The Teton Dam Disaster - An Engineer's Aspect


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Monday, September 20, 2010

The Teton Dam Disaster

Left to right: My cousin, LaRae, me and my sister, Jenny on June 5, 1976.

On June 5, 1976, The Teton Dam burst. I was a child living in the path of the oncoming water. Luckily, we lived near Idaho Falls. We had nearly two days to prepare to do battle with the raging flood.

On that beautiful Saturday, we had a party for my brother and cousin. My brother had recently turned eight and June 5 was my cousin's eighth birthday.

After hearing of the dam bursting, my father and all the adults leaped into action. There was much sandbagging and shoring up of the Snake River banks to be done in order to keep the flood from destroying our homes.

My mother, Judy South, my father, David South, with my sister, Jessica and my brother Dave on June 5, 1976.

My father and uncle both had pilot's licenses and they flew over the devastated areas a few days later. They brought back woeful news and slides.

My sisters, Melinda and Rebecca on June 5, 1976.

After the floodwaters had receded, they drove north and took many photos of the destruction.

I used the photos they took during that trip to make a video about the Teton Flood and posted it on YouTube. These are pictures of the flood that have never been seen.

Sources used in video: Teton Dam Failure Narrative and Teton Dam Flood.

Water pouring out of the reservoir of the Teton Dam in Idaho following its catastrophic failure on June 5, 1976. Source: Wikipedia Commons.

"The Teton Dam was a federally built earthen dam on the Teton River in southeastern Idaho, USA which when filling for the first time suffered a catastrophic failure on June 5, 1976. The collapse of the dam resulted in the deaths of 11 people and 13,000 head of cattle. The dam cost about USD $100 million to build, and the federal government paid over $300 million in claims related to the dam failure. Total damage estimates have ranged up to $2 billion. The dam was never rebuilt." According to Wikipedia.

The "Teton Dam Failure Case Study" was presented at the 3rd ASCE Forensics Congress. They concluded that, "the failure of the Teton Dam could have been avoided. Early investigations into the geology of the site showed that the rocks in the area were almost completely of volcanic origin. These volcanic rocks consisted of basalt and rhyolite. In the footnotes to the geological survey of January 1971, the rhyolite is defined as “lightly to locally highly fractured and jointed, relatively light weight” (pp. 4-7, Independent Panel, 1976). This was also the condition for other possible sites located upstream of the site where the dam was constructed. These materials are usually avoided due to a history of erosion and deposition. The reason for the extensive foundation was the poor quality of the underlying material, including the grout curtain. The grout curtain failed to do its job of preventing these materials from being easily washed away.

The panel noted that the design did not provide for downstream defense against cracking or leakage, and did not ensure sealing of the upper part of the rock under the grout cap. The grout curtain was not constructed in three rows, and the reliance on a single curtain was judged to be “unduly optimistic.” The dam and foundation were not instrumented sufficiently to warn of changing conditions."

The case may be best summarized in the words of the panel report – “the Panel concludes (1) that the dam failed by internal erosion (piping) of the core of the dam deep in the right foundation key trench, with the eroded soil particles finding exits through the channels in and along the interface of the dam with the highly pervious abutment rock and talus, to point at the right groin of the dam, (2) that the exit avenues were destroyed and removed by the outrush of reservoir water, (3) that openings existed through inadequately sealed rock joints, and may have developed through cracks in the core zone of the key trench, (4) that, once started, piping progressed rapidly through the main body of the dam and quickly led to complete failure, (5) that the design of the dam did not adequately take into account the foundation conditions and the characteristics of the soil used for filling the key trench, and (6) that construction activities conformed to the actual design in all significant aspects except scheduling.” (pp. iii-iv, Independent Panel, 1976).

In the design and construction of earth dams, it is necessary to select proper materials that are sufficiently resistant to piping and to ensure that they are compacted to the proper density. If a grout curtain is used, methods must be available to ensure that it is continuous and forms a seal with the underlying rock. The design should incorporated adequate defense against cracking and leakage. Finally, dams must have sufficient instrumentation to provide early warning of piping and impending failure.

As a final comment, this case stands as a warning against overconfidence and hubris. “As every dam engineer knows, water also has one job, and that is to get past anything in its way” (p. 93, Macauley, 2000).