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.
Without high flows, sand slowly makes its way downstream to Lake Mead. The high flow is intended to drive sediment up along the sides of the canyon and above the normal water level.
"It looks like we might have conserved 15 to 20 percent of the sand," Melis said of the recent release.
The sand is also important for protecting eroding archaeological sites. It is blown over the sites by spring winds, USGS reported.
Research teams will measure the sand formations, vegetation, chub food supplies and other indicators to further evaluate the success of the experiment over the next 18 to 24 months, according to Andrea Alpine, director of the USGS Southwest Biological Science Center in Flagstaff.
"Doing that kind of big release is an important exercise to restore the natural conditions as best they can at the Grand Canyon," said David Nimkin, southwest regional director of the National Parks Conservation Association in Salt Lake City, an organization that advocates for national parks.
The bigger question will be how the Bureau of Reclamation uses what the scientists learn in plans for managing water flows in the canyon, he said. "We're anxious, we're interested, and we're appreciative of the scientific inquiry," he added.
The next high flow release is planned for 2012.
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Larry O'Hanlon's blog: Earth Impacts
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