The federal government began a manmade flood Wednesday to help restore the Grand Canyon's ecosystem, shooting two arcs of water from the base of the Glen Canyon Dam in northern Arizona.
More than 300,000 gallons of water per second was being released from Lake Powell above the dam near the Arizona-Utah border — enough water to fill New York City's Empire State Building in 20 minutes, Secretary of the Interior Dirk Kempthorne said.
"This gives you a glimpse of what nature has been doing for millions of years, cutting through and creating this magnificent canyon," Kempthorne said after he pulled the lever releasing the water.
The water level in the Grand Canyon will only rise a few feet as a result of the three-day flood, which officials hope will restore sandbars on the Colorado River downstream from the dam.
Officials have created a manmade flood in the canyon twice before, in 1996 and 2004, as part of efforts to mimic natural cycles on the river.
Before the dam was built in 1963, the Colorado River was warm and muddy, and natural flooding built up sandbars that are essential to native plant and fish species. The river is now cool and clear, its sediment blocked by the dam.
The change helped speed the extinction of four fish species and push two others, including the endangered humpback chub, near the edge.
During this week's flood, flows in the Grand Canyon are expected to increase to 41,000 cubic feet per second for nearly three days — four to five times the normal amount of water released from the Glen Canyon Dam.
Scientists will conduct several experiments during and following this week's flood, including one that will document habitat changes and determine how backwater habitats are used by the chub and other fish, and one that will look at how higher water flows affect the aquatic food base.
Without spring floods to flush the system and help rebuild beaches and fish habitat, native species suffered even as non-native fish thrived. The shift helped speed the extinction of four fish species and push two others, including the endangered humpback chub, near the edge.
First artificial flood in '96
In 1996, the government staged the first artificial flood in the canyon, opening Glen Canyon Dam's bypass tubes for several days in an attempt to replicate natural cycles. The second test in 2004 taught scientists the importance of sand and sediment.
The dam traps almost all the sediment that once flowed down the river, which is why beaches and habitats have eroded. A good monsoon season can wash significant quantities of sand down the Paria and Little Colorado rivers, which empty into the big Colorado below the dam.
The flood will scour and reshape miles of sandy banks on the floor of the Grand Canyon.
What scientists and environmentalists want to see is what will happen to the fish and the canyon when the gates close at dam and the staged flood recedes.
Federal officials insist they have progressed with long-term plans to offset the effects of the dam on the river and the Grand Canyon. The chub, the fish at the center of much of the dispute, has recovered some of its lost numbers since the last flood. Scientists also think they better understand when to trigger future floods.
"Our ultimate purpose is to learn whether or not this is a viable strategy for creating sandbars and habitats for native fish," said John Hamill, chief of the Grand Canyon Monitoring and Research Center, part of the U.S. Geological Survey.
Activists want permanent plan
Environmental groups argue that the flood again delays long-term changes to the river's management, further jeopardizing the canyon's health. They want federal officials to permanently alter the dam's operation instead of repeating the same test, adopting a seasonally adjusted plan that better mimics nature.
Nikolai Lash, senior program director for the Grand Canyon Trust, a group that has long fought the government over its management of the dam, said the flood was hastily planned after the trust sued the government last year for failing to protect the river.
He said the experiment was purposely designed as a single test, even though most scientists think floods must occur regularly.
"They're trying to make it appear that they're doing something beneficial when they're just doing it for appearances," he said. "It's being manipulated to be a 'one and done,' even though we know that doesn't work."