Scientists flood the Grand Canyon to restore sandbanks and save endangered wildlife

A man-made flood is roaring through the Grand Canyon in a bold experiment to restore the sandbanks of the Colorado river and to save fish and plants that have been disappearing over the past 40 years.

A man-made flood is roaring through the Grand Canyon in a bold experiment to restore the sandbanks of the Colorado river and to save fish and plants that have been disappearing over the past 40 years.

The water is being channelled into the river and down the canyon through four giant steel pipes, carrying badly needed natural sediment with it. The $3.7m (£2m) venture, supported by more than a dozen US government agencies and groups, ends tomorrow, but how well it works will not be known for months.

About 50 scientists have already begun rafting down the river to study the immediate effects of the experiment and will continue to monitor it for the next 18 months.

Campers have been warned to stay away because their campsites may be flooded in the 90-hour operation.

An estimated 800,000 tons of sediment are expected to be stirred up by the torrential water flow of 41,000 cubic feet a second. It is hoped the sediment will recreate the sandbars, backwaters and beaches needed by fish, birds, snakes and plants that are dying out.

Four out of eight fish native to the Grand Canyon have already become extinct and prospects for the fifth, the humpback chub, are grim.

For thousands of years melted snow carried vast amounts of sand downstream, creating bars, backwater channels for spawning fish and sandy habitats for land animals. More recently it has provided beaches for rafters and fishermen.

But in 1963 the natural flow of sand and water was permanently altered by the construction of Glen Canyon dam, just upstream from the Grand Canyon. The dam now traps all the sediment that would have flowed through the canyon, leaving the Colorado river sand-starved and flowing with ice cold, crystal clear water used to generate electricity.

Native fish, which evolved in warm, silty waters, are disappearing and their young are eaten by cold-water trout that now dominate the river. Riverbanks have eroded and those that remain are choked with non-native vegetation. Other species that need the sediment deposits to survive include the south-western willow flycatcher, which eats vegetation that grows in sediment, and the Kanab amber snail, which lives in the vegetation.

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

The timing is believed to be ideal because torrential rain in October swept sediment into Glen Canyon dam, and scientists are now acting quickly to release the estimated million tons of sediment into the canyon before it settles.

"The ecosystem has been compromised by the dam and this is an effort to mimic what nature doesn't have a chance to do," said a Geological Survey spokeswoman. "This is an experiment and if it works out we are likely to consider more releases over the next 18 months. This is just the start."

A similar experiment in 1996 over 18 days was unsuccessful because it was based on faulty assumptions; but scientists are optimistic the latest venture, which has been planned differently and is taking advantage of new equipment, will have an almost immediate effect and some places along the river might build sandbars in as little as 13 hours.

"The goal is to throw as much sand as you can on to the sandbars without pushing more sand downstream than you need to," said David Rubin, a sediment expert at the US Geological Survey.

Bennett Raley, the assistant secretary for water and science at the Department of the Interior, said the experiment was a process by which scientists try something, learn from their mistakes and then try something else.

"Speaking tongue in cheek, playing God is harder than it looks," he said.