Teton Dam Failure - 50 Years On
The Teton Dam failed 50 years ago — a terrible story for the residents of eastern Idaho. Below is the story of how the dam came to be and the tragic events of June 5th, 1976. As somber as this memorial is, this is also an opportunity to speak out against ill-conceived dam projects. Ideas about rebuilding the Teton Dam are gathering steam, and Idaho Rivers United is firmly opposed to any plan to erect a dam in a place that has already proven itself to be unsuitable for water storage.
###
Teton Dam, June 5th, 1976, just before the full breach of the reservoir. ID-L-0008, WaterArchives.org
“Look, there goes the whole side! There goes the whole complete side of the north edge of the Teton Dam! And the water is monumental! Holy! People downstream better get out!” Don Ellis, KRXK Radio, June 5th, 1976
At 7:30 am, it was a wet, muddy spot on the downstream side of a brand-new earthen dam. By noon, it had briefly become one of the most powerful rivers in the world. Before it completed its first fill, the $100 million Teton Dam suffered a catastrophic failure over the course of a single morning with grim consequences: 11 people dead, close to 20,000 livestock killed, 100,000 acres of farmland ruined, and a disaster area of 3 towns that now looked like a warzone.
What were the primary reasons that led to this tragedy? Greed, hubris, and an unwillingness to listen to science. What is even more unnerving? The increasing pressure to rebuild the Teton Dam and try again.
The Political Powers Behind the Dam
Dams were all the rage of the engineering world in the mid-twentieth century. The “Big Dam Era” saw the construction of more than 40,000 dams between 1950 and 1979, many of them by the Bureau of Reclamation (BOR). The American West was being ‘tamed;’ even rivers were now being curbed to the will of man. In eastern Idaho, local politicians saw the Teton River as a resource that could be turned into a watery bank account. Not only could flood control be installed, but area farmers could now depend on a reliable irrigation source, a key worry of the 1960s amid a widespread drought affecting the region.
Idaho’s delegation was instrumental in moving the project forward in the ‘50s and ‘60s. Senators Henry Dworshak and Herman Welker each brought power and a narrative to solidify the future of the dam. Dworshak sat on the Senate Appropriations Committee and convinced a coalition of his colleagues that the Teton Dam wasn't just a local project, but a "national investment" that would pay for itself through increased crop yields and tax revenue. Welker framed the Teton Dam as a matter of national security; instead of just ‘wasting’ water by allowing it to flow to the ocean, it must instead be used to secure agricultural independence, a means of self-sufficiency in a world of global uncertainty.
Congressman Orval Hansen of Idaho’s 2nd district became a staunch defender of the Teton Dam in the early ‘70s as the environmental movement gained traction. With the advent of the National Environmental Policy Act (NEPA), opposition groups now had a tool to sue the BOR. Hansen argued that too much had been invested in the project to be stopped by new environmental policies. He tirelessly advocated for the project in annual funding bills; in total, the dam received $100 million in appropriations.
But sheer political willpower was not enough for the Teton Dam to endure.
What Lies Beneath: Swiss Cheese Geology
The BOR was ready to award a construction contract for the dam in early 1971, but a memo from David Schleicher of the US Geological Survey (USGS) raised alarms about the project. While many dams around the country had been placed in suitable spots for large reservoirs, by the end of the Big Dam Era, sites were being scouted that could at best be classified as “marginal.” The Schleicher Memo warned of two major factors that make the Teton Canyon a very risky bet for storing water. The canyon was formed by rhyolitic ash-flow tuff – essentially volcanic ash that has been welded together. The cooling of this ash resulted in widespread ‘joints,’ or large vertical cracks. Schleicher argued that these voids would allow water in a reservoir to escape around and under the dam, no matter how much cement the construction engineers used to fill in the holes.
Apart from this “swiss cheese” bedrock, another underlying factor was the seismic activity of the region. This area is littered with faultlines, including the Teton Fault, largely caused by the movement of the Earth’s crust over the geologic hotspot that is now located underneath Yellowstone National Park. The crust has been stretching here for millions of years, helping to create voids and weaknesses in the ground underneath eastern Idaho. Not only that, earthquakes are not uncommon in the area. The largest tremor before the dam was built was a magnitude 7.3 at Lake Hebgen, Montana, 60 miles away. This major earthquake created Quake Lake and killed 28 people in 1959, only 11 years prior.
Why didn’t the state and the country revolt against the project after the publication of the Schleicher Memo? Because it was buried before it ever saw the light of day. This ‘internal’ memo wasn’t widely known outside the BOR and the USGS. The BOR called it alarmist, and its existence was suppressed from even some members of Congress during the final rounds of funding. It was treated as an internal dispute, rather than a life-threatening warning. Only after the collapse of the dam and the resulting investigation did the Schleicher Memo come to light.
The Dam
The BOR awarded the construction contract jointly to the Boise firm Morrison-Knudsen and Peter Kiewit Sons’ at the end of 1971. Plans moved forward with drilling holes and injecting over 500,000 cubic feet of cement grout into the ground and the canyon walls; this strategy to strengthen the bedrock and fill in the swiss cheese geology was referred to as the “Grout Curtain.” The BOR was confident that the grout curtain would be sufficient, but engineers failed to achieve a watertight seal, even after doubling the amount of cement originally planned.
By 1973, the bulk of the visible structure, the earthen-fill dam, was being constructed. Millions of cubic yards of fine-grained silt called loess was used as the heart of the dam, intended to be the waterproof barrier holding back the river. Surrounding that, sand, gravel, and larger rock-fill zones provided weight and structural stability. The embankment was finished in October 1975, towering 305 feet above the riverbed and stretching 3,100 feet. Earthen-fill dams are extremely thick at the bottom in order to support their own weight; the Teton Dam measured 1,700 feet wide at its base.
The dark streak along the left side of the dam is the beginnings of the leak, early morning June 5th, 1976. ID-L-0002, WaterArchives.org
Disaster
During its first filling in October 1975, the water level rose by one foot per day. The BOR wanted to utilize the irrigation water for the 1976 season, so the level doubled to 2 feet per day at the end of March. With a massive spring snowmelt looming, the rate was again raised to 3-4 feet per day by mid-May. The dam’s integrity went untested; the typical practice is to fill to a certain level and then pause, to monitor for leaks and to allow the dam to settle. This did not happen at Teton.
The silty loess of the earthen core, while highly compacted and good at blocking water when confined, has very little cohesion if water moves past it with any real velocity. With the rapid filling of the reservoir, the silt was exposed to being stirred up and dissolved like a sugary solution, eating away at what should have been acting like a dense barrier. The quickly rising reservoir placed great hydraulic pressure on the core and the surrounding rock abutments. Water eventually found its way to unsealed rock fissures on the downstream face of the dam.
On June 5th, 1976, the reservoir was only 3 feet below reaching the spillway. Roughly 80 billion gallons of water waited inside the Teton Canyon for only a few hours more. At 7 am, the morning crew noticed two small seeps on the north (righthand) side of the canyon wall where it met the dam. This, in and of itself, is not uncommon, as new dams often have seeps. However, by 8:30, a third and larger leak was spotted. The water leaking out was not clear; it was muddy – a sign that the dam’s internal silt core was being tunneled and carried away.
Soon a boil of water and mud began erupting from the dam itself. BOR sent in two bulldozers to try to fill the hole with rocks and fill. A sinkhole opened up on the crest of the dam, and the dozer operators realized the personal danger they faced. They climbed away from their equipment to safety just before the ground opened up and swallowed their machines.
By 10:30, witnesses described seeing a fire hose of water shoot out of the face of the dam several feet wide. A whirlpool appeared in the reservoir just above, indicating that the erosional tunneling had made it completely through the dam. The crest of the dam sagged as the structure underneath washed away.
This “V” notch deepened until it gave way, and water began to stream over the top. Within moments the trickle became a torrent, and the flood began scouring the earth-fill core, easily cutting vertically through the dam. At 11:57 am, the main wall crumbled, and a debris flow more than 20 feet high came crashing down the canyon. A sound witnesses compared to a jet engine roared through the canyon as the dam collapsed.
Teton Dam, June 5th, 1976, the reservoir emptying. ID-L-0010, WaterArchives.org
The first place to bear the brunt of this biblical flood was Wilford. Roughly 20 minutes after the debris flow launched from the dam, the town was obliterated. Buildings were simply wiped away from the land. Sugar City was next; 250 of the 300 homes there were destroyed or damaged beyond repair. The town was buried under what became known as “Teton Mud.” Rexburg, the largest town around, saw floodwaters 6 to 8 feet deep. Thousands of residents fled to Ricks College (now BYU-Idaho) atop a hill, the only safe location they could reach, where they watched the town flood below.
Other towns to suffer major impacts and flooding from the disaster include Hibbard, Firth, Roberts, Idaho Falls, and Blackfoot.
Wilford. ID-L-0013, WaterArchives.org
After the Flood
Miraculously, only 11 people died in this tragedy. It was daytime, and warnings were sent out starting an hour before the dam collapsed. Estimates of the livestock lost range from 13,000 to 20,000. The topsoil of this heavily agricultural region was washed away, replaced by Teton Mud, which turned into essentially concrete when it dried. Damages were estimated at roughly $400 million; $322 million in claims were ultimately paid out to 15,000 residents – about $1.8 billion today.
The ruins of the remaining dam still stand at the site, stabilized by the BOR. They serve as a ghastly reminder of the mistakes of the past. One silver lining of this disaster was the implementation of new dam policies and standards. President Jimmy Carter’s Federal Guidelines for Dam Safety instituted independent review of designs and safety inspections, risk-based analysis for the consequences of failure, and emergency action plans in the event of imminent failure. A National Dam Safety Program inventories the age and hazard potential of 90,000 US dams, grants state assistance to help states hire inspectors to monitor non-federal, privately owned dams, and trains dam personnel to recognize the early signs of piping and seepage. The Teton Dam site is now used as a training ground for dam safety officials, and this event is one of the most heavily studied engineering disasters in the country, if not the world.
Rexburg. ID-L-0043, WaterArchives.org
Today, despite this tragic lesson, the possibility looms that the Teton Dam will be resurrected. As Idaho sees growing strain on our water resources, some are returning to the Teton Dam as a potential solution. While these efforts are still in the early stages, it is alarming to witness. All of the underlying engineering factors that ultimately helped compromise the integrity of the dam continue to exist and will always linger along the banks of the now-empty reservoir.
As we continue to grapple with drought and low-snow years, there are legitimate questions and concerns about how to best secure and store crucial water resources. There are other options for increasing storage in the upper Snake basin, including increasing capacity at other, existing reservoirs. And the realities of water demand and decreasing snowpack mean that even if Teton was still standing, there wouldn’t be enough water available in the basin to fill the reservoir most years.
All of this is complicated by the the Eastern Snake Plain Aquifer. This underground storage vault covers more than 10,000 square miles of Eastern Idaho with the capacity to store an estimated 200-300 million acre-feet of water, roughly the equivalent of Lake Erie.
Since the 1950s, the aquifer has been declining. Due to increased efficiency in irrigation practices, urban growth, and increased demand, we have continually outpaced the recharge of this incredible resource. Despite this fact, there is increasing attention and effort to balance the demands placed on the aquifer and increase the rate of recharge. With all things water in the West, the idea of recharge is easier said than done. This effort is a classic story of western water tension, placing increasing agricultural and municipal dependencies against a finite resource.
Regardless of this tension and complex path forward, IRU staunchly opposes the idea of rebuilding this disastrous dam. We genuinely hope that clearer heads prevail and these efforts to rebuild the dam quietly disappear; we will continue to monitor the situation and be ready to do everything we can to oppose repeating the mistakes of the past.
