New measures could reduce Glen Canyon Dam’s impact on the Grand Canyon — a bit

As long as the dam remains in place, impacts are inevitable.

 

If the San Juan River were a freeway, Glen Canyon Dam would be a 50-car pile-up. It forces the river to back up and spread out for dozens of miles. As the river morphs into Lake Powell, the sand in its current settles out. A rock overhang at Grand Gulch where boaters once lounged is now buried more than 30 feet deep.

Before the dam killed the current, the San Juan carried all of this silt to the Colorado, which spit much of it through the Grand Canyon, replenishing hundreds of sandbars. These expansive blonde beaches, which form in eddies, are river runners’ favorite campsites, and they provide backwater habitat for fish. But today, about 95  percent of the sediment that once washed through the canyon sits at the bottom of Lake Powell, and the sandbars have shrunk: The Colorado erodes them, but doesn’t build them back up.

This is one of the problems the 1992 Grand Canyon Protection Act was supposed to correct. It directed federal officials to figure out how to manage the dam in a way that did less harm and even protected the national park’s assets. In addition to threatened sandbars, three of eight fish species native to the Grand Canyon have disappeared since the dam went up, and two are endangered.

But can altering dam operations really help the river when the dam itself imperils it? Scientists have explored this question since 1992, and their research informs the Bureau of Reclamation’s draft management plan for the dam’s next 20 years, released earlier this year. Conservationists are optimistic that it will yield improvements downstream, but only small ones. “You’re really just trying to make the best of a bad deal,” says Utah State University watershed sciences professor Jack Schmidt.

U.S. Geological Survey

A sandbar gained sediment after a controlled flood was released from Glen Canyon Dam in 2012.
U.S. Geological Survey

This is the second such plan for Glen Canyon Dam. The first, in 1996, allowed managers to unleash experimental floods to flush sediment from downstream tributaries — the 5 percent not stuck behind the dam — through the canyon. They hoped a rush of silty water would rebuild sandbars. But the floods were politically and logistically difficult, since they resulted in lost hydropower, and the Bureau had to complete complicated environmental assessments before each one. Years passed between floods in 1996, 2004 and 2008, limiting their efficacy. While they did boost sandbars, within six months or so, the beaches eroded again.

Then, in 2012, then-Interior Secretary Ken Salazar authorized floods to occur whenever conditions were right until 2020. Floodwater thundered through the canyon in 2012, 2013 and 2014. It’s unclear if frequent floods can make sandbars larger over time, says Paul Grams, a U.S. Geological Survey researcher, but monitoring suggests they can at least stop further decline.

The new plan goes further by making floods a permanent feature of dam management. “That’s a big deal,” says Ted Kennedy, a native fish biologist with the Grand Canyon Research and Monitoring Center. “Those high-flow experiments were really hard to get implemented.” 

The plan will also kick off new experiments to help fish like the endangered humpback chub. These fish evolved in turbid desert rivers that could reach 85 degrees in summer. Today’s Colorado is a different world: The dam releases water from Lake Powell’s cold depths, and near it, the river hovers around 46 degrees year-round. There’s no way to warm these areas without either draining the reservoir, or adding expensive infrastructure that lets the dam release water from warmer layers near the surface. Neither option is currently on the table.

But there might be other ways to help fish, Kennedy says. Chub spawn almost exclusively in the toasty Little Colorado, then move into nearby parts of the mainstem Colorado, where their growth is inhibited by chilly water. The water does warm as the river twists further from the dam, but though it should be good habitat, few chub live in these downstream reaches.

Scientists think that could be because there aren’t enough bugs to eat there. Aquatic insects lay their eggs at river’s edge, and when the water level drops, as it does daily when water releases fluctuate with hydropower demand, the stranded eggs shrivel and die.

The plan proposes to eliminate flow fluctuations on spring and summer weekends, when electricity demand isn’t quite as high, in hopes of keeping eggs wet and boosting insect numbers. More food might help chub populations colonize and prosper in the river’s lower reaches.

Eric Balken of the Glen Canyon Institute is glad that the Bureau is trying to improve the river’s health. “But it’s just a Band-Aid on a gaping wound,” he says. “What we’re not happy with is that they more or less ignored ideas that they considered outside-the-box thinking.” These include requiring Lake Mead to be filled before any water is stored in Lake Powell, which would reduce the water lost to seepage in the system, warm the river, and allow Glen Canyon to emerge from submersion by draining much if not all of Powell.

The plan, instead, represents “the art of the possible,” says David Nimkin, with the National Parks Conservation Association. He thinks it will yield positive, but marginal, gains. “You can do more harm than you can do benefit with the dam,” he says. “Glen Canyon Dam, for the time that it operates, has a profound impact. And that’s a fact.”

Contributing editor Cally Carswell writes from Santa Fe, New Mexico. 

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