UC-411

2.1.4.13 

VIA ELECTRONIC MAIL ONLY

Memorandum

To: Chief of Staff

Office of the Assistant Secretary for Water and Science

From Wayne G. Pullan

Chair, Glen Canyon Leadership Team

Secretary’s Designee to the Adaptive Management Work Group (acting)

Subject: Notification of Decision to Implement a Spring Flow Experiment at Glen Canyon Dam

On April 10, 2023, the Glen Canyon Planning/Implementation (PI) Leadership Team finalized a 

majority recommendation to implement a Spring Flow Experiment (2023 Experiment) at Glen 

Canyon Dam in April 2023. Eight entities recommended the Spring Experiment, and 7 entities 

abstained from making a recommendation. No members objected to the 2023 Experiment based on 

information contained within the PI Technical Team Report and Recommendation. 

The recommendation was developed and evaluated within the adaptive management framework and 

provisions of the 2016 Record of Decision (ROD) for the Glen Canyon Dam Long Term 

Experimental and Management Plan (LTEMP) Final Environmental Impact Statement (LTEMP 

ROD) concerning annual planning for flow-based experiments.

In accordance with the LTEMP, the Department may make the decision to conduct flow-based 

experiments (e.g., High Flow Experiments (HFE), Macroinvertebrate Production Flows, Trout 

Management Flows, and Low Summer Flows) at Glen Canyon Dam if it is determined that there are 

no unacceptable adverse impacts on other resource conditions. LTEMP states that “Prior to 

implementation of any experiment, the relative effects of the experiment on the following resource 

areas will be evaluated and considered: (1) water quality and water delivery, (2) humpback chub, (3) 

sediment, (4) riparian ecosystems, (5) historic properties and traditional cultural properties, 
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(6) Tribal concerns, (7) hydropower production and WAPA’s assessment of the status of the Basin 

Fund, (8) the rainbow trout fishery, (9) recreation, and (10) other resources.” Water Year 2023 was 

the sixth full year of implementing the process for annual experimental planning under the LTEMP 

ROD. For future experimental planning, the Department welcomes input from each of the 

Leadership Team members as to whether the current process or another process should be used to 

satisfy the coordination and communication requirements under the LTEMP ROD.

Traditionally Associated Tribes are notified at least 30 days in advance of planned experimental 

flows. On February 22, 2023, notification of the possible 2023 Experiment and offer for 

consultation was emailed to the Tribes and Parties to the LTEMP National Historic Preservation Act 

Section 106 Programmatic Agreement (LTEMP PA). A follow up letter was sent on March 29, 

2023. At this time, no requests for consultation regarding the potential 2023 Experiment have been 

received.

The LTEMP ROD specifies the representation requirements for planning experiments at Glen 

Canyon Dam and is based on past successful planning and implementation of flow-based 

experiments. The PI Technical Team includes technical representatives from the Bureau of 

Reclamation (Reclamation), the National Park Service (NPS), the U.S. Fish and Wildlife Service 

(FWS), the Bureau of Indian Affairs (BIA), the U.S. Geological Survey’s (USGS) Grand Canyon 

Monitoring and Research Center (GCMRC), Western Area Power Administration (WAPA), the 

Arizona Game and Fish Department (AZGFD), the seven Colorado River Basin States (States), and 

the Upper Colorado River Commission (UCRC). The PI Leadership Team is made up of decision 

makers from the same organizations.

The 2023 water year was an exceptional hydrological period for the Colorado River basin. High 

snowpack in the western United States was a welcomed change following multiple years of severe 

drought conditions. The low annual release volumes for the last year have also enabled the holdover 

of large amounts of sand in Marble Canyon, which in higher volume release years is quickly washed 

downstream. The 2023 Experiment takes advantage of that holdover sand and the new sand inputs 

from the Paria River from 2023 together with an anticipated large annual release volume of up to 9.5 

million acre-feet in water year 2023. Focused analysis on the implications of this 2023 Experiment 

showed that there is no exacerbation of the non-native fish issues in the Colorado River below Glen 

Canyon Dam. In fact, no unacceptable adverse effects to any LTEMP resources were revealed 

within the Technical Report for any resources by the Planning and Implementation Technical Team.

Though the sediment triggers outlined by LTEMP ROD were not explicitly met during the 

accounting window to implement a spring HFE, the unique hydrology and sediment conditions in 

2023 presented an exceptional opportunity to implement positive actions on the river, including 

compliance with the Grand Canyon Protection Act through a high flow action. Thus the 2023 

Experiment was proposed and then analyzed under a Supplemental Information Report (SIR), which 
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concluded that the 2023 Experiment is covered under the analysis of the LTEMP Final 

Environmental Impact Statement. This type of spring flow action has been promoted by many 

members of the GCDAMP for years and was planned and will be implemented in a similar manner 

as a LTEMP spring HFE. The analysis in the SIR was undertaken for this 2023 April Experiment 

and the unique current conditions. The analysis, including the expedited consideration by the 

LTEMP PI Team, does not set a precedent for future LTEMP implementation.

Within the LTEMP, fall HFEs were predicted to be conducted frequently (~3 out of every 4 years) 

and it has been four years since the most recent HFE was triggered and implemented (fall 2018), and 

no spring HFEs have yet to be triggered. LTEMP anticipated spring HFEs in "26%" of the years

covered under the 20-year period (i.e., 5 out of 20 years). The LTEMP anticipated proactive HFEs 

would occur in 10% of the years, so 2 out of 20. The GCDAMP is generally behind schedule for 

HFEs according to the above information, and sandbar condition in the Grand Canyon is currently 

poor owing to lack of HFEs and high monsoonal activity that has created gullies that make many 

sandbars inhospitable to camping. 

This 2023 Experiment will provide a renewal of Grand Canyon beaches, which are used by over 

25,000 visitors per year and have not been rebuilt since the last HFE in 2018. The 2023 Experiment 

creates progress towards a variety of LTEMP resource goals, including but not limited to the 

Sediment, Recreational Experience, Natural Processes goals.

Though there was majority support for the 2023 Experiment, support from Arizona and California 

was contingent upon the following qualifications:

Arizona (Department of Water Resources) and California support the 2023 Experiment recognizing 

the following: 

• There are unprecedented and unique water supply and dam operation opportunities on the 

Colorado River in Water Year 2023, such as delayed balancing releases and the need to 

release additional water withheld in Lake Powell under modified DROA operations;

• The total actual sand accumulation load upon implementation is ~2.5 million metric tons, and 

Upper Marble Canyon is projected to receive an additional ~200,000 to ~500,000 metric tons 

of cumulative sand load for an April 2023 Experiment by the end of the 2023 spring 

accounting window;

• Reclamation is projecting a total annual release between 9.0 to 9.5 maf from Glen Canyon 

Dam within the remainder of the 2023 Water Year;
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• The experiment is expected to have positive impacts on LTEMP downstream resources in the 

Grand Canyon; 

And conditioned upon the following:

• The experiment does not create precedent for future actions. Future actions will be limited to 

the express terms of the LTEMP ROD; 

• The expedited Planning & Implementation process and stakeholder review will be limited to 

this experiment and will not become a regular consultation tool;

• That monthly volumes for the remainder of the 2023 Water Year under a 9.0 to 9.5 maf 

release will not be significantly redistributed from the currently projected release patterns;

• This experiment will not result in lower Lake Powell reservoir elevations below the current 

projected May 1st elevation on May 1st of 2023;

• Pre- and post-experiment monitoring must occur to fully document and facilitate analysis of 

the effects of the experiment; and

• This support applies to Water Year 2023, and only to the extent that the experiment is within 

the scope and authority of the LTEMP ROD.

Based on the identification of high resource benefits by both the PI Technical and Leadership 

Teams, the determination of no unacceptable adverse impacts, and majority recommendation for the 

Department to implement a 72-hr duration Spring 2023 Experiment, I concur with the determination,

and I have decided to conduct a Spring Experiment for 72-hrs of peak duration beginning on April 

24. We will continue to work with our partners on future experimental flows and in the protection of 

the Grand Canyon and our most important resources. 

I am grateful to both the PI Leadership and Technical Teams for their dedication and commitment to 

the process for annual experimental planning and for your continued support of the Glen Canyon 

Dam Adaptive Management Program.

For the deaf, hard of hearing or speech impaired, please dial 7-1-1 to access the telecommunications 

relay system.
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Attachment: Final Technical Report and Recommendation Regarding a Spring Flow Experiment at 

Glen Canyon Dam, April 2023.

cc: Camille Calimlim Touton, Commissioner