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Water Gush at Grand Canyon Has Mixed Results

Jessica Marshall, Discovery News

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Blasting Grand Canyon's Shores

April 8, 2008 -- After hurtling torrents of water down the Grand Canyon to test the ability of high flows to restore beaches and sandbars along the Canyon's riverbank, U.S. Geological Survey researchers report the effort had mixed results.

On Monday the USGS made public the first findings from its March 5 high flow test, in which it blasted approximately 41,500 cubic feet per second of Colorado River water through the Glen Canyon Dam into the Grand Canyon below for a period of 60 hours.

While environmental groups argue for these routine high flows to mimic the seasonal water flow patterns that existed before the dam was built in 1963, the dam generates enough cheap hydroelectric power to completely supply up to 1.3 million homes. The high flows cost the regional energy supply millions in lost power.

So far it appears the costly release was somewhat effective in restoring sand habitats.

The agency provided time-lapse videos taken along the river over the last 30 days at locations three and 45 miles below the dam. The videos show the water levels rise and fall at both locations while the shoreline sand formations change. At the site three miles downstream, the video reveals a beach area eroding following the release. At the mile-45 location, a sandbar develops from the surge.

"It's just impossible at this point to say whether it was a net positive or a net negative," said Ted Melis, deputy chief of the USGS Grand Canyon Monitoring and Research Center in Flagstaff, Ariz.

Not every downstream site experienced a gain in sand along the shoreline, Melis said. "It's a complex response, and it's not simply a matter of all winners and all losers."

The only source of sediment below the dam comes from tributaries dumping into the river below -- a more than 90 percent reduction from before the dam was built in 1963. The scientists are trying to determine whether this sediment combined with periodic high flows is enough to form beaches and the habitats they support, including the warm, calm backwaters believed to be rearing sites for the endangered humpback chub, one of four remaining native fish species in the canyon.

More than half of the backwaters appear to have grown or remained constant in size following the release, according to Melis's early estimate.

The government is required to protect the area under the Grand Canyon Protection Act of 1992, the Endangered Species Act, and other legislation. The Glen Canyon Dam permanently changed the once warm and muddy Colorado River into a cooler, clearer, tightly controlled water-delivery system.

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