Celebrate! A Spring High Flow Experiment in Grand Canyon
Last week, the Bureau of Reclamation announced the authorization of a spring High Flow Experiment (HFE) in the Grand Canyon. This is a big deal.
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.
What is an HFE?
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.
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.
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) and last into Thursday evening (April 27.) 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.
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!)