Jeff Robbins, Associated Press
Glen Canyon Dam released water to boost sediment along the river in 1996.

Four majestic waterfalls erupted from Glen Canyon Dam on Sunday and roared into the foaming Colorado River. They are to continue blasting into the river for nearly four days.

"It looks like four very uniform waterfalls," said an eyewitness, interviewed by telephone. The woman, who did not wish to be identified in the newspaper, said that when peak flow begins, the columns of water should fly across the canyon and hit the other side of the huge dam.

At the greatest outflow, 41,000 cubic feet per second of water from Lake Powell blasts from the dam, racing down to the Grand Canyon. It is an experiment to see whether increased sediment levels sent downstream will help the survival of native fish and improve recreational beaches.

"We're very encouraged," U.S. Geological Survey director Chip Groat told the Deseret Morning News in a telephone interview from Phoenix, after he had attended the start of the experiment. "Today was a chance to build on what we learned in '96, when we had some pretty high-duration high flows."

In the trial in 1996, water thundered from the dam's bypass tubes for 7 days at 44,000 cfs. Peak flow this time will be 41,000 cfs, a level that should have been reached at 4 a.m. today. That rate will continue for 60 hours.

The earlier idea was a good one, Groat said. But when a high flow continues that long, it not only redeposits sediment, "it also starts to eat it up again and take it away," he said.

The waterfalls spouted from bypass tubes on the lower right side of the dam (as seen from below). They were shooting at an angle across the river, the woman interviewed Friday added.

"It's very impressive. The water is churning, like you would see at Niagara Falls or a substantial waterfall," she said.

Flows that are higher than the capacity of power generators at the dam, located at Page, Ariz., are being used. They are believed to be fast enough to pick up and move sediment that accumulated below the dam in Marble Canyon at the confluence of the Paria and Colorado rivers.

If all goes well, sediment will sweep downriver into the Grand Canyon, where it will rebuild beaches and improve habitat for fish.

In addition, a project began in January 2002 to remove fish not originally from the region, which also would boost the chances of such native fish as the endangered humpback chub. Many of the invaders are of the salmonid variety, such as trout, that feed on native fish. They were taken by electroshocking the water and then netting trout and carp that surfaced.

The project was proposed by the U.S. Bureau of Reclamation, managers of Glen Canyon Dam; the National Park Service, which runs Glen Canyon National Recreation Area, encompassing Lake Powell, as well as Grand Canyon National Park; and the USGS, which operates the Grand Canyon Monitoring and Research Center, based in Flagstaff, Ariz.

According to an environmental assessment posted by the Bureau of Reclamation, the purposes of the project are "(1) to contribute to the conservation of endangered native fish, especially the humpback chub, by reducing populations of non-native fish who compete with and prey on native fish between Glen Canyon Dam and Lake Mead; (2) to conserve fine sediments that form sandbars, beaches and habitat for young native fish by altering dam operations; and (3) to improve the Lees Ferry sport fishery by reducing the overabundance of trout."

For the next year and a half, scientists from government agencies and universities will use on-site surveys and fly-overs to map the redistribution of sediment. They will sample water and test it by laser to measure the amount of silt.

The studies may help redesign outflows from the dam to better preserve and restore the region downstream, according to a press release by the bureau.

"Aerial photography will be complemented by channel-bed mapping and sediment classification," it adds. Remote sensing projects will start around Memorial Day 2008. Another set of checks 18 months from now will track changes in the river.

Meanwhile, the dam is putting on a spectacular show. "Big dams and lots of water coming of tubes in the bottom is always impressive," said Groat.

What's more encouraging, he said, is knowing that the experiment may improve the management of the river.