Colorado’s large snowpack feeds a massive “pulse” of water that is pulled through the Grand Canyon

A huge amount of water flowing from the snowy mountains of Colorado into the depleted reservoir in western Lake Powell is coming out of pipes this week to feed a massive, simulated flood through the Grand Canyon — the first in five years to try to revitalize the canyon’s ecosystems the way nature once did.

Federal operators of the Glen Canyon Dam at the top of the Grand Canyon turned on the jets to begin that rise before sunrise Monday, sending what they described as a “pulse” of water rushing through the Colorado River as it meanders through the canyon floor .

U.S. Bureau of Reclamation officials said they would maintain the surge through Thursday evening, ensuring a 72-hour flow of 39,500 cubic meters per second of water.

This “High Flow Experiment” will require 270,000 acre-feet of water, federal officials said — enough to support more than half a million households for a year. By comparison, Denver Water typically captures 290,000 acre-feet of water, or more than 94 billion gallons, from rain and snow in Colorado during an entire year to supply the city.

The water gushing from the dam’s jets this week would normally have gradually drained in April from Lake Powell into the river. Eventually, the water will reach Lake Mead, the main supply for Arizona, California and Nevada.

Federal officials based their recent decision to allow simulated flooding on this year’s relatively heavy high-mountain snowpack along the headwaters of the Colorado River, which begins west of Denver near Grand Lake.

The latest snow survey data from the US Department of Agriculture this week showed snowpack in the upper Colorado River basin at 129 percent of the 1991-2020 norm. Federal hydrologists have estimated that 14.7 million acre-feet of water will flow this summer from Colorado, Wyoming and Utah into Lake Powell.

Since 2018, federal dam operators have refused to release water for simulated flooding because of the long-term drought and concerns about record low reservoir water levels scientists have linked to climate warming and the aridification of the Southwest — changes that they left Lake Powell and Lake Mead less than a quarter full. However, the National Grand Canyon Protection Act of 1992 requires efforts to ensure the canyon’s ecological health, and officials have established a program that includes simulated flooding.

Federal officials this week declined to comment as the water rose.

Drier times in the Southwest and warmer temperatures that over the past two decades have reduced the total annual water in the Colorado River have forced federal dam operators to prioritize keeping as much as possible in Lake Powell. Simulated ecological flooding in the Grand Canyon has become a casualty.

Last week, the environmental advocacy group American Rivers declared the Colorado River the nation’s most “endangered” because of its lack of flooding. This week, American Rivers leaders hailed the increase as “an essential step” toward revitalizing the Grand Canyon.

A dead fish is seen near shore at low water levels on April 12, 2023, at Lake Mead National Recreation Area, Nevada. (Photo by RJ Sangosti/The Denver Post)

“The damage to the ecosystems of the Grand Canyon has been substantial” over the past five years, said American Rivers spokesman Sinjin Eberle, describing the damage caused by the dams, which trap sand and other sediments essential to aquatic life and canyon habitat.

The clear, colder-than-natural water released from the dam at the top of the canyon year after year “erodes the sand from the beaches every day. Aquatic life and vegetation depend on those beaches. Otherwise, it’s just a bunch of rocks and tamarisk,” Eberle said, referring to the invasive shrubs that thrive and outcompete native species when dams lead to regulated water flows.

In Colorado, water policy officials declined to take a position on the simulated flood. But they recognized the environmental benefits of the canyon.

“The intent of this release is to lift existing sediment in the canyon and deposit it downstream,” said Michelle Garrison, the state’s representative on a federal stakeholder advisory group that is part of the Glen Canyon Dam Adaptive Management Program.

Denver Water “supports the environmental flow program” in the Grand Canyon, said utilities manager Jim Lochhead, praising the multi-agency effort that is “coming together to change water releases — not increase overall releases — to mimic the hydrology of spring through the pool, which helps improve beaches, sandbars and aquatic habitats.”

Glen Canyon Dam holds back the Colorado River water that forms Lake Powell, seen from the air on April 15, 2023, in Page, Arizona.  Aerial photography flight was provided by LightHawk.  (Photo by RJ Sangosti/The Denver Post)
Glen Canyon Dam holds back the Colorado River water that forms Lake Powell, seen from the air on April 15, 2023, in Page, Arizona. Aerial photography flight was provided by LightHawk. (Photo by RJ Sangosti/The Denver Post)

In 1963, the construction of Glen Canyon Dam at the top of the Grand Canyon disrupted essential natural processes and created Lake Powell. Sand and other sediments that for centuries had moved downstream, scouring surfaces and creating beaches, were suddenly backed up on the reservoir side of that dam. And regularized, constant flows of clear water, free of sediments, gradually transform the canyon.

During the simulated spring flood, US Geological Survey scientists monitor the effects on fish populations and aquatic insects.

At the Grand Canyon Trust, officials dedicated to protecting the river and canyon have called on federal authorities to find a way to manage future simulated flooding — even during dry periods.

“For a long time we gave priority to hydropower. We have long prioritized water users. The environment is always the last priority,” said Jen Pelz, the trust’s director of water advocacy. “We have to figure out how to balance competing interests in a way that honors the environment.”

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