The Center for Land Use Interpretation

FIELD REPORT: Dam Failures
Preliminary Report From an Ongoing Investigation

The middle section of the Teton Dam remains as a pyramidal mound in the high plains of Idaho. CLUI photo

There are thousands of dams in the United States, from the massive concrete structures on the Columbia River to the earthen tailings empoundments of mining operations. Most lakes in this country are in fact artificially formed by dams, which back up drainage corridors for reservoirs and flood control purposes. And of course, when these ubiquitous structures fail, it can lead to the catastrophic loss of life and property, sometimes wiping whole towns off the map.

Hundreds of dams have failed in America (including one near the CLUI Los Angeles Office - the Baldwin Hills Dam, which broke in 1963, killing five people), but three incidents stand out for their magnitude and the severity of the disastrous effects of their failure. And at each of these sites, impressive remains of the broken dams remain visible.

The Teton Dam Failure

Despite much local opposition, as there was considered to be insufficient reason to build the dam, the Bureau of Reclamation completed the Teton Dam, along the Teton River in southeastern Idaho, in 1975. The primary need cited for the dam, ironically, was for flood control. Over the next several months the reservoir slowly filled to capacity, with a maximum depth of 240 feet. Within days of reaching capacity, with water coursing over the spillway, the dam broke, on June 5, 1976.

Seepage was reported and inspected the day before the failure, and work crews attempted to fill growing breaks in the dam minutes before it gave out, fleeing on foot as the widening gap swallowed their bulldozers. When the full collapse came, the flood downstream killed at least 11 people (more were said to die from heart attacks related to the flood), and destroyed thousands of buildings. The largest town affected was Rexburg, 12 miles from the dam (population 10,000), which was as much as 80% destroyed, as were the small agricultural towns of Sugar City, Wilford, Salem, and Hibbard. Nearly half a billion dollars in claims were levied against the Bureau of Reclamation. Though the affected area was large, the water spread out quickly on the flat floodplain, dissipating the force of the water.

South Fork Dam Failure

The rolling hills and deep valleys in western Pennsylvania worked against the ill-fated town of Johnstown, which experienced the worst dam failure disaster in US history. On May 31, 1889, when the South Fork Dam gave out, 14 miles upstream, the impounded Lake Conemaugh rushed down the steep valley, snowballing into a battering-ram of debris. Though it took the front nearly an hour to hit Johnstown, the force and mass was tremendous. The wall of water and debris cleared everything in its path, washing up the hill on the other side of town, and bouncing back to cause more wreckage. A stone railroad bridge finally stopped a major part of the front as the force dissipated, forming a 60 acre field of debris, which included buildings, railcars, spilled oil, and hundreds of people, alive and dead, who were swept into the flood. The debris soon caught fire, and burned for five days. Total loss of life from the flood was over 2,200.

The break in the South Fork dam is still visible, 14 miles upstream from Johnstown, Pennsylvania. CLUI photo

All earthen dams will collapse if water is allowed to spill over the top the dam, as the erosive force of the water quickly eats away at the loose material. For this reason spillways, which channel water around the dam if the water level gets too high, are especially important. But the night before the Johnstown Flood, as rain filled the reservoir at a rate of a foot per hour, the spillways of the South Fork Dam were completely clogged.

Several years earlier, the dam and the property around the lake had been purchased and turned into an exclusive resort called the South Fork Hunting and Fishing Club. In order to keep the fishing stock of imported black bass in the lake, an iron screen had been placed over the spillway gates. This screen, however, also kept small debris from passing over the spillway so that, by the night of the big rains, the spillways were uselessly blocked, and the water eventually overtopped the dam, causing it to fail.

Andrew Carnegie, whose steel empire settled much of western Pennsylvania, visited the ruins of the old steeltown of Johnstown soon after the flood. He had a grand library built on the site where the old library had stood, before it was washed away. In 1976, the building became a museum devoted to telling the Johnstown Flood story. This was especially fitting as Carnegie was a member of the South Fork Fishing and Hunting Club.

St. Francis Dam Failure

Johnstown was one of the worst American civil engineering disasters of the 19th Century, but the St. Francis Dam failure was possibly the worst of the 20th Century. 500 people were killed when the dam broke in 1928, with water rushing for 54 miles down the Santa Clara River Valley to the ocean at Ventura, California. The first community struck was Castaic, said to have been "swept clean as a pool table." A few minutes later, a power company camp in the river valley was washed away, killing 84 people. Then portions of the towns of Piru, Fillmore, Santa Paula and Saticoy were demolished. Bodies later washed up on the beaches of San Diego, and were still turning up as late as the 1970's, when a local journalist exploring the river, stumbled on a Model A Ford, emerging from the sandy riverbed, with two skeletons inside.

Concrete ruins from the St. Francis Dam remain where they fell on site after the 1928 flood. CLUI photo

Though the cause of the failure is still debated by some, William Mulholland, whose water agency built the dam, accepted full responsibility. He had been at the dam 12 hours before it failed, to inspect some reported leaks, and declared it safe. The hero of the Owens Valley Aqueduct, which made the rapid development of Los Angeles possible, retired in disgrace after the St. Francis Dam failure, saying he envied the dead.

Despite continued improvements in engineering and emergency response brought on by these disasters, dams continue to threaten populations. In 1979, a dam failure along the Machu River in India left 5,000 dead, and 268 were killed in 1985 when the Stava Tailings Dam in Italy broke. And in Los Angeles, 80,000 people were evacuated when the Lower San Fernando Dam nearly failed in the 1971 earthquake.

In each case, remnants of the South Fork Dam, the Teton Dam, and the St. Francis Dam remain on site, at the foot of their respective empty reservoir basins, haunting physical evidence of the limitations of artificial terrestrial engineering.