Celebrate! A spring high flow experiment in #GrandCanyon — @AmericanRivers #COriver

Rafts in the Grand Canyon | Photo Amy S. Martin

Click the link to read the article on the American Rivers website (Sinjin Eberle):

Last week, the Bureau of Reclamation, the federal government agency that oversees and manages operations on the Colorado River, announced the authorization of a spring High Flow Experiment (HFE) in the Grand Canyon. This is a big deal since the last time an HFE was conducted was in the fall of 2018, and the last time a spring HFE was executed was in 2008. And with the COLORADO RIVER IN THE GRAND CANYON NAMED AS AMERICA’S MOST ENDANGERED RIVER® just last week, we are thrilled that this action is happening to benefit the ecosystem in the canyon.


A High Flow Experiment is in essence a simulated flood being conducted through Glen Canyon dam. In practice, the dam releases a high volume of water, usually through both the hydropower turbines and the bypass tubes, which are lower-elevation tubes through the dam that are usually only used for these short duration floods or in other unique situations (like releasing water during the extreme inflows of 1983) over a limited period of time. HFE’s are extremely important to the management of sand in the canyon and the healthy functioning of the Grand Canyon riparian ecosystem overall.

To set the stage even further, let’s go back to the time before the creation of Glen Canyon Dam. The Colorado River traditionally carried millions and millions of tons of sediment down the river each year. Since Glen Canyon was built, most of that sand has been trapped in the upper reaches of Lake Powell – as flows slow down as the river becomes the lake, the sediment drops out and settles (up near Hite and Halls Crossing and then the San Juan as it enters the lake as well.) The result is that the water coming through Glen Canyon dam is very clear, lacking the traditional sediment that would be carried by the river and maintaining beaches and sandbars and the natural ecological benefits of that silty, sediment-laden water throughout the canyon. This clear water erodes sand from beaches and sandbars, and for decades in the 1970’s and 1980’s was causing real problems with the canyon’s ecology. In the 1990’s and early 2000’s, some experiments were conducted to begin to learn how these floods might act and how they might contribute to sand and other ecological functions within the canyon. Then, in 2016, the Long Term Experimental and Management Plan (LTEMP) was completed and set the guidelines for how and how frequently future HFE’s could be conducted.

Now, the Paria River, which is about 17 miles downstream from Glen Canyon dam (and about a mile below the put-in at Lee’s Ferry) is the main source of sediment into the Grand Canyon. When the Paria River flashes (most commonly during the summer monsoon season) it can deposit tons of sand – sometimes more than a million tons of sand – in a summer. This sand is what can be pushed downstream in an HFE to rebuild beaches and sandbars, and aid in the protection of cultural resources throughout the length of the canyon.

The author preparing to measure the volume of sand at this Grand Canyon beach using geodetic survey techniques | Photo by Katie Chapman

One of the elements within these LTEMP guidelines is how and when these HFE’s may be conducted, and how often the program should try to make them happen. Sadly, they have not happened often enough, and the canyon is really suffering because of it. Since the last HFE in 2018, there have been complications with declining water levels across the basin but felt most acutely in Lake Powell as elevations have declined to record lows. Then in 2021 and 2022, the monsoons delivered abundant sand through the Paria into the Colorado River, but unfortunately also caused a lot of erosion of beaches downstream as these monsoon storms ripped across Grand Canyon and the Colorado Plateau.

Today, we are celebrating the decision by the Bureau of Reclamation to use this opportunity to trigger one of these HFE’s to move the volume of sand currently sitting near the mouth of the Paria to rebuild beaches and sandbars, repair the ecology, and aid the protection of cultural resources downstream.

Glen Canyon Dam | Photo courtesy of National Park Service

Reclamation was able to make this decision based on several factors. First, due to the drought operations conducted over the past two years, there is a good amount of water parked in Lake Powell to protect the hydropower infrastructure at Glen Canyon dam that had to be moved downstream sometime this year. Second, the sand is there and the damage to the beaches in the canyon is glaring. Third, the water sitting in Lake Powell right near the dam (in an area above the dam called the “forebay”) is quite cold, which could aid aquatic species downstream. And lastly, there is a window of time where Reclamation and the hydropower providers can shift the timing of some needed maintenance at the dam to free up the opportunity to have all 8 hydropower penstocks and some of the bypass tubes available to actually conduct the high flows through the dam.

This week’s HFE will be pretty dramatic, both visually and scientifically. The flow will begin early Monday morning (April 24, 2023) and last into Thursday evening (April 27, 2023.) The dam will ramp up releases to 39,500 cubic feet per second (CFS) and hold that for 72 hours straight creating a flood that will flow all the way to Lake Mead over a period of about a week, rebuilding sandbars and beaches along the way (and giving rafters in the canyon an exciting ride!) One additional key point to understand is that HFE’s consume no net loss of water in Lake Powell – after the HFE occurs, Glen Canyon dam will release slightly less water than normal over a period of weeks, in order to make up that amount of water that is shot downstream, yet another benefit in the design in these critically important High Flow Experiments.

High Flow Experiment Pattern

Again, we applaud the Bureau of Reclamation, the scientists at USGS’ Grand Canyon Monitoring and Research Center, and everyone else who has been working hard to make one of these HFE’s happen for years. We are looking forward to seeing the great results that will come out of this event very soon.

(To learn more about the Grand Canyon’s history and ecosystem, check out our new STORY MAP, CAUGHT IN THE MIDDLE – we think you will love it!)

One thought on “Celebrate! A spring high flow experiment in #GrandCanyon — @AmericanRivers #COriver

  1. Dear Coyote Gulch,

    Thank you for sharing the exciting news about the upcoming spring high-flow experiment in Grand Canyon’s American River Corridor. As a nature enthusiast and advocate for the preservation of our natural resources, I am thrilled to hear about this initiative and its potential impact on the ecosystem. I wanted to express my appreciation for the information you’ve provided and offer some feedback.

    Your article highlights the importance of the spring high-flow experiment in the Grand Canyon, focusing on the positive effects it can have on the river ecosystem. The controlled release of water aims to mimic natural flood events, which historically played a crucial role in shaping the landscape and supporting the diverse flora and fauna of the area. By replicating these high-flow events, the experiment aims to restore and enhance the ecological health of the American River Corridor.

    I appreciate the comprehensive explanation you provide about the goals and objectives of the experiment. By reintroducing sediment, creating new habitats, and promoting the growth of native vegetation, this high-flow event has the potential to benefit not only the aquatic species but also the riparian and terrestrial ecosystems that depend on the river.

    Furthermore, your article addresses concerns regarding the potential short-term impacts on human activities and infrastructure, such as rafting trips and campsite availability. The inclusion of information about the coordinated efforts to minimize disruptions and communicate with stakeholders demonstrates the careful planning and consideration given to balancing the needs of both nature and recreational activities.

    I would like to commend you for emphasizing the importance of ongoing monitoring and scientific research during and after the high-flow experiment. This data will provide valuable insights into the effectiveness of the restoration efforts and help inform future management decisions. It’s encouraging to see a commitment to evidence-based decision-making and adaptive management in such conservation initiatives.

    Additionally, I would suggest providing information or resources for readers who might be interested in supporting or getting involved in similar initiatives. This could include links to relevant organizations, volunteer opportunities, or ways to contribute to the ongoing conservation efforts in the Grand Canyon and other natural areas.

    Overall, your article provides an informative overview of the spring high-flow experiment in the American River Corridor of the Grand Canyon. By highlighting the ecological benefits and the thoughtful approach taken to mitigate potential impacts, you raise awareness about the importance of such initiatives and the need to balance conservation with recreational activities.

    Thank you again for sharing this exciting news. I hope my feedback proves useful and contributes to the knowledge of your readers.

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