Controlled flooding moves Canyon sand
Exercise shakes up silt in shadow of N. Arizona dam
PAGE — Octavia Patno and her mom, a federal hydraulic engineer, stood on a narrow walkway at the base of Glen Canyon Dam Monday morning, their heads covered with hard hats. The Colorado River flowed below. Red-rock canyon walls towered above. The dam’s hydropower turbines hummed.
At 11 a.m., it was time for Octavia, 13, to flood the Grand Canyon. She pulled a lever
above four empty jet tubes that pointed toward the river. It was heavier than she expected. In the next moment, she turned around, her mouth open in surprise.
The first jet tube had opened and water gushed into the morning air, cascading into the river below. Three other tubes opened in succession like giant faucets. Below, the water crashed against the canyon walls.
This was how the U.S. Bureau of Reclamation began a four-day controlled flood of the Grand Canyon. The goal is to help move sand and sediment down the Colorado River the way the river’s natural flows did before construction of Glen Canyon Dam.
Beaches and sandbars along the river have eroded since the dam blocked the Glen Canyon in 1963; many have disappeared into the clear waters of the Colorado River that ebb and flow with power demands. The loss of beaches and backwater sandbars leaves less habitat for native wildlife species in the Canyon.
This floods will last about four days, with river flows peaking at 38,100 cubic feet per second. The flow from the dam typically varies between about 8,000 and 25,000 cubic feet per second.
Creating the artificial floods won’t result in the loss of water, officials said. The bureau will adjust scheduled flows from the dam to account for the high flows. Water from Glen Canyon Dam flows into Lake Mead, which supplies water to millions of people in Arizona, Nevada, California and Mexico.
This is the eighth time since 1996 that officials have conducted the controlled floods. The first flowed for more than seven days, peaking at 45,000 cubic feet per second.
The National Park Service is advising people who plan to be on the river or in the canyon this week to be aware of the higher flows on the river.
Transporting sediment and sand down river used to be nature’s job. The Colorado River was muddy with sediment before Glen Canyon Dam turned the water clear. But those floods were larger and less predictable than this week’s experimental flows.
“These floods are tiny,” said Jack Schmidt, a geomorphologist at Utah State University and the former chief scientist at the Grand Canyon Research and Monitoring Center in Flagstaff. He was one of the researchers who devised the high-flow experiments.
The controlled floods are about half the magnitude of pre-dam floods, he said. They flow for several days, while the natural floods could continue for one to two months.
And officials have triggered recent floods in November, he said, while snowmelt from the Rocky Mountains would raise water levels in May and June.
Other floods occurred in the fall, Schmidt said, “but not typically as late as November.”
The loss of bigger floods has also meant more vegetation on beaches and sandbars, said Michael Moran, a scientist at the Grand Canyon Research and Monitoring Center.
The controlled floods don’t do much about the vegetation, he said. And many of the largest sandbars aren’t around anymore.
“There’s just a lot more vegetation than there was in the past,” he said. “In the past, really big flows would happen sometimes … and they would take the vegetation out, scour it out. We don’t have those anymore so the vegetation gets a hold and really doesn’t really ever leave.”
The Paria River “occasionally and sporadically” delivers sand and sediment below the dam to Grand Canyon, Schmidt said.
So does the Little Colorado River, according to the Bureau of Reclamation.
But more than 90 percent of the sand and sediment that was once transported through Grand Canyon is now trapped in Lake Powell, Schmidt said.
This sediment is lost to the river, said Marlon Duke, a spokesman for the Bureau of Reclamation. The controlled floods do not give it back.
It could take 100 years for the sediment to even reach Glen Canyon Dam, he said. “Right now the sediment … is about 100 miles up reservoir.”
Water managers count on the artificial floods to move sediment downstream from the tributary rivers.
“These controlled floods are one way that we make the best out of a bad hand,” Schmidt said.
The sandbars and beaches that controlled floods rebuild can provide camping sites, create habitat for fish and wildlife, and protect plant communities and archeological sites, according to a federal environmental assessment.
“All in all … we’re seeing some positive downriver effects,” said Emily Davis, a spokeswoman for Grand Canyon National Park.
Some groups question whether the controlled floods are worth the cost. Others say they’re too little, too late.
“I would prefer to see (controlled floods) designed to not be as impacting on hydropower,” said Leslie James, director of the Colorado River Energy Distributors Association, whose members buy hydropower from Glen Canyon Dam.
During the controlled floods, some of the water generates power, but some of it bypasses the dam’s turbines, the Bureau of Reclamation said. The Western Area Power Administration, a branch of the U.S. Department of Energy, must buy additional power later on to make up for the power that wasn’t generated by the diverted water.
The controlled flood this week, which flows from Monday to Thursday, will cost the agency an estimated $920,000, the Bureau of Reclamation said.
Although the accomplishments of the controlled floods are impressive, they don’t get to the heart of the problem, said Eric Balken, director of the Glen Canyon Institute.
“In a way it is like putting a Band-Aid on a gaping wound,” he said. “It doesn’t actually get to the heart of the problem.”
Environmental coverage on azcentral.com and in the Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow the azcentral and Arizona Republic environmental-reporting team at OurGrandAZ on Facebook, Twitter and Instagram.