Dam to unleash simulated flood

Environmentalists have complained for years that the Colorado River below a man-made dam was washing away natural sediment in the Grand Canyon, wiping away beaches and native fish and plants.

Today, a simulated flood will allow scientists to see whether the Glen Canyon Dam — the root cause of many of the problems — can also help fix them.

Officials plan to release a controlled flood, opening four giant steel tubes at the base of the dam and sending a torrent down the Colorado and into the canyon. An estimated 800,000 metric tons of sediment will be stirred up during its 90-hour run.

"We're trying to mimic the role of all that sediment that used to be there before the dam," said Dennis Fenn, director of the Southwest Biological Science Center, under the U.S. Interior Department.

Glen Canyon Dam, built 40 years ago upstream from the Grand Canyon, forever altered the landscape. Four of the canyon's eight native fish species have disappeared and prospects for the fifth, the endangered humpback chub, are grim.