A River Run Through: USU Scientists Analyze Colorado River Experiments

After years of manmade diversions, the once-mighty Colorado River will never be the same.

That’s the blunt assessment of Utah State University researcher Jack Schmidt, USU alum Paul Grams and fellow team members who contributed to the U.S. Geological Survey report, “Effects of Three High-Flow Experiments on the Colorado River Ecosystem Downstream from Glen Canyon Dam, Arizona.”

Released by the USGS Feb. 8, 2011, the exhaustive report details findings from high-flow dam releases, each designed to mimic natural seasonal flooding, that were conducted in 1996, 2004 and 2008. Within the document, Schmidt and Grams summarize 15 years of study carried out by an army of researchers.

“There’s really no way we can expect to have a pre-dam landscape by implementing high flows,” says Grams, a hydrologist with the Grand Canyon Monitoring and Research Center, who earned a master’s degree from USU in 1997 and completed a postdoctoral appointment with Schmidt in 2008.

“The Glen Canyon Dam, constructed in 1963, traps sediment that used to form and replenish sandbars crucial to native ecosystems,” says Schmidt, professor in USU’s Department of Watershed Sciences and director of the USU-led Intermountain Center for River Rehabilitation and Restoration.

The research efforts, funded by the U.S. Department of Interior, initially focused on whether or not the high-flow experiments could rebuild and maintain sandbars in the stretch of river that flows through Grand Canyon National Park.

“With our first experiment, we gained more understanding of how the floods affect the physical environment,” Schmidt says. “With the subsequent experiments, we expanded our research to examine the effects of floods on the river’s biological resources, including native fishes, nonnative sports fishes, riverside vegetation and the aquatic food web.”

The dam has transformed the river whose floods once carried “tremendous” suspended sediment loads, he says.

“Today’s river has much colder water with very small sediment loads,” Schmidt says. “Sandbar beaches have eroded and riparian vegetation has invaded the river corridor to low elevation.”

Downstream from the dam, the Colorado has become less hospitable to native endemic fish, including the federally endangered humpback chub. Three other native fish have disappeared from the river.

Each artificial flood temporarily increased the size and number of sandbars downstream, but the scientists say it’s unlikely the sandbars will remain under normal dam operations. And while the inundations seemed to help native fish, they also encouraged nonnative rainbow trout, which may outcompete native species in some areas of the river.

The scientists also note that the experiments were conducted during prolonged drought conditions in the West. Future experiments could have decidedly different results during wetter years.

The report recommends continued high-flow experiments to rebuild sandbars.

“To restore a river, you have to have water,” Schmidt says. “But we’ll never be able to replicate the sediment conditions and stages that occurred before Glen Canyon Dam.”

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