PAGE, Ariz. — With the sound of a siren to warn anyone downstream, government officials opened the spigots at the Glen Canyon Dam on Monday afternoon.
It's an effort to right an environmental wrong, the beginning of a five-day artificial flood. It released a surge of water from Lake Powell and aimed it hundreds of miles downstream at the Grand Canyon.
"The goal is to protect one of the world's most treasured landscapes here along the Colorado River," said U.S. Interior Secretary Ken Salazar, who presided over ceremonies at the foot of the nation's second-highest dam and personally pushed buttons to release the water.
This is the fourth experimental flood in the past 16 years. It's meant to mimic, on a small scale, the tremendous floods that frequently ripped through the Grand Canyon before the Glen Canyon Dam was built.
When it was completed in 1964, the dam became a gigantic barrier, not just to water, but to the sediments that once washed down the Colorado River in enormous quantities.
The dam holds back 95 percent of the sediment that used to flow into the Grand Canyon, according to Utah State University professor Jack Schmidt. He's currently serving as chief of the Grand Canyon Monitoring and Research Center established by the U.S. Geological Survey.
Most of the trapped sediment settles to the bottom in the upper reaches of Lake Powell and is permanently blocked from moving downstream.
The goal of this week's high-energy flood is to scoop up sediment that's piled up below the dam, in the bed of the Colorado River. Roughly 500 million tons of silt and sand are resting underwater, 15 miles downstream, where the Paria River enters the Colorado River. It's enough sediment to bury a football field 230 feet deep.
"Presently, that sand does not really do any natural resource good," Schmidt said.
The hope is that the flood will flush the huge pile of sediment hundreds of miles downstream, restoring lost beaches and sandbars that are critical to the Grand Canyon's native plants and animals.
Schmidt expects the brief flood to make a significant improvement, if not a miraculous restoration of the canyon.
"It will always be different than the natural river before humans arrived here," Schmidt said. "It will never put the river back to what it looked like in 1955."
Environmental groups have long argued for long-term changes in the dam's operation.
"It is the sediment that has been critically important for the fragile habitats within the Grand Canyon," said Dave Nimkin of the National Parks Conservation Association.
Decades of controversy and lawsuits over the issue have more recently given way to compromise, scientific studies and revised government management plans.
Scientific data gathered from three previous artificial floods, in 1996, 2004 and 2008, paved the way for a new 10-year protocol with a new policy direction.
"We're going to do these (flood) events every time we can," Schmidt said, "every time there's sediment available downstream."
Such policy changes require a delicate balancing act. Tinkering with outflows from the dam to create environmental benefits inevitably leads to financial impacts elsewhere.
Government officials say they have to maintain the dam's value in storing huge amounts of water belonging to seven states. And Glen Canyon's powerhouse uses the stored water to generate electricity for millions of people in the West.
Still, government officials say they're moving toward a better balance.
"We're providing greater protection for downstream resources in one of the crown jewels in our national park system," said Anne Castle, Assistant U.S. Secretary of the Interior. "And we're doing that while continuing to provide water and power to all of our fellow citizens that live in the west."
There are battles yet to come, however.
The beneficial effects of the three previous floods washed away in a matter of months, according to Nimkin, because of the way the dam operates year-round.
"The standard way that water is released washes that all away," he said.
Nimkin said there may have to be changes in the daily operations of the dam to reduce its flushing effects on the Grand Canyon.
Schmidt agrees that this week's flood will not put the controversies to rest.
"There are huge amounts of decisions yet ahead," he said.
Government officials say this week's flood won't affect the level of Lake Powell in the long run. The lake's surface will drop about 2 feet this week, but officials plan to make adjustments later to cancel that out.
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