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Water unleashed from a dam coursed through the (1) Grand Canyon in a flood meant to mimic the natural ones that used to nourish the ecosystem by spreading sediment.
More than 300,000 gallons (1.1 million liters) of water per second were released from Lake Powell above the dam near the Arizona-Utah border.
That's enough water to fill New York City's Empire State Building in 20 minutes, said Interior Secretary Dirk Kempthorne after he pulled the lever releasing the water from Glen Canyon Dam, upstream from Grand Canyon National Park.
The water gushed from two of four giant steel tubes in parallel arcs into the Colorado River. By afternoon, water poured from all four tubes, creating a churning pool beneath the sheer, sandstone canyon walls rising hundreds of feet.
The water level in the Grand Canyon rose 2 feet to 15 feet (60 centimeters to 4.5 meters) in some places. After the flood ends , officials hope the water will leave behind sediment and restore sandbars as it goes back to normal levels. Officials have flooded the canyon twice before, in 1996 and 2004.
Before the dam was built in 1963, the 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.
Shrinking beaches have led to the loss of half the camping sites in the canyon in the past decade. Since Glen Canyon Dam was built, 98 percent of the sediment carried by the Colorado River has been lost, Grand Canyon National Park Superintendent Steve Martin said. Martin said manmade floods need to occur every time there's enough sediment to do so - about every one to two years depending on Arizona's volatile monsoon season.
Scientists will document habitat changes and determine how backwater habitats are used by the chub and other fish. Another study will look at how higher water flows affect the aquatic food base. ■AP
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