The water release is part of an experiment by the Department of the Interior to replace sand bars and backwaters in the Grand Canyon, lost over the years because of dam-regulated water fluctuations, by moving sediment downstream.

The idea is based on a similar seven-day flush in 1996. In that case, however, beaches weren't so much created as moved downstream.

Scientists decided the best way to create beaches is to conduct shorter floods during certain times when high concentrations of sediment are naturally transported into the Colorado from tributaries such as the Paria River.

At a news briefing, Chip Groat, director of the U.S. Geological Survey, said recent storms in the Four Corners region that coughed about a million tons of sediment into the river about 15 miles downstream from the dam made the timing perfect.

The bypass tubes will remain open until 4 p.m. Wednesday and at its peak at 4 p.m. today, the flow will rush 41,000 cubic feet of water per second into the river.

The goal is to help native fish species, such as the humpback chub, regain a toehold in the river that has been lost over time to non-native species, such as trout, and to restore beaches that have been washed away.

It is a bid to restore the bottom of the canyon to something resembling its natural state before the dam's opening in 1962.

A coalition of scientists, including many from the USGS, U.S. Fish and Wildlife Service and National Park Service, will conduct a series of 20 experiments this week as they float down the river, said Dennis Fenn, director of the four monitoring areas of the Southwest Biological Sciences Center.

Fenn said the scientists involved in the latest project include different disciplines in biology and geology.

Archaeologists will also be part of the project, studying 400 prehistoric American Indian sites and the effects the banks and sand bars play in preserving the ruins.

Aerial technology will also help map topographic features in concert with conventional survey teams.

David Rubin, a USGS geologist who studied the results of the 1996 flood, said Sunday his team plans to study the river's sediment load using tools ranging from a simple water bottle to laser technology that can identify 32 different sizes of particles from 2.5 microns to half a millimeter.

mhavnes@sltrib.com

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Tribune reporter Joe Baird contributed to this story.