For David Wegner to remember the time when one of the nation’s largest dams almost failed, all he has to do is look at the footlong chunk of concrete sitting on his desk.
In the spring of 1983, the Colorado River rushed into Lake Powell and almost overtopped Glen Canyon Dam. Crews opened Glen Canyon to full-throttle, sending as much water as possible through its eight hydropower turbines, four small outlet pipes and two spillways — tunnels that are designed to catch floodwater and channel it around the dam wall.
At the time, Wegner, part of a federal research team, was in a motorized boat about a half mile downstream of the dam. He could feel the mist from the water as it shot out of the base of the dam and hit the river below. The rushing water sounded like a freight train. As the boat’s engine fought chaotic white-capped waves, Wegner held on for dear life.
“You knew there was a great power upstream,” said Wegner, who at the time was researching the downstream impacts of the dam in the Grand Canyon for the federal government. “I had been up many times from Lees Ferry upstream — you’d never felt that sort of power.”
But there was a tiny threat within the gushing water with the power to rip the dam apart: bubbles of water vapor imploding with bursts of heat as hot as the sun and shockwaves strong enough to shatter concrete. Weeks after his turbulent boat ride, Wegner stood on top of the dam while floodwater still rushed out of its spillways. He felt vibrations under his feet. He looked down, saw the water turn the dusty red of sandstone, and knew something was very, very wrong.
“We’re all scared,” he recalled four decades later, “and we don’t know what’s going to happen.”
Today, the same forces that threatened the dam at high water are once again a threat as the dam’s reservoir, Lake Powell, shrinks to historic lows.
At low water levels, more air from the reservoir’s surface can be mixed into the water, ideal conditions for bubbles to implode with destructive force as the water travels through tubes and turbines. And this year, the reservoir’s water level is extremely low. Federal reports show that the dam might have to stop hydropower generation before the end of the year to avoid catastrophic damage caused, in part, by the small-but-mighty bubbles.
The Bureau of Reclamation has spent millions of dollars adding protective layers to some of the dam’s water release valves. State and federal officials are debating how to manage around the dam’s limitations as part of high-stakes negotiations this year.
But after a record-poor winter snowpack, the bureau is searching for more answers to an increasingly concerning question: How do they keep the water level high enough to avoid severe damage in the middle of a brutal drought — while meeting obligations to send water downstream for millions of people, cities like Phoenix, Las Vegas and Los Angeles and the farmers who grow the nation’s food?
They’ve already sent down emergency releases of water and cut back on deliveries downstream to keep more water in Lake Powell. Upstream states are cutting off water to farmers, per their water-sharing laws. One of the cheapest solutions could be paying those farmers, like many on Colorado’s Western Slope, to conserve water voluntarily in the future, some experts say. (They’ve tried that with mixed success.)
A more expensive option: Modify the dam itself.
Band-Aid solutions come with impacts — less water for downstream cities, less cheap, reliable hydropower for Western communities — and they still might not be enough to avoid a deeper crisis at the dam, experts say.
Maybe now is the time for new ideas, Wegner, a water and climate scientist, said. He went on to co-found the Glen Canyon Institute, a nonprofit dedicated to restoring Glen Canyon, after working with the Department of the Interior, which houses the Bureau of Reclamation, for over 20 years.
“Crises are a great opportunity for change,” he said. “We typically as a society don’t change unless we are faced with a crisis.”
The closest Glen Canyon Dam ever came to failing
The Bureau of Reclamation finished constructing Glen Canyon Dam in the 1960s as part of a multi-dam project that has stored water for the 40 million people living in the Colorado River Basin for decades. (Blue Mesa Dam, the largest dam in Colorado, is part of this federal project.)
It’s one of the largest dams in the nation, second only to Hoover Dam on the Arizona-Nevada border. Together, Glen Canyon Dam’s reservoir, Lake Powell, plus Hoover Dam’s reservoir, Lake Mead, comprise about 92% of the storage capacity for the entire river basin, which spans much of the Southwest including western Colorado.
Since its construction, the hydropower turbines at Glen Canyon Dam have helped generate cheap, reliable and renewable energy for communities across the West. It took 17 years to fill the majestic Glen Canyon with water to form Lake Powell. Now, people flock to its shores to camp and its marinas to jet around on motorboats.
In the last decade, the lake has become increasingly famous for the white mineral deposits on the red canyon walls, a bathtub ring caused by sinking water, prolonged drought and unyielding water demands.
In 1983, the near failure at Glen Canyon Dam had nothing to do with low water and everything to do with an onslaught of late season snow.
That year, a slightly above-average snowpack had gathered in the Rocky Mountains of Colorado and other upstream states. And the Bureau of Reclamation staff planned normal dam operations: Its modus operandi was to keep the basin’s reservoirs as full as possible to maximize their water savings accounts.
Then in May, spring snowstorms hit the high country.
Summer heat returned soon after, blasting the snow and causing runoff to surge downstream.
The previous fall had been wet, and soils couldn’t absorb any more water. Streams peaked. In Salt Lake City, city managers made sand bag barricades that channeled water into main streets that quickly turned into manmade rivers, according to the documentary film “Challenge at Glen Canyon” produced by the Bureau of Reclamation.
Upstream reservoirs were too full to take in the unexpectedly high surge of runoff. In western Colorado, Blue Mesa Dam sent heavy releases downstream to Morrow Point Lake and Crystal Reservoir — each releasing water in dramatic freefalls.
Every stream and river poured into Lake Powell. The flow into the nearly full reservoir quadrupled to 92,400 cubic feet per second on June 1, 1983, from 19,900 cfs on April 1, according to Bureau of Reclamation records.
Glen Canyon Dam, however, could only release so much water at once. The bureau teams opened the eight turbines to full throttle. Typically, those can only safely release up to 33,200 cfs, according to the Bureau of Reclamation.
They turned to the four river outlet works, 96-inch-diameter steel tubes that bypass the turbines and release water into the river at the base of the dam. At most, Reclamation can release a combined 15,000 cfs through the tubes.
But the water kept rising. The bureau turned to the dam’s spillways, which look like huge, open-mouthed tunnels that shoot into the rock on either side of the dam wall. These chutes around the dam are not designed for continuous use — they’re a flood control option meant to catch extra water when the lake gets too high. But they can release up to 276,000 cfs.
The bureau’s engineers knew the tunnels would take some damage, according to the Bureau of Reclamation’s documentary.
They opened them anyway. Water plummeted down into the pitch-black tunnel at 100 mph. It hit the tunnel’s elbow at the bottom of the dam, where the concrete chute flattens out and releases the arcing water into the river.
Still, the lake kept rising. Crews added plywood boards to the top of the spillway gates to create more storage space in the lake and relieve some of the burden on the immense tunnels.
They swapped plywood out for 20 tons of steel, not knowing if the machines that opened the spillway gates would be able to lift the extra weight, Wegner said. If they couldn’t, the rising water levels would go over the top of the dam and run down its front onto the hydropower station.
So the bureau kept using the spillways. It didn’t have any other choice.
A brief break for science
Deep inside the pitch-black tunnel, tiny bubbles started imploding.
As the high-velocity flows hit small bumps on the otherwise smooth concrete walls, the water deflected upward, creating a partial vacuum and producing millions of tiny vapor cavities.
When those bubbles collapsed, they sent out a shockwave that traveled as fast as 3,355 mph. The collapse caused a burst of heat over 10,000 degrees Fahrenheit, as hot as the surface of the sun. The force of the implosion threw over 10,000 psi of pressure at the spillway’s concrete walls. The normal pressure of a kitchen faucet is between 40 and 80 psi.
“Just think of a million bubbles exploding and the ripple effects that can have,” Wegner said. “It’s physical waves of energy that are attacking the concrete.”
Micro-breaks formed in the concrete. Then small pits. Once one hole appeared, a leapfrog action formed another and another down the tunnel like stairsteps.
It’s a process called cavitation, and in 1983, it caused the biggest failure in the dam’s history.
Something’s wrong with the spillways
By mid-June 1983, Wegner, and everyone at Glen Canyon Dam, looked over the side of the dam to the water roaring into the river far below. They felt vibration under their feet. They saw the roaring arch of water leaving the spillway sputter and choke.
The next day, the tunnel vomited its innards, spitting out chunks of concrete in red, sandstone-colored water like something out of a horror movie.
“You knew that (the water) had compromised the spillway concrete and rebar lining and was now into the sandstone,” Wegner said. “As I say that, I’m looking at a chunk of the spillway here on my desk that reminds me every single day of the power of physics.”
The bureau’s staff had no idea how bad the damage was. They didn’t know if the cavitation was digging further into the sandstone or toward the dam itself.
Eventually, they could slow the flow through the spillways to inspect them. Experts paddled a raft into the bottom of the tunnel and dropped down its steep throat from above using a cart tied to a cable.
Final inspections revealed broken steel bars. Ripped-apart concrete lining. They found holes 20 feet wide and up to 4 feet deep. A gigantic pit 32 feet deep, 40 feet wide and 150 feet long. It would eventually take about 2,500 cubic yards of concrete to fill it — enough to fill an Olympic-size swimming pool.
The dam wall wasn’t going to rip apart and let Lake Powell flow into the Grand Canyon, Wegner said. But its spillways failed. And the hydropower plant could have been lost, too.
“You got to give them credit. They did a lot to minimize potential disaster,” Wegner said. “But, all that being said with what we know today, would it have been more appropriate to release all the water you could earlier in the year to make space behind Glen Canyon Dam?”
Today’s battle against the super bubbles
Glen Canyon Dam’s problem in 1983 was too much water — the lake’s elevation eventually rose to 3,707 feet above sea level. (Its official capacity is 3,700 feet.)
Now, the dam has the opposite problem: Too little water and the host of issues that comes with it.
Glen Canyon Dam’s main job is to store water and release it through the Grand Canyon to Hoover Dam, which then releases it to millions of people. After 25 years of drought, the spillways aren’t even part of the conversation. The lake’s water level is too low. Dam managers must depend on two main release options: the turbines and the small, steel river outlet tubes.
There’s a big concern with low water and turbine releases: As reservoir levels drop, whirlpools could start on the lake’s surface, more air can get sucked into the flow of water, and vibration and surges of high water pressure can occur, according to the bureau.
So can cavitation. And if tiny bubbles start collapsing with explosive force within turbines, that’s a problem. The turbines are finely tuned with spinning propellers inside. If they wobble by even a small amount, it could knock the turbine out of balance, causing speeding propellers to rip through turbine walls and wreak catastrophic havoc on hydroelectric facilities.
“They’re in the basement of the dam. Because of everything that’s connected to them, you would likely see large-scale destruction in the power plant itself,” Wegner said. “It’s not good to have cavitation in turbines. It’s not good to have cavitation in spillways, and it’s not good to have cavitation in pipes.”
The bureau has said for years that it wanted to keep a cushion of water in Lake Powell to avoid these problems. That meant keeping the lake above 3,525 feet in elevation. As of May, the lake’s elevation was 3,527 feet. By December, it could easily fall to 3,510 feet, according to the bureau’s projections.
If next winter also results in a poor snowpack, Lake Powell could fall so low that the bureau can not send water through the dam’s turbines at all. Instead, they will be forced to channel the entire Colorado River around the turbines and through the four, 96-inch river outlet tubes for months or longer.
The tubes were not designed for sustained, high-velocity flows, especially at low lake levels. In 2023, Reclamation reported minor cavitation damage to the aging coal-tar coating after a high-flow experiment meant to benefit native fish populations and environments downstream.
The bureau spent $8.9 million on a new protective coating to the tubes, saying it was part of routine upkeep, not specifically cavitation protection. This new lining had already been successfully applied to numerous dams, including Fontana Dam in North Carolina, Pineview Dam in Utah and Grand Coulee Dam in Washington, according to the bureau.
Reclamation also limited how much water can flow through the tubes over a long period of time when the reservoir is low, Katrina Grantz, Upper Colorado deputy regional director for the Bureau of Reclamation, told water experts gathered at the University of Colorado in Boulder in early June.
“Glen Canyon Dam can be safely operated within these limitations,” Grantz said.
Cavitation, however, is still a concern. So is the risk that stirred-up sediment could scour or clog the dam’s plumbing, she said.
Searching for new solutions
The bureau does not have experience managing Glen Canyon Dam at low water levels. Now they’re caught between a rock and a hard place: They have to make sure water reaches downstream communities — and they can’t risk expensive damage or safety issues at the dam.
So they’re trying out other tools.
This year, state, federal and tribal officials must create new rules for how to manage Glen Canyon Dam, and other key dams, going forward. The bureau has already released different management options, each based in part on preventing damage at the dams — especially from cavitation.
Those high-stakes negotiations have been deadlocked for years over potential painful water cuts during the basin’s driest years. The new rules must be in place by October.
In the meantime, the bureau is avoiding the dangerous tiny bubbles by cutting releases and sending emergency water from upstream dams. Both will help avoid extremely low water levels in Lake Powell.
It’s a temporary solution, experts say. These emergency releases shrink upstream reservoirs and can hurt marinas, boat rentals and businesses around the reservoirs. Plus, once released, the jig is up. The bureau can’t tap those reservoirs next year unless this winter comes with enough snow to replenish them.
So, the bureau has also cut its downstream releases to a historic low: 6 million acre-feet, the lowest release allowed under the current regulations. (One acre-foot roughly equals the annual water use of two to three households.
But the low release downstream brings the basin’s seven states closer to a legal tripwire that could trigger lawsuits and possibly force water cuts in upstream states, like Colorado, experts say.
Some say paying the basin’s largest water users, mostly farmers and ranchers, to use less water is the most affordable way to refill Lake Powell.
Colorado and other upstream states have tried this, and the water savings were minimal, just 1% of the states’ annual use. The political debate is fiery. Upstream farmers don’t want to shrink their businesses to help Lake Powell or Glen Canyon Dam because their conserved water would just be used by people downstream. In Washington, a bill to refund the program has been stalled for months.
Others are pushing for more permanent solutions, like replacing the aging turbines with new models that can operate better when the lake’s level is low. Or building new tunnels that can move water around the dam when the lake is extremely low. These tunnels would avoid damage at the dam while still allowing water to reach communities across Arizona, California, Nevada and two states in Mexico.
“This whole system is now being hamstrung by this infrastructure problem at Glen Canyon Dam,” Eric Balken, executive director of the Glen Canyon Institute said. “We’ve been saying that for many years, and now the Lower Basin states are saying the same thing.”
The Bureau of Reclamation started studying this and other low-water management options at Glen Canyon Dam in 2023. Its report should be ready in 2027, the bureau said.
“As an engineer, I can tell you, we can redesign the dam, but it’s going to cost you money. It’s going to take some time,” Wegner said.
He recalled a day in 1984 when he was once again at the bottom of the dam. The water had calmed. The spillway was being repaired as a historically large snowpack once again built up in the mountains.
Wegner looked down into the Colorado River and saw a footlong chunk of concrete. He’s kept it ever since to serve as a tangible reminder of what can happen when things go wrong.