Water, silt flood Grand Canyon

GRAND CANYON NATIONAL PARK, Ariz. - Scientists flooded the Grand Canyon on Sunday to restore beaches and save fish and plants that have been disappearing since sediment-free water began flowing from a dam 40 years ago.

A torrent of gushing water raced down the Colorado River and into the canyon, carrying badly needed natural sediment with it, as four giant steel tubes at the base of Glen Canyon Dam were opened.

"The sediment, sand, mud and silt play an important role in the ecosystem," said Chip Groat, director for the U.S. Geological Survey.

An estimated 800,000 metric tons of sediment were expected to be stirred up during the 90-hour run. The release should reach a peak early today, when 41,000 cubic feet of water - enough to fill more than 11 semitrailer trucks - will be moving through the dam every second.

Four decades ago, before the dam was built, natural flooding built up backwaters, eddies and sandbars with silt distributed from the Colorado's tributaries.

The construction of Glen Canyon Dam upstream altered the canyon: Four of eight native fish species have disappeared and prospects for the fifth, the endangered humpback chub, are grim. Only about 7 percent of the sediment before the dam was built remains.

Twenty experiments will be conducted during the test, including archaeological, biological and hydrological studies.

About 50 scientists will study the immediate effects of the high flow test on the canyon today, when the waters are expected to swell the highest. A small group of researchers began rafting down the river Sunday.

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