1. The Failure of Teton Damby
Anthony Gilbert
Reza Ghany
Charlie Pearcy

2. Contents Introduction Dam construction Geology of the site
Failure of the dam
Aftermath of the failure
Geology behind the failure
Engineering factors behind the failure
The future of the Teton Dam site
Conclusion

3. Introduction
Earth dam located between Fremont and Madison Counties on the Teton River, Idaho, USA
Dam dimensions – 940m long 93m high and 540m wide at the base
Construction began in June 1972 and was completed in November 1975
Construction cost $49,000,000
Intended to create the Teton reservoir with a capacity of 228,954,000m3

4. Dam Construction
Zone 1- Impervious centre core with clayey silts of aeolin origin
Zone 2- higher compaction, filter layer that controls seepage through core and rock foundation.
Zone 3- structural stability
Zone 4- Random cofferdam fills (allowing construction of dam in dry)
Zone 5- Rock-fill to protect outer embankment slopes
Note: Only one grout curtain installed, higher than anticipated
grout take (due to poor rock condition)

5. Geology of the Site Dam site Snake River Plain
Steep walled canyon on a broad tectonic depression
The volcanic rock at the dam site
Hard, welded, rhyolitic ash-flow tuff (compacted ash)
Permeable, one side highly fissured, unstable
Sedimentary rock below
Bed Rock
Open-jointed rhyolite Basalt

6. Failure
On Thursday 3rd June 1976 water was observed seeping through the dam, it was inspected by engineers who dismissed that there was a problem.
At 7.30am on Saturday 5th June 1976 a muddy leak appeared suggesting sediment was in the water seeping through the dam. Again, engineers dismissed suggestions of a problem
Teams of workmen using mechanical equipment attempted to stem the flow through the dam ultimately unsuccessfully with 2 workmen having to be rescued when their bulldozers were swallowed up by the collapsing dam
At 11.15am an order to evacuate downstream was given
The dam was completely breached at 11.55am releasing 57000m3/s of water
By 8pm the dam was empty

7. Failure
Approx 11.20am
Approx 11.40am
Approx 11.50am

8. Failure
Approx 12pm
After 12pm

9. Aftermath
Upon failure the water rushed down the Teton canyon destroying the entire ecosystem.
Communities of Wilford, Sugar City, Hibbard & Rexburg were badly hit by flood water.
Photograph taken in Rexburg
11 people died in resulting floods
Danger of collapse of ‘America Falls Dam’, however increasing flow through the dams slipways ensured its integrity
Estimated cost of damage & cleanup up to $2billion

10. Geology Behind the Failure
Volcanic fumaroles
large voids
Favored development of cracks
Fill material – rhyolite, basalt
Not suitable for foundations
Permeable, one side highly fissured, unstable
trenching abutment rock providing large core-rock contact and long flow path (for low seepage gradient)
Arching (increase in stress in some areas and a reduction in others)

11. Engineering Factors Behind Failure
Following the failure, an investigative panel was selected to
review the cause. The panel issued its report in December 1976.
The report concluded that the main contributing factors to the dam failure were:
Erosion/Piping
The geology of the site
The design of the dam
The lack of instrumentation to warn of changing conditions

12. The Future of The Teton Site
In July 2009, there was new speculation about rebuilding in order to provide water for irrigation.
The Bureau of Reclamation has reportedly set aside $400,000 of the $800,000 needed to study the feasibility of rebuilding.

13. Conclusion
Collapse caused by a combination of bad engineering decisions related to the geology of the site.
Warning signs ignored early on the day of collapse. Evacuation order could have come sooner perhaps saving more lives
“As every dam engineer knows, water also has one job, and that is to get past anything in its way!!”