Colorado snowpack powers simulated spring flood of Grand Canyon

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

Federal operators of the Glen Canyon Dam atop the Grand Canyon opened jets to begin this surge before sunrise Monday, sending what they described as “a pulse” of water whooshing through the Colorado River as it curves through the base of the canyon.

U.S. Bureau of Reclamation officials said they’ll maintain the surge until Thursday evening, ensuring a flow for 72 hours at 39,500 cubic feet per second of water.

This “High Flow Experiment” will require 270,000 acre-feet of water, federal officials said — enough to sustain 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 over an entire year for city supplies.

The water gushing out of dam jets this week normally would have flowed gradually over the month of April out of Lake Powell into the river. Eventually, the water will end up in Lake Mead, the key supply for Arizona, California and Nevada.

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

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

Since 2018, federal dam operators have declined to release water for simulated flood surges due to long-term drought and anxieties around record-low reservoir water levels, linked by scientists to climate warming and aridification of the Southwest — transformations that have left Lake Powell and Lake Mead less than a quarter full. Yet the nation’s 1992 Grand Canyon Protection Act requires efforts to ensure ecological health in the canyon, and officials established a program that includes simulated floods.

Federal officials this week declined to comment as water surged.

Dry times across the Southwest, and higher temperatures that over the past two decades reduced overall annual water in the Colorado River, have forced federal dam operators to prioritize keeping as much as possible in Lake Powell. Simulated floods for ecological purposes in the Grand Canyon became a casualty.

Last week, the environmental advocacy group American Rivers declared the Colorado River the nation’s most “endangered” river due to a lack of flooding. This week, American Rivers leaders applauded the surge as “a critical step” toward reviving the Grand Canyon.

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

Clear, colder-than-natural water released from the dam atop the canyon year after year “is eroding sand off beaches every day. Aquatic life and vegetation depend on those beaches. Other side, it’s just a bunch of rocks and tamarisk,” Eberle said, referring to invasive shrubs that thrive and out-compete native species when dams lead to regularized water flows.

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

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

Denver Water “is supportive of the environmental flow program” in the Grand Canyon, utility manager Jim Lochhead said, lauding the effort by multiple agencies that “come together to shift water releases — not increase overall releases — in order to mimic spring hydrology through the basin, which helps to improve beaches, sandbars and aquatic habitats.”

In 1963, the construction of the Glen Canyon Dam atop the Grand Canyon disrupted essential natural processes and created Lake Powell. Sand and other sediments that for centuries moved downriver, scouring surfaces and creating beaches, suddenly were backed up on the reservoir side of that dam. And the regularized, steady flows of clear water, devoid of sediment, gradually are transforming the canyon.

During the simulated spring flood, U.S. Geological Survey scientists are monitoring the effects on fish populations and aquatic insects.

At the Grand Canyon Trust, officials devoted to protecting the river and canyon called on federal authorities to find a way to conduct future simulated floods — even during dry times.

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

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