Twin torrents of water unleashed from a dam coursed through the Grand Canyon on Wednesday in a flood meant to mimic the natural ones that used to nourish the gorge’s ecosystem by spreading sediment.

“This gives you a glimpse of what nature has been doing for millions of years, cutting through and creating this magnificent canyon,” Secretary of the Interior Dirk Kempthorne said after he pulled the lever releasing the water from the Glen Canyon Dam.

More than 300,000 gallons of water per second were being released from Lake Powell above the dam near the Arizona-Utah border, enough water to fill the Empire State Building in 20 minutes, Kempthorne said.

The water level in the canyon will only rise a few feet as a result of the three-day flood, but officials hope that will be enough to restore sandbars on the Colorado River downstream from the dam. 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 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 dam.

Scientists will conduct several experiments during and following the flood. One study will document habitat changes and determine how backwater habitats are used by the chub and other fish, and another will look at how higher water flows affect the aquatic food base.