High-Flow Experiments from Glen Canyon Dam are the Colorado River's artificial floods — timed pulses meant to rebuild sandbars downstream in Grand Canyon. Under the LTEMP framework, 2025 and 2026 were supposed to be active HFE years. Instead, appropriations chaos and a lack of interagency consensus cancelled both the fall 2025 and spring 2026 experiments, rolling sediment accounting into a possible fall 2026 window.

The short version

• HFEs are controlled high releases from Glen Canyon Dam designed to move tributary-delivered sand onto eddy sandbars in Marble and Grand Canyons — the main tool managers still have for beach-building under post-dam sediment starvation.
• The 2024 LTEMP Supplemental EIS Record of Decision created a year-long sediment accounting period beginning July 1, with sediment “rollover” if an HFE is not run.
• Bureau of Reclamation cancelled the fall 2025 HFE, citing the federal appropriations lapse / government shutdown uncertainty that constrained monitoring and staffing (decision letter dated October 31, 2025).
• Reclamation also announced no spring 2026 HFE, citing insufficient consensus from the collaborative planning team of Interior agencies and Basin States; sediment mass balance rolls into the next accounting period beginning July 1, 2026.
• Collaborative teams planned to reconvene in late summer 2026 for a possible fall 2026 HFE if sediment triggers are met.
• Last implemented HFE in the public LTEMP-era tally cited on Reclamation pages was a spring experiment in April 2023 (peak releases reported around the high-30,000 cfs range depending on source). No HFE ran in 2024–early 2026 under the cancelled windows.

Why the dam runs floods on purpose

Before Glen Canyon Dam, the Colorado carried huge monsoon sediment loads and built beaches naturally. After the dam, clear water released from Lake Powell erodes sandbars faster than most years can replace them. HFEs temporarily raise dam releases — commonly discussed in the ~31,500 to 45,000 cfs experimental band under LTEMP protocols — so available sand can be lifted onto bars.

That makes HFEs river-corridor infrastructure in the management sense: not a visitor bridge or a pipeline, but an operational tool that reshapes camping beaches, backwater habitat, and the archeology-adjacent sand mantle along the river. Cross-link river science gear at stream gauges and river monitoring and USGS scientific infrastructure. This page stays on the dam’s HFE decision machine.

LTEMP rules, rewritten in 2024

The Long-Term Experimental and Management Plan is the 20-year adaptive-management framework for Glen Canyon Dam operations under the Grand Canyon Protection Act. The 2024 LTEMP Supplemental EIS ROD changed how sediment is banked for HFEs: a year-long accounting period starting July 1, with the ability to roll unused sediment opportunity into the next period if no HFE is conducted.

That rewrite matters for 2025–2026. Cancelling an HFE no longer just “skips a season” in the old half-year Paria accounting logic — it explicitly carries sediment mass-balance into the next July 1 window. Reclamation’s public LTEMP page states that after the spring 2026 no-go decision, sediment rolls into the period beginning July 1, 2026, with fall 2026 reconsideration.

The 2025–2026 cancellation streak

Fall 2025: Upper Colorado Basin Regional Director Wayne Pullan’s October 31, 2025 letter told AMWG/TWG/Planning teams Reclamation would not implement a fall HFE, pointing to the appropriations lapse and uncertainty about resources needed to run and monitor the experiment. Modeling had suggested sediment conditions could support a later window; spring 2026 was flagged for reconsideration at that time.

Spring 2026: Reclamation later announced no spring 2026 HFE. The public rationale shifted from shutdown logistics to insufficient consensus among the collaborative planning team (Reclamation, NPS, USGS, FWS, BIA, WAPA, and the seven Basin States). Sediment rollover into the July 1, 2026 accounting period followed the 2024 ROD protocol.

Fall 2026: As of research date (2026-09-23), Reclamation’s LTEMP page said the collaborative team would reconvene in late summer 2026 to start planning for a possible fall 2026 HFE if triggers are met. That is a planning statement, not an approved hydrograph.

Separate LTEMP experiments (for example, cool-mix / smallmouth-bass flows discussed in Adaptive Management Program updates) are related dam ops but are not HFEs. Do not conflate them with beach-building floods.

What’s actually off-limits (and why)

HFEs themselves are not a park “closed area” — they are dam operations upstream of Lees Ferry. What visitors feel is downstream:

• River camps and sandbars — reshaped during/after HFEs; some camps become better, some scoured. Not a closure category, an ongoing geomorphic change.
• Dam tour / restricted Reclamation facilities at Glen Canyon — separate critical-infrastructure and security rules; HFE planning does not grant public access to powerplant decks or restricted dam zones.
• Why this matters for Grand Canyon pages: cancelled HFEs mean another year of net sandbar erosion risk under normal dam releases — a river-corridor infrastructure outcome even when no orange “closed” sign appears on a beach.

For park-side river corridor closures (confluence, cultural sites, etc.), see what is off-limits and individual river-mile dossiers. This page does not publish coordinates or access routes.

Sources

1. Glen Canyon Dam Long-Term Experimental and Management Plan - Bureau of Reclamation
2. Glen Canyon Dam Adaptive Management Program - Bureau of Reclamation
3. A 2025 Fall HFE - Glen Canyon Dam Adaptive Management Program
4. The HFE Page - Glen Canyon Dam Adaptive Management Program
5. Bureau of Reclamation Cancels Fall High-Flow Experiment at Glen Canyon Dam - Circle of Blue
6. Interior Department Releases Final EIS for Glen Canyon Dam Adaptive Management - U.S. Department of the Interior