St Francis Dam

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File:St Francis Dam.jpg
The St. Francis Dam (looking north) with water in its reservoir

The St. Francis Dam was a concrete-arched gravity dam built as a large reservoir near the city of Los Angeles, California. The dam was built between 1924 and 1926 under the supervision of William Mulholland, an engineer for the Los Angeles Department of Water and Power. Minutes before midnight on March 12, 1928, the dam catastrophically failed. The resulting flood killed more than 400 people.

The need for the dam

Mulholland, a self-taught civil engineer and native of Ireland, had designed and built what was then the longest aqueduct in the world, taking water from Owens Valley and bringing it to Los Angeles, some 235 miles (380 km) away. The aqueduct supplied a surplus of water when it was completed in 1913. But Los Angeles grew at an amazing rate, and by 1920 more water was needed. Several small reservoirs were built in 1921 to supply the city in the event of a drought or damage to the aqueduct, but it was clear that a major reservoir was needed.

Mulholland had first considered the San Francisquito Canyon, about 30 miles (50 km) north of Los Angeles, as a potential dam site in 1911. The aqueduct ran conveniently along the canyon, and two electrical generating stations located there used aqueduct water to provide power for Los Angeles. The location appeared to be ideal, and not only because the reservoir would protect against drought; if the aqueduct were to be damaged by an earthquake or sabotage, the reservoir could provide ample water to Los Angeles until repairs could be made.

Construction

Today geologists know that the type of rock found in the San Francisquito Canyon is unsuitable for supporting a dam and a reservoir. But in the 1920s, two of the world's leading geologists at the time, John C. Branner of Stanford University and Carl E. Grunsky, found no fault with the San Francisquito rock. The dam was built squarely over the San Francisquito earthquake fault, although this fault has since been inactive.

In 1924, construction began on the St. Francis Dam, which was given an anglicized version of the name of the creekbed on which it rested. The project began quietly so that the farmers dependent on the water of the San Francisquito Creek wouldn't notice the dam and try to stop the construction.

Major alterations

The St. Francis Dam was designed to be 175 feet (53 m) tall and to hold back a reservoir of 30,000 acre-feet (37 million m³). Immediately after construction began in 1924, Mulholland decided to raise the dam 10 feet (3 m) and increase the capacity of the reservoir to 32,000 acre-feet (39 million m³). Since little construction had been done some minor changes were made in the design to accommodate the change. However, in July of 1925, when the dam was about halfway completed, Mulholland again decided to raise the dam another 10 feet (3 m) to a total height of 195 feet (59 m). A "wing dyke" had to be constructed on the western side of the dam to keep water from spilling over a low ridge when the reservoir filled. The new capacity was 38,170 acre-feet (47,080,000 m³).

Gravity dams, like the St. Francis Dam was, use their weight to resist the water pressure exerted on them. The St. Francis Dam was increased in height from the designed 175 feet (53 m) to 195 feet (59 m) at completion, without any substantial widening of the dam's base. Such changes would not occur with modern engineering practices, but little was said about the changes in 1925.

Sabotage

In 1927 a few people in Owens Valley who were fighting the California Water Wars dynamited the Los Angeles Aqueduct several times. The St. Francis Dam and Reservoir saved Los Angeles from a severe water shortage and water from the reservoir also generated electricity. Mulholland called the dam "providential."

During the height of the Water War there was a threat made against the St. Francis Dam and an anonymous informant pleaded to the Los Angeles police to "get some officers up there quick." Fortunately no attempt was made to dynamite the dam.

Prelude to failure

Several cracks appeared in the dam throughout 1926 and 1927. Some began to leak. Mulholland inspected these cracks and found them to be of no consequence. All concrete dams form cracks over time.

On March 7, 1928, the St. Francis Reservoir was completely filled for the first time. New leaks were discovered by the damkeeper, Tony Harnischfeger, but Mulholland was convinced they were relatively minor.

Another factor in the failure could have been the construction of a new road along the east abutment, which was over the ancient landslide. Blasting with dynamite for the new road was done right up until March 8, 1928, and much of it right next to the unstable abutment. It is unknown if the blasting could have loosened the rock or not.

On the morning of March 12, Harnischfeger discovered a new leak and worried that it was undermining the dam. Mulholland, his son Perry, and assistant Harvey van Norman investigated. Perry thought the leak looked serious, but Mulholland felt it to be typical of concrete dams, and declared the leaks safe.

Failure

File:Destroyed St Francis Dam.jpg
The dam after the breach.

The dam finally crumbled at 11:57 p.m. on March 12, 1928, scarcely 12 hours after Mulholland had inspected it. There were no surviving eyewitnesses to the failure, but one man on the road about a half mile (1 km) away from the dam recalls feeling a strange shaking of the ground and the sound of "crashing, falling blocks." The shaking he felt was no earthquake (seismographs recorded no significant earth movements) but rather the tumble of incredibly heavy pieces of concrete that were falling off the dam.

Exactly how and why the dam failed has never been completely determined. J. David Rogers, a professor of geological engineering at the University of Missouri-Rolla has published the most comprehensive account of the dam's failure, which he says was caused by uplift, the instability of the paleomegalandslide, and Mulholland's unwise raising of the dam's height. Later analysis of the remaining concrete has shown that insufficient water was used in its preparation, making it brittle, which was likely a contributing factor in the collapse.

Tony Harnischfeger was probably the first to die in the floodwave, which was about 125 feet (38 m) high when it hit his little cottage in the San Francisquito Canyon. His body was never recovered.

The disaster

Twelve billion US gallons (45 million m³) of water surged down the San Francisquito Canyon, crushing the heavy concrete walls of a hydroelectric power plant and sweeping away everything else in its path. The flood continued down the San Francisquito then into the Santa Clara River bed. The towns of Castaic Junction in Los Angeles County and Fillmore, Bardsdale, and Santa Paula in Ventura County were hit especially hard.

Bravery was seen in the actions of telephone operators and motorcycle policemen who notified people in their homes of the dangers, until the rising floodwaters forced them to retreat.

The aftermath

The exact number of dead remains unknown to this day. The official count made in August 1928 stood at 385. However more bodies were discovered every few years until the 1950s, and the remains of another victim were found deep underground near Newhall in 1992. It is generally accepted that the death toll was between 400 and 500.

Mulholland shouldered all the blame willingly. He was so easily made a scapegoat that the initial investigations weren't as thorough as they might have been. Although Mulholland accepted the blame, he hinted during his trial for manslaughter that he felt the dam was sabotaged.

The dam was not rebuilt. Several large pieces of concrete were not swept away by the waters, including the center section of the dam which remained standing upright. After the death of a young man, who fell from a large piece of concrete while exploring the ruins two months after the failure, the remains of the dam were dynamited and jackhammered into oblivion.

Today all that remain are a few weathered chunks of gray concrete and the rusted remains of the handrails that lined the top of the dam. The ruins are easy to see from the San Francisquito Canyon Road, about five miles (8 km) north of the city of Newhall.

L.A. based rock musician, Frank Black, has made several references to the disaster in his songs, including the tracks "St. Francis Dam Disaster" and "Olè Mulholland".

Further reading

  • Outland, Charles F. Man-Made Disaster: The Story of St Francis Dam. A.H. Clark Company: 1977.
Outland's study of the dam and the ensuing flood, first published in 1963, is the only widely published comprehensive work about the dam, the failure, and the disaster. This book is the result of good original research. An expanded edition is available from the Historical Society of Southern California.
  • Nunis Jr., Doyce B. (Ed.). St. Francis Dam Disaster Revisited. Historical Society of Southern California. 2002. ISBN 0914421271.
This collection of articles about the dam includes contributions from Catherine Mulholland, William Mulholland's granddaughter, and Dr. J. David Rogers. It is the only other book on the St. Francis Dam in print today.

See also

External links

de:St.-Francis-Talsperre