next season’s snow pack development and resulting runoff into Lake Powell.  The forecast ranges from a minimum probable of 7.0 maf (65%) to a maximum probable of 17.5 maf (162%).  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 October 24-Month Study projects Lake Powell elevation will end water year 2018 near 3,631 feet with approximately 14.9 maf in storage (61% capacity).  Note that projections of elevation and storage for water year 2018 have significant uncertainty at this point in the season.  Projections of elevation and storage using the minimum and maximum probable inflow forecast are 3,612 feet (12.9 maf, 53% capacity) and 3,654 feet (17.7 maf, 73% 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, resulting in lower elevation and storage.  The annual release volume from Lake Powell during water year 2018 is projected to be 9.0 maf under the minimum and most probable inflow scenarios and 13.56 maf under the maximum probable inflow scenario.  There is a chance that inflows could be higher or lower, potentially resulting in releases greater than 13.56 maf or as low as 8.23 maf in water year 2018.

 

Upper Colorado River Basin Hydrology

The Upper Colorado River Basin regularly experiences significant year to year hydrologic variability.  During the 18-year period 2000 to 2017, 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 4 out of the past 18 years.  The period 2000-2017 is the lowest 18-year period since the closure of Glen Canyon Dam in 1963, with an average unregulated inflow of 8.76 maf, or 81% 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 2000-2017 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.  In water year 2017 unregulated inflow volume to Lake Powell was 11.9 maf (110% of average), the fourth year to be above average.  Under the current most probable forecast, the total water year 2018 unregulated inflow to Lake Powell is projected to be 9.71 maf (90% of average).

 

At the beginning of water year 2018, total system storage in the Colorado River Basin was 32.9 maf (55% of 59.6 maf total system capacity).  This is an increase of 2.2 maf over the total storage at the beginning of water year 2016 when total system storage was 30.7 maf (51%).  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 2018 is approximately 32.52 maf (55% of total system capacity). The actual end of water year 2018 system storage may vary from this projection, primarily due to uncertainty regarding this season’s runoff and reservoir inflow.  Based on the October minimum and maximum probable inflow forecasts and modeling, the range of end of water year 2018 total system capacity is approximately 30.06 maf (50%) to 35.47 maf (59%), respectively.