Group 22:
Brian Cleere,
Kevin O'Connell,
Michael Enright.
26/10/2007
THE TETON DAM FAILURE, IDAHO, USA
IINTRODUCTION:
The Teton Dam Collapse occurred on June 5th 1976 on the Snake River Plain in south-east Idaho,
USA. The Dam was commissioned by the US Government and came to a grand total of $100
million to construct. Its failure caused the death of 11 people and a further 13000 cattle were
destroyed. The US Government paid out another $300 million worth of claims and the total damage
costs of this catastrophe have reached as high as $2 billion.
The dam was built on the Teton River, in the Teton canyon in Madison County. The dam was an
earth fill dam standing 93m in height and spanned 975.5m. It was originally designed for numerous
reasons including: flood control, irrigation, production of hydro-electricity and water based
recreation.
In this report, we will discuss the causes of the failure with reference to site selection, construction
techniques, and rock composition and how this disaster could have been prevented.
SITE HISTORY:
The design of the project was undertaken by the U.S Bureau of Reclamation. The first site
investigations began as early as 1932. Numerous sites had to be studied and examined to determine
whether they had adequate geological conditions for such a structure. Between 1932 and 1961
sixteen different sites were investigated by the U.S.B.R.
The US Corporation for Engineering selected the site at Teton canyon and inspection of the site
began in 1957. The Bureau of Reclamation prepared a reconnaissance type report for the Teton
Dam in January 1961.Between 1961 and 1970 approximately 100 borings were taken on site.
Geological and seepage conditions were recorded and deemed acceptable for an earthen
embankment.
When the site was announced as suitable for the project, the construction contract including a water
pumping plant and irrigation of over 100,000 acres of farmland contract was awarded to the
Morrison-Knudson company of Idaho.
The site is on the Snake river Plain which is a large tectonic depression. The underlying layers
consist of rhyolitic and basaltic, late-Cenozoic volcanic rocks. This ash flow tuff sits on
sedimentary rock. This area is very permeable but no seepage was recorded during the preconstruction site investigation.
CONSTRUCTION:
The first step of construction was the design and implementation of the foundations. These
consisted of four different sections. They were as follows:
 Section 1: 21m deep trenches with steep sides on the abutments of the 1550m elevation.
 Section 2: A cutoff trench to the underlying rock below the 1550m elevation.
 Section 3: A grout curtain that ran along the foundations itself.
 Section 4: The extraction of the rock located beneath the abutments.
These sections were essential because the underlying rock type that was initially in place were not
completely suitable for this type of structure.
The Dam also needed 10 million m³ of material to fulfil the design of the structure. A great deal of
this was dredged from the river bed itself. There were 5 different sections to the dam. They were as
follows:
 Section 1:
Core: Moisture content 1.5% dry of optimum permeability 0.3 m/year.
 Section 2:
Compacted Sandy Gravel: Overlies Section 1.
 Section 3:
Miscellaneous Fill: Similar composition to that of Section 1.
 Section 4 and 5:
Rock Fill: Compacted on outer surface of dam.
Work on the Dam began in February 1972, a little over four years before the dam would eventually
fail. When completed, it would hold a reservoir of 356 million m³ of water. On October 3, 1975, the
Dam was sealed and the reservoir began to be filled. The construction process took just over 3 and
half years. However, the outlet works tunnel and the auxillary outlet works tunnel were not opened
at this time. This meant that the rising water rate went from the planned 0.3-0.6m per day up to 1m
per day. The USBR deemed that this was safe as long as the downstream water table and seepage
rate were measured on a more frequent basis.
FAILURE:
The seepage and water tables continued to be measured, but on June 3, 1976, several small leaks
were noticed in the northern section of the abutment wall. The USBR were notified and their
directions were to carry out more regular inspections every day with readings being noted twice a
week. One day following these appearances of seepage, there was a dampness area found with
small springs popping up in the right section of the abutment.
The next day saw a major leak appear with a flow rate of between 500 and 800 l/s with seepage
occurring 40m below the crest of the dam. A few hours later, workers tried to counteract a
whirlpool that had formed in the reservoir by shoving rip-rap structures into the sinkhole. Two
bulldozers were subsequently swallowed with the workers having to be rescued by there safety
lines. At this stage a 6m X 6m section of the dam had fallen into the whirlpool and with this, the
dam began to collapse.
Below, a sequence of the dam failure can be seen:
Over 300 million m³ of water pass through the broken dam and down into the Upper Snake River
Valley and flooded the towns and farms in Wilford, Sugar City, Rexburg and Roberts in Idaho.
AFTERMATH
Immediately after the disaster, the then president Gerald Ford rewarded $200 million in
compensation to those affected by the failure of the dam. This was to account for the 11 people
dead, 200 people left homeless, the thousands of cattle lost and millions of dollars in damage to
property. The Bureau of Reclamation set up a claims office; however $93.6 million dollars of the
claims were paid by the federal government.
After the failure of the Teton dam various commissions and boards were brought in to investigate
the causes of the Teton dam failure. An independent panel was selected by the Governor of Idaho to
investigate the failure. The panel went to work immediately and produced a report in 1976 outlining
the various possibilities and reasons for failure.
The panel concluded that the dam failed due to internal erosion of the core of the dam (i.e. piping
failure). A report that had been issued in 1947 by the US Bureau of Reclamation had indeed shown
that piping failure would occur at this site because the geological conditions were not suitable.
From these investigations, it’s clear that failure could have been avoided. The early geological
reports showed that the underlying volcanic rock was highly fractured and jointed and quite light
weight. Thus, this is why there was such a detailed foundation installed prior to construction of the
dam itself. The grout curtain failed in this catastrophe which meant that all these weak underlying
materials were simply washed away.
This tragedy has highlighted the importance of geology in engineering and geotechnical
engineering. Because of the quick fix approach that was taken to the poor quality rock type in the
valley, a massive engineering disaster occurred in such a small time-frame. This could have been
prevented if the site had been properly assessed. Thus, the Teton Dam failure has a model for other
such structures to learn from.