April 2023 High-Flow Experiment


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B-roll Video: unedited footage of the start of the 2018 High Flow Experiment showing the river outlet tubes being opened at the beginning of the event.

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4 minutes, 33 seconds

B-roll Video: unedited footage. The goal of the High Flow Experiment (HFE) is to move sand stored in the river channel and redeposit it to rebuild eroded sandbars and beaches downstream of the Paria River in Grand Canyon National Park. This footage is from a HFE that took place between November 5-10, 2018, when the Department of Interior increased the release of water from Glen Canyon Dam for an HFE of approximately 38,100 cubic ft per second (cfs) for 3 days. https://www.nps.gov/grca/learn/nature/hfe-23.

Photo comparison of a sandbar below a cliff along the Colorado River. Top photo shows sandbar before the high flow; it takes up 1/5 of the width of the photo. The after photo shows a sandbar more that 1/2 the width of the photo
Sandbar at river mile 45 before (top) & after, the 2012 high-flow.

U.S. Geological Survey/Willie Taylor

April 24-27, 2023 – The Department of Interior (DOI), through the Bureau of Reclamation will conduct a High Flow Experiment (HFE) release from Glen Canyon Dam. The HFE will have a peak magnitude release of approximately 39,500 cubic feet per second (cfs) for 72 hours.

This experiment will involve a release of water from Glen Canyon Dam that is much larger than normal for approximately 4 days (including ramp up and ramp down). The experiment is designed to move accumulated sediment from the Paria River up onto beaches and sandbars in Marble Canyon and eastern Grand Canyon to restore the Colorado River corridor in eastern Grand Canyon National Park. Sandbars serve as camping beaches for recreationists, while also supplying sand needed to protect archaeological sites. Currently, high sediment loads and favorable hydrology conditions are present to support this experiment.

HFEs are implemented under the provisions of the Glen Canyon Dam Long-Term Experimental and Management Plan (LTEMP), which was formalized with a Record of Decision signed by the Secretary of the Interior in December 2016. The LTEMP operations and experiments assist the DOI in complying with the stewardship responsibilities of the 1992 Grand Canyon Protection Act. This HFE will not affect the total annual amount of water released from Lake Powell to Lake Mead.

The 1992 Grand Canyon Protection Act directs the Secretary of the Interior to manage Glen Canyon Dam in such a way as to “protect, mitigate adverse impacts to, and improve the values for which Grand Canyon National Park and Glen Canyon National Recreation Area were established.”


2023 Flow Information

Since 1996, releases from Glen Canyon Dam have generally ranged from 8,000 to 25,000 cfs. The increase in flow during the HFE to approximately 39,500 cfs will change conditions on the Colorado River. The HFE will change the river stage quickly during ramp up and ramp down phases. At higher flows, some normally difficult rapids might decrease in their technical difficulty, and other rapids might become more technically challenging. River runners are advised to scout rapids to check for new features, and ensure rapids are clear of boats or swimmers. River users should exercise caution along the Colorado River through Glen and Grand canyons during the entire week of April 24-30, 2023.

There are inherent risks associated with recreational activities along the Colorado River corridor through Grand Canyon at all times.

Chart: Detailing the release pattern for Glen Canyon Dam's High Flow Experiment
Chart: Detailing the release pattern for Glen Canyon Dam's 2023 High Flow Experiment.
Map detailing the High Flow routing through Grand Canyon, April 24 through 27, 2023 showing when the peak water flow arrives the critical monitoring sites: Lees Ferry, Little Co River, Phantom Ranch, National Canyon, Diamond Creek and Pearce Ferry.
High flow Routing and arrival times at critical monitoring sites in Grand Canyon and downstream of Glen Canyon Dam.

2023 High Flow Experiment Snapshot

Schedule and Duration

(all times Mountain Standard Time and not hour ending)

April 24 - 2:00 a.m. begin up ramp to powerplant capacity (~25,500 cfs) [8 generation units]
April 24 - 6:00 a.m. open bypass tubes (1 per hour)
April 24 - 9:00 a.m. reach full bypass (~39,500 cfs) and stay at peak release for 72 hours

April 27 - 9:00 a.m. end of bypass, begin down ramp to base releases
April 27 - 10:00 p.m. end of High Flow Experiment

Total duration: 3 days and 20 hours; 3 days (72 hrs) at peak release

Ramp Rates

Ramp up: 4,000 cfs/hr from 8,033 - 25,500 cfs, then 3,500 cfs/hr to peak (39,500 cfs)

Ramp down: 1,750 cfs/hr from 39,500 – 25,500 cfs, then 2,500 cfs/hr to 14,631 cfs

High Flow Experiment Release Details

Maximum total release: 39,500 cfs
Powerplant capacity: 25,500 cfs
River outlet tubes: 14,000 cfs
Hydropower generation units available: 8 (all units)
River outlet tubes: 4

Releases and Lake Elevation

Releases will range from 8,033 - 14,631 cfs prior to and after the HFE

Lake Powell elevation is projected to decrease by approximately 4 ½ feet over the course of the HFE. This HFE will not affect the total annual amount of water released from Lake Powell to Lake Mead.

cfs = cubic feet per second
cfs/hr = cubic feet per second per hour


High Flow Experiments (HFE) Below Glen Canyon Dam

are driven by weather, sediment inputs, and other resource conditions, in accordance with the Long-Term Experimental and Management Plan (LTEMP).

From April 24-27, 2023, DOI through the Bureau of Reclamation will conduct a HFE release from Glen Canyon Dam. The HFE will have a peak magnitude release of approximately 39,500 cfs for 72 hours (nearly four days including ramp up from baseflows to peak release and then ramp down to base flows) to move accumulated sediment downstream to help rebuild beaches and sandbars in eastern Grand Canyon.

The timing of the April 2023 HFE takes advantage of a short period of time in the calendar year 2023 where all eight generating units at Glen Canyon Dam are available for use, which enables a maximum magnitude (powerplant capacity plus use of the four bypass tubes) of 39,500 cfs.

Releases from Glen Canyon Dam will begin ramping up to full power plant capacity (approximately 25,500 cfs) on the morning of April 24th at 2:00 a.m. MST. At 6:00 a.m. April 24th, bypass tubes at Glen Canyon Dam will be opened and releases will continue to increase up to full power plant and bypass capacity (approximately 39,500 cfs) by 9:00 a.m. MST on April 24th. Releases will be maintained at peak release for three days (72 hours) and then begin ramping back down.

Releases will return to normal operations at about 10:00 p.m. MST on April 27th. April releases from Glen Canyon Dam prior to and after the HFE are expected to fluctuate between 8,033 and 14,631 cfs.

The decision to conduct this HFE was made after careful consideration of sediment resources as well as potential impacts to other resources downstream of Glen Canyon Dam. Consultation with basin states, American Indian tribes, federal and state agencies was conducted for the LTEMP and coordination and notification has occurred for this experiment. Input from the Glen Canyon Dam Adaptive Management Program stakeholders was part of the DOI’s decision to conduct the experiment.

High-flow experiments benefit the Colorado River ecosystem through Glen and Grand Canyons by moving sand in the river channel and re-depositing it in downstream reaches as sandbars and beaches. Those sandbars serve as camping beaches for recreationists, and supply sand needed to protect archaeological sites in the eastern Grand Canyon.

Current flow at Lees Ferry: https://waterdata.usgs.gov/usa/nwis/uv?09380000

The April 2023 HFE is unique as it will mimic the natural flow pattern of the Colorado River which would typically occur each spring during the runoff of snowmelt. The five HFEs that have been conducted since the HFE Protocol was initiated in 2012 have each occurred during the month of November (2012, 2013, 2014, 2016, 2018). The April 2023 HFE is intended to rebuild some of the beaches lost since the last HFE nearly five years ago.

Water-flow experiments at Glen Canyon Dam do not change or impact the total annual amount of water released from Lake Powell to Lake Mead.

Sample campsite map shows projected high flow water level covering a beach often used for camping. The high flow level is indicated by a bright green overlay.
River users and backpackers can use these maps to determine which campsites provide the most camping area during the high flow.

Camp on Durable Surfaces

Because the river will be carrying a greater volume of water than usual, the high-flow experiment will also change the size and availability of campsites along the Colorado River. Most campsites will be smaller, and some particularly low lying campsites may not be usable. The Grand Canyon Monitoring and Research Center has maps of campsites showing modeled shorelines at 41,000 cfs available online at: https://usgs.maps.arcgis.com/apps/webappviewer/index.html?id=721001c63d91458883340f05c68c55f4

A wealth of additional information is available here:

The area available for camping will be smaller at most sites, and river users and backpackers may have to set up tents closer to one another than they would during typical flows. It is important to follow Leave No Trace principles and travel and camp on durable surfaces during this high-flow experiment. Durable surfaces include bare sand above the high flow line, sites where people have previously camped and established trails.

Beneath a canyon wall, a sandy area with mesquite, catclaw acacia, and netleaf hackberry growing in patches.
Please do not camp in the pre-dam old high-water zone.


Please Do Not Establish Camps in the Pre-dam Old High-water Zone

which is marked by mesquite, catclaw acacia, and netleaf hackberry on rounded sandy slopes or higher sand terraces.

The old high-water zone is especially fragile because it no longer receives moisture, sand or nutrients from natural annual floods that reached over 100,000 cfs prior to the construction of Glen Canyon Dam and is not replenished by experimental high flows.

Damage to root systems from soil compaction and erosion and to biological soil crusts by camping or social trails may be irreversible due to the extremely fragile nature of the old high-water zone.

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"It’s really important that you identify the historic high water line and encourage your entire group to camp below it."


View more chapters of the park's Non-commercial River Trip Orientation Video here or on YouTube

River users and backpackers are encouraged to communicate with each other about available campsites in order to protect the canyon's resources and to ensure a quality experience for everyone in the river corridor during the high flow and for those who follow.

Looking down from Glen Canyon dam during 2012 HFE with tubes open.
Dam tubes open during 2012 high-flow.

Bureau of Reclamation

Long Term Experimental and Management Plan (LTEMP)

The LTEMP provides a framework for ongoing experiments and management actions, including a framework for using dam operations to release high flows following tributary deposits of new sand into the main channel of the Colorado River. It was developed by the Department of the Interior pursuant to the National Environmental Policy Act based on the best available scientific information developed through the Glen Canyon Dam Adaptive Management Program and other sources of information.

The HFE builds on a wealth of scientific knowledge gained from more than two decades of extensive scientific research, experimentation, and analysis, including analysis of a series of previous high-flow experimental releases in 1996, 2004, 2008, 2012, 2013, 2014, 2016, and 2018. The HFE and other actions in the LTEMP are intended to provide additional data essential to inform and refine future management decisions for the management of the Colorado River through 2036.

Beneath canyon walls, a river makes a bend around to a large sandbar where boaters are camping. 6 rafts are tied to the shore an several tents are set up on the sand.
Sandbar on the Colorado River in Grand Canyon being used as a camping spot.

USGS/Scott VanderKooi

This experiment will help scientists and managers better understand how higher flows created by releasing water from Glen Canyon Dam can be used to rebuild eroded beaches downstream.

Colorado River sandbars within the Grand Canyon serve as camping beaches for recreationists, and supply sand needed to protect archaeological sites.


a poster showing the dam's bypass tubes open as the background
Download this poster as an accessible PDF file (1.03 MB)

Quick Links

Download the April 2023 High Flow Experiment Poster

  • Sized for printing on 11x17 paper.
  • 104 MB PDF file (508 compliant)

USGS Campsites map at 41,000 cfs river level
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Glen Canyon Dam 2018 High Flow Summary

View and download public domain photos of the 2018 High Flow Release on Grand Canyon National Park's Flickr site.

Last updated: April 20, 2023

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Grand Canyon, AZ 86023



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