An artificial flood does good in the Grand Canyon

With quick flicks of his Japanese calligraphy brush, Dave Rubin sends dry sand particles flying into the wind. He’s crouched in a four-foot-deep sand trench with a trowel in one hand, brush in the other, and the Colorado River flowing behind him. Dr. Rubin, a US Geological Survey senior scientist, leans back and studies the sand layers, trying to read their story – the tale of this year’s three-day high-flow experiment that thundered down the Grand Canyon.

The trench is dug into a bankside sandbar, a highly desirable feature of the Grand Canyon for habitat, archaeological preservation, and recreational camping. Sandbars once peppered this stretch of the river, but the closing of the Glen Canyon Dam in 1963 began trapping millions of cubic yards of sand that had nourished them. In the last 12 years, three high-flow experiments have tried to re-create the floods that used to deliver the sand. The most recent one was in March.

Now scientists have descended on the canyon to study the outcome using a host of technologies, from simple shovels to underwater scans of the riverbed. Their findings, and their resulting suggestions on how to restore the canyon’s diminished sandbars, will then be thrown into the caldron of river and canyon management, where 25 stakeholders weigh such things as the interests of electrical power and water against the need to preserve a natural wonder and endangered species. Close to $80 million has been spent in the last decade on sedimentology and hydrology research. Environmentalists say the need for restoration is losing out to the need for electricity and water.

The Glen Canyon Dam, built on the upstream northeastern edge of the Grand Canyon, fundamentally changed the relationship between the canyon and the Colorado River.

“Artifacts of the existence of the dam are the clear water, the cold water, and steady low flows,” says Jack Schmidt, a watershed sciences professor from Utah State University. The tamed river, devoid of sand (close to 98 percent is stopped by the dam), now erodes through the sandbars and carries the sediment into Lake Mead, where it’s trapped behind Hoover Dam. According to researchers, the new behavior of the river has led to narrower rapids, eroded beach­­es, invasion of nonnative vegetation, and the loss of native fish. The Colorado River now has nearly twice as many nonnative fish species (60) as native ones (32), with the humpback chub population declining from 10,000 in 1989 to 6,000 in 2006.

In 1988, three groups – the Grand Canyon Trust, the Wildlife Federation, and the Western River Guides Association – sued to force the first environmental impact study of the Glen Canyon Dam, 25 years after it was finished. This led to the passage of the Grand Canyon Protection Act of 1992. The study that resulted found that the dam was negatively affecting fish habitat and sediment resources in the canyon.

Any sediment that enters the river below the dam settles to the riverbed and slowly bounces along the bottom. Pre-dam, periodic large floods would lift the sediment above the low-flow waterline and form sandbars, says Professor Schmidt. Part of the new management plan was to restore sandbars and beaches through so-called high-flow experiments.

The March 2008 high-flow experiment was designed to move more than 1 million metric tons of Paria River sediment that could have otherwise dribbled downstream to the lake. For 60 hours, the jet-tubes at the base of the dam gushed around 41,500 cubic feet per second (cfs), 25,000 cfs higher than normally allowed.

Brad Warren, the Colorado River Storage Project manager at the Western Area Power Administration, which markets the power generated at Glen Canyon Dam, said the experiment has cost WAPA $4 million this year because it has had to purchase power to meet a contract – power that it could have generated from the water that bypassed the turbines.

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