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Sunday, March 06, 2016

Hydroelectric failure #2 -Teton Dam

Here's a nice picture taken from a helicopter on June 5, 1976.  This is Teton Dam in Eastern Idaho, in the process of collapsing and killing 11 people and 35,000 head of cattle.
Image courtesy of wikipedia, Photographer/Maker: Roberts ID-L-0010, WaterArchives.org

Technically, this isn't a "hydroelectric failure".  There were no electrical generators installed in the dam.  It was new and had been built for flood control, with a power station to be added later.

A couple of interesting facts about Teton Dam (location)
  1. It didn't quite manage to complete its initial fill before it failed.
  2. The dam was built against rock that had fissures (actual 100ft long, 11ft wide caves) that could be entered by a person. 
 Below is a Google Earth image showing the location of Teton Dam.  The Grand Teton mountains  are to the right and Yellowstone National Park is to the top right.

A close up image of the remaining spillway.  The dam was (wisely) not rebuilt.

The Wikipedia article tells the debacle of the engineering problems better than I ever could, so I will just paste portions here.  I will bold and underline what would seem to be giant red flags for a hydro engineer.
Geology:
The eastern Snake River Plain is almost entirely underlain by basalt erupted from large shield volcanos on top of rhyolitic ash-flow tuff and ignimbrites. The tuff, a late-Cenozoic volcanic rock is 1.9 million years old. The dam site is composed of basalt and rhyolite, both of which are considered unsuitable for dam construction because of their high permeability. This was confirmed by long term pump-in tests at rates of 165 to 460 US gallons (620 to 1,740 litres) per minute.
Test cores, drilled by engineers and geologists employed by the Bureau of Reclamation, showed that the rock at the dam site is highly fissured and unstable, particularly on the right side of the canyon. The widest fissures were determined to be 1.7 inches (4.3 cm) wide. The Bureau planned to seal these fissures by injecting grout into the rock under high pressure to create a grout curtain in the rock.
In addition, an investigation of the area by geologist of the U.S. Geologic Survey indicated that it was seismically active: five earthquakes had occurred within 30 miles (50 km) of the dam site in the previous five years, two of which had been of significant magnitude. This information was provided to the Bureau of Reclamation in a memorandum, but the geologists' concerns were considerably watered down in the six-month re-drafting process before the USGS sent the final version of the memo to the USBR in July 1973.

In 1973, when the dam was only half-built, but almost $5 million had already been spent on the project, large open fissures were encountered during excavation of the key trench near the right end of the dam, about 700 feet (210 m) from the canyon wall. The two largest, near-vertical fissures trend generally east-west and extend more than 100 feet (30 m) below the bottom of the key trench. Some of the fissures are lined by calcite, and rubble fills others. Several voids, as much as 6 inches (15 cm) wide, were encountered 60 to 85 feet (18 to 26 m) below the ground surface beyond the right end of the dam and grout curtain.
The largest fissures were actually enterable caves. One of them was eleven feet (3.4 m) wide and a hundred feet (30 m) long. Another one was nine feet (2.7 m) wide in places and 190 feet (60 m) long. These were not grouted because they were beyond the keyway trench and beyond the area where the Bureau had decided grouting was required. This necessitated using twice as much grouting as had been originally anticipated – 118,000 linear feet were used in total. Later, the report of a committee of the House of Representatives which investigated the dam's collapse felt that the discovery of the caves should have been sufficient for the Bureau of Reclamation to doubt its ability to fill them in with grout, but this did not happen: the Bureau continued to insist, even after the dam had failed, that the grouting was appropriate.

As you might have guessed from the very first image, this project did not end well.  Note the bulldozer on the upper face of the dam attempting to move in and repair the damage.  The driver survived.  Source (WP:NFCC#4)

Bulldozer toppling in.



The dam cost $100 million to build, and cost $300 million in damage.  It destroyed the downstream river habitat, in addition to the lives lost and property damage.

Wiki again (on the damage):

When the dam failed, the flood struck several communities immediately downstream, particularly Wilford at the terminus of the canyon, Sugar City, Salem, Hibbard and Rexburg. Thousands of homes and businesses were destroyed. The small agricultural communities of Wilford and Sugar City were wiped from the river bank. Five of the fourteen deaths attributed to the flood occurred in Wilford.
The similar community of Teton City, on the south bank of the river, is on a modest bench and was largely spared. One Teton resident was fishing on the river at the time of the dam failure and was drowned. An elderly woman living in Teton City died as a result of the evacuation.
One estimate placed damage to Hibbard and Rexburg area, with a population of about 10,000, at 80 percent of existing structures. The Teton River flows through the industrial, commercial and residential districts of north Rexburg. A significant reason for the massive damage in the community was the location of a lumber yard directly upstream. When the flood waters hit, thousands of logs were washed into town. Dozens of them hit a bulk gasoline storage tank a few hundred yards away. The gasoline ignited and sent flaming slicks adrift on the racing water. The force of the logs and cut lumber, and the subsequent fires, practically destroyed the city.
The flood waters traveled west along the route of the Henry's fork of the Snake River, around both sides of the Menan Buttes, significantly damaging the community ofRoberts. The city of Idaho Falls, even further down on the flood plain, had time to prepare. At the older American Falls Dam downstream, engineers increased discharge by less than 5% before the flood arrived. That dam held, and the flood was effectively over, but tens of thousands of acres of land near the river were stripped of fertile topsoil.
The force of the failure destroyed the lower part of the Teton River, washing away riparian zones and reducing the canyon walls. This seriously damaged the stream's ecology and impacted the native Yellowstone cutthroat trout population. The force of the water and excessive sediment also damaged stream habitat in the Snake River and some tributaries, as far downstream as the Fort Hall bottoms.
A few pictures of the aftermath:  Keep in mind this isn't an act of nature, it's an engineering screw-up.










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