RRFW Riverwire - Glen Canyon Dam Update - Mountain Buzz
 



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Old 10-24-2012   #1
 
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Flagstaff, Arizona
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RRFW Riverwire - Glen Canyon Dam Update

RRFW Riverwire - Glen Canyon Dam Update
October 24, 2012

Current Status

Releases from Glen Canyon Dam in October are averaging approximately 8,030 cfs (cubic feet per second) and are steady with no fluctuations for hydropower generation. The scheduled release volume for October is 494 kaf (thousand acre-feet). In September and October, as part of the 2008 FONSI (Finding of No Significant Impact), releases from Glen Canyon Dam will be steady for a steady flow experiment. 2012 is the last year of the 5-year steady flow experiment. The anticipated release volume for November is 600 kaf with fluctuations for power generation throughout the day consistent with the Glen Canyon Operating Criteria (Federal Register, Volume 62, No. 41, March 3, 1997). However, the release volume may be adjusted in the event of a High Flow Experiment. (see below).

This fall marks the first season under a multi-year High Flow Protocol announced earlier this year by Secretary Salazar. See the following link for more details:
Salazar Announces Improvements to Glen Canyon Dam Operations to Restore High Flows and Native Fish in Grand Canyon

Under this Protocol, high flow releases are linked to sediment input and other resource conditions below Glen Canyon Dam. Preliminary sediment estimates appear favorable for a high flow experimental release to occur during the period of November 18 – 25, 2012 should sediment and other conditions warrant.

Reclamation’s planning activities for the high flow release are focusing on an anticipated date of November 19, 2012 for the bypass release to begin; however, no final decisions on the dates, duration or amount of the release have been made. Dam operations to ramp up to powerplant capacity prior to the bypass event would begin on November 18. During the High Flow Experiment, total releases from Glen Canyon Dam at full bypass may reach approximately 42,000 cfs. The total experiment, including ramping, could last anywhere from one and a half to six and a half days. November releases from Glen Canyon Dam prior to and after the high flow experiment would fluctuate between 5,000cfs and 8,000cfs. As more information on the potential high flow release becomes available, that information will be updated here.

To view the most current reservoir elevation, content, inflow and release, click on:
Bureau of Reclamation - Water Operations Data: Elevation, Content, Inflow & Release for last 40 Days.

The unregulated inflow volume to Lake Powell in September was 104 thousand acre-feet (kaf) (25% of average). The release volume from Glen Canyon Dam in September was 481 kaf. The end of September elevation and storage of Lake Powell were 3621.6 feet (78.4 feet from full pool) and 13.93 maf (million acre-feet) (57.3% of full capacity). The reservoir elevation is now declining.

The water year unregulated inflow volume for 2012 was 4.91maf (45.3% of average), placing the 2012 as the third driest on record since the closure of Glen Canyon Dam in 1963. Only 2002 and 1977 were drier, receiving 2.64 maf and 3.53 maf, respectively. In terms of reservoir elevation and storage, Lake Powell reached its peak for water year 2012 on June 3rd at 3636.9 ft (63.1 feet from full pool) and 15.64 maf (64.3% of capacity), respectively. The peak elevation in 2012 was 24 feet below the 2011 peak elevation of 3660.9 ft.

Releases for Water Year 2012 totaled 9.466 maf. Pursuant to the 2007 Interim Guidelines, Lake Powell operated under the Equalization Tier in 2012. Due to the dry hydrologic conditions experienced in 2012, the Equalization release objective was 9.463 maf, which is 8.23 maf plus 1.233 maf (the Equalization release volume from 2011 that could not be achieved by September 30, 2011). Throughout water year 2012, Reclamation adjusted 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 Dam 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, the current probability of realizing an inflow volume that would trigger Equalization in 2013 is approximately 20 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 October are averaging approximately 8,030 cfs and are steady with no fluctuations for hydropower generation. The scheduled release volume for October is 494 kaf. In September and October, as part of the 2008 FONSI, releases from Glen Canyon Dam will be steady for a steady flow experiment. 2012 is the last year of the 5-year steady flow experiment.

The anticipated release volume for November is 600 kaf with fluctuations for power generation throughout the day consistent with the Glen Canyon Operating Criteria (Federal Register, Volume 62, No. 41, March 3, 1997). However, the release volume may be adjusted in the event of a High Flow Experiment. This fall marks the first season of a multi-year High-Flow Protocol, under which high flow releases are linked to sediment input and other resource conditions below Glen Canyon Dam. Preliminary analysis appears favorable for a high flow experimental release to occur during the period of November 18 – 25, 2012. During the High Flow Experiment, total releases from Glen Canyon Dam at full bypass may reach approximately 42,000 cfs. The total experiment, including ramping, could last anywhere from one and a half to six and a half days. In the event of a high flow experiment, releases from Glen Canyon Dam prior to and after the high flow experiment are anticipated to fluctuate between 5,000cfs and 8,000cfs.

In December, the release volume will likely be about 800 kaf, with fluctuations throughout the day from about 8,000 cfs in the early morning to about 16,000cfs in the early evening.

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). 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 43 MW of reserves (approximately 1,100 cfs) for this purpose. 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 outlook forecast for water year 2013 projects that the most probable (median) unregulated inflow volume will be 7.60 maf (70% of average based on the period 1981-2010). Based on this hydrologic outlook, the October 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 3608.52 (91.48 feet from full pool) and 12.582 maf (51.7% capacity), respectively.

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 and the release volume for 2013 could be greater than 8.23 maf. Based on analysis of a range of inflow scenarios, the current probability of realizing an inflow volume that would trigger Equalization in 2013 is approximately 20 percent.

Upper Colorado River Basin Hydrology

Since water year 2005, hydrologic conditions in the Upper Colorado River Basin have resulted in significant year to year variability. 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 10.22 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 7.60 maf (70% 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 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 29.8 maf (50% of capacity). On October 1, 2012, the beginning of water year 2013, the total reservoir storage in the Colorado River Basin was 33.9 maf (57 % of capacity).

RRFW thanks Katrina Grantz, US Bureau of Reclamation, for this information

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