A 2026 Spring HFE

High Flow Experiment- Spring 2026

2026 Spring High Flow Experiment Snapshot

DOI Decision

DATE: June 5, 2026 
TO: AMWG, TWG, and Planning and Implementation Team Members
FROM: Wayne G. Pullan, Regional Director, Upper Colorado Basin Region, Bureau of Reclamation 
SUBJECT: Decision Regarding Spring 2026 HFE
Dear AMWG, TWG and Planning and Implementation (PI) Team Members,  
I am writing to notify you that Reclamation will not implement a spring High Flow Experiment (HFE) from Glen Canyon this month. This decision reflects the mixed support expressed by members of the PI Leadership Team. In accordance with the revised HFE protocol, the sediment mass balance will roll over into the next accounting period beginning July 1, 2026, and an HFE will be reconsidered for potential implementation in fall 2026. I would like to extend my sincere appreciation to the PI Technical and Leadership Teams, as well as the Grand Canyon Monitoring and Research Center (GCMRC), for their dedication and contributions in supporting a well-informed decision.  
Consideration of a cool mix flow remains pending, and we anticipate sharing a decision in the coming weeks. Thank you for your patience as we work through these important and complex issues.  
Wayne G. Pullan, Director  
Upper Colorado Basin Region  

Recommendation Summary

Based on the 2016 LTEMP Record of Decision (ROD) and 2024 LTEMP Supplemental Environmental Impact Statement ROD, the Glen Canyon Dam Planning and Implementation (PI) Technical Team has worked over the past several weeks to evaluate existing information and data in determining this recommendation regarding an HFE at Glen Canyon Dam.

The Planning and Implementation (PI) Technical Team recommends the PI Leadership Team consider recommending the implementation of a spring High-Flow Experiment (HFE) at 32,400 CFS for 12 hours as described in the attached Tech Team Report.

Key discussion topics of the Planning and Implementation Technical Team summarized by Reclamation:

The PI Technical Team understood the importance of conducting an HFE to rebuild sandbars as well as support several other LTEMP resources. The short-duration HFE proposed would also be a great learning experience for potential future HFEs at Glen Canyon Dam as it would be the shortest duration HFE since the protocol was developed. Finally, it was important that Reclamation made it clear that any water volume adjustments for an HFE be made within the month of June and that no water be taken outside of the current proposed DROA/6e adjustments.

The PI Technical Team’s recommendation regarding implementation of a spring 2026 HFE is based on a careful assessment of resources and best available science.

Background and Purpose of the Recommendation

The purpose of this memorandum is for the PI Technical Team to transmit a recommendation to the Glen Canyon Dam PI Leadership Team. Once the PI Leadership Team has provided a recommendation, this memo will be forwarded to the Department of the Interior (Department) in accordance with the LTEMP ROD (DOI 2016a). The PI Technical Team includes technical representatives from the National Park Service (NPS), U.S. Fish and Wildlife Service (FWS), Bureau of Indian Affairs (BIA), U.S. Geological Survey (USGS) Grand Canyon Monitoring and Research Center (GCMRC), Bureau of Reclamation (Reclamation), Western Area Power Administration (WAPA), Arizona Game and Fish Department (AZGFD), seven Colorado River Basin States (Basin States), and the Upper Colorado River Commission (UCRC).

In the fall of 2024, after evaluating the LTEMP resources using the best available science and discussions within the PI Leadership Team, most PI Leadership Team members recommended deferring to a spring 2025 HFE. One member recommended a fall 2024 HFE. In the spring of 2025, the PI Technical Team reevaluated the Sand Budget Model and determined that there was sufficient sediment to conduct a spring 2025 HFE. Due to the risks of disrupting -12 Mile Slough modifications, the Technical Team ultimately recommended not to implement in the spring of 2025. Accumulated sediment was rolled over to the next accounting period for possible consideration of a fall 2025 HFE. In the fall of 2025, the PI Technical team reevaluated the Sand Budget Model and determined that there was sufficient sediment to conduct a fall 2025 HFE. However, due to the lapse in appropriations and the uncertainty concerning the necessary resources for monitoring, the Department of Interior decided to forgo the fall HFE. Accumulated sediment was rolled over to the next accounting period for possible consideration of a spring 2026 HFE. The PI Technical Team incorporated the most current science and data and considered multiple issues with agency experts, as summarized below, in making this recommendation.

In the fall of 2025, critical elevations were predicted for water year 2026 (Most Probable 24-Month Study: September 2025). The Upper Basin Drought Response Operations Agreement (DROA) planning trigger (projections of Lake Powell Elevations less than 3525 ft. within 12 months under most probable hydrology) was met. The projected likelihood of hitting the Interim Guidelines (IG) Supplemental Environmental Impact Statement (SEIS) 6(e) trigger (DOI 2024a) increased in the winter months due to low snowpack in the Upper Colorado basin. The LTEMP SEIS 6(e) requires operational adjustments in the Upper Colorado River basin when Lake Powell is projected to drop below elevation 3525 ft within 12 months, triggering modified monthly release volumes rather than changes to the annual release. In April, IG LTEMP 6e triggers were met based on the latest April Colorado River Mid-term Modeling System (CRMMS) results presented on April 17, 2026. Based on the monthly volume adjustments in December 2025 and proposed volume adjustments in April 2026, Reclamation recommends consideration of a HFE in June 2026, using the current proposed release (~ 460 kaf) anticipated from June 2026 and not re-allocating water from other months. Any HFEs proposed in the spring of 2026 do not change annual flow releases.

The PI Leadership team will consider the PI Technical Team’s recommendation and develop a PI Leadership Team recommendation to be submitted to the Secretary of the Interior. The Secretary of the Interior or his Designee retains sole discretion to decide how best to accomplish operations and experiments in any given year pursuant to the LTEMP ROD and other binding obligations for Glen Canyon Dam.

Spring HFE and No HFE

Over the past several weeks the PI Technical Team considered two primary options: conducting a spring HFE or not conducting an HFE and reconvening the PI Team in fall 2026 to review and provide a recommendation for a fall HFE using the sediment accounting window from July 1, 2024 - November 30, 2026.

The spring HFE under consideration has a duration of 12 hours at a peak magnitude of 32,400 cfs. The duration of the spring HFE is subject to adjustments as more information is gained. Department of Interior will make the final decision on parameters surrounding the HFE if one is to be implemented.

If the PI Team recommends opposing the spring HFE or an HFE cannot be conducted, the PI Team would like the sediment to roll over into the fall accounting period to be considered for a fall HFE.

The PI Technical Team’s recommendation to conduct/not conduct a spring HFE was by a consensus/majority vote (Table 1). The PI Team identified the following resource concern as a significant reason to implement/not implement a spring HFE flow:

Table 1. Technical position of Planning and Implementation Technical Team members for consideration of a spring 2026 High-Flow Experiment.

Entity DOI-BOR Recommendation/Position Support DOI-NPS DOI-FWS Support Support DOI-USGS DOI-BIA Abstain No Vote DOE-WAPA Arizona Support Support California Colorado Abstain Support Nevada New Mexico Abstain Support Utah Wyoming Support Oppose AZGFD UCRC Support Oppose

Entity	Recommendation/Position
DOI-BOR	Support
DOI-NPS	Support
DOI-FWS	Support
DOI-USGS	Abstain
DOI-BIA	No Vote
DOE-WAPA	Support
Arizona	Support
California	Abstain
Colorado	Support
Nevada	Support
New Mexico	Support
Wyoming	Oppose
AZGFD	Support
UCRC	Oppose

Assessment of Resources consistent with the 2016 LTEMP ROD and 2024 LTEMP SEIS ROD (all resources were evaluated for a fall HFE)

Nonnative Invasive Species

Green Sunfish (Lepomis cyanellus)

Brown Trout (Salmo trutta)

Smallmouth Bass (Micropterus dolomieu)

Other Nonnative Invasive Fishes

SUPPORTING DOCUMENTS

• 2026 Spring HFE Tech Report

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