St. Francis Dam

from Wikipedia, the free encyclopedia
St. Francis Dam
Site plan of the reservoir
Remains Today (2009)

Coordinates: 34 ° 32 ′ 49.3 "  N , 118 ° 30 ′ 45.4"  W.

The St. Francis Dam was a curved concrete gravity dam with a large reservoir near Los Angeles , California . The dam was built from 1924 to 1926 under the direction of William Mulholland , an engineer with the Los Angeles Department of Water and Power. The dam broke a few minutes before midnight on March 12, 1928. The resulting tidal wave killed between 550 and 600 people.

The benefits of the dam

Mulholland, a self-taught civil engineer and native Irishman, designed and built the world's longest aqueduct at 380 km from Owens Valley to Los Angeles. Since its completion in 1913, this served as a water supply for Los Angeles. But the city grew so quickly that more water was needed from 1920. Several smaller reservoirs were built in 1921 to supply the city in the event of drought or damage to the aqueduct, but an even larger reservoir was needed.

Mulholland had already seen the San Francisquito Canyon, about 50 km north of Los Angeles, as a possible site for a dam in 1911. The aqueduct ran along the canyon, and two generator stations used water from the aqueduct to generate electricity for Los Angeles. The location seemed ideal, not only because the reservoir would protect against a drought, but also because it could bring replacement water to Los Angeles if the aqueduct were damaged or sabotaged by earthquakes .

The construction of the dam

Today geologists know that the rock in the San Francisquito Canyon is unsuitable on which to build a dam system. But in the 1920s, two of California's leading geologists and civil engineers, John C. Branner of Stanford University and Carl E. Grunsky , found no faults in the rock. The dam was even built directly over the San Francisquito earthquake fault, although it is still inactive today. Grunsky was one of those commissioned to investigate the causes of the dam failure in 1928, along with his son EL Grunsky and Stanford University geologist Bailey Willis. They found that the soil on the east side in particular was unsuitable, since there was an old landslide in the subsoil and there was a mica schist interspersed with numerous cracks, which swelled due to seepage water and thus led to uplift.

In 1924 the construction of the St. Francis Dam began; the name is an Anglicized version of the river name. The project began clandestinely so that the farmers who needed the water from San Francisquito Creek would not notice the dam and stop construction.

Significant changes

The St. Francis dam was to be 53 m high and contain a storage space of 37 million m³ (30,000 acre feet). Immediately after the construction work began, Mulholland decided to increase the dam wall by three meters and the capacity to 39 million m³. Since not much had been built yet, only minor changes were necessary. But then, in July 1925, when the dam was halfway finished, Mulholland decided to raise the wall again by three meters to a total of 59 meters. A wing dam therefore had to be built on the western side so that the water did not overflow sideways. The new storage space size was 47 million m³ (38,170 acre-feet).

Weight dams like the St. Francis dam or like the Hoover Dam today ( arch weight dam ) use their own weight to withstand the water pressure. The St. Francis dam had been increased from 53 to 59 m without its width being increased significantly.

The water war

In 1927 there were some people in Owens Valley who waged the so-called California Water War and several times blew up the Los Angeles Aqueduct with dynamite. The St. Francis Dam saved Los Angeles from drought during this period; in addition, electricity was generated with the water from the reservoir. Mulholland called the dam "providential", which means something like "providence".

At the height of the water war, the St. Francis Dam was also threatened. An anonymous caller asked the police to quickly send some officers there. But no attempt was made to blow up the dam.

Break of the dam wall

prehistory

In 1926 and 1927 there were various cracks in the dam. Some started to lick. Mulholland inspected these cracks and found them meaningless, because all concrete walls crack over time.

On March 7, 1928, the reservoir was completely filled for the first time. New leaks were discovered by the dam master Tony Harnischfeger, but Mulholland was convinced that they were relatively insignificant.

Another cause of the failure could be the construction of a new road along the eastern abutment, which was built on an old landslide area. Up until March 8, 1928, the road construction site was blasted with dynamite, and much of it right next to the unstable abutment. It is unknown whether the blasting could have loosened the rock.

On the morning of March 12, the dam master Harnischfeger discovered a new leak and was concerned that it could undermine the dam. Mulholland, his son Perry and his assistant Harvey van Norman came for an investigation. Perry thought the leak was serious, but Mulholland thought it was typical of concrete dams and declared it safe.

The break

The dam failed at 11:57 p.m. on March 12, 1928, around twelve hours after Mulholland inspected it. There were no surviving eyewitnesses to the break, but a man on the road a kilometer away later remembered a strange shaking of the ground and the sound of tumbling, falling stones. The tremors he felt were not an earthquake ( seismographs did not record any significant earth movement), but rather the falling of extremely heavy pieces of concrete that fell from the dam.

It was never established exactly how and why the dam failed. The engineer and geologist J. David Rogers has published the most comprehensive description of the fracture, which in his opinion, the buoyancy , the instability of the old landslide area stemmed and imprudent wall increase.

The tidal wave

45 million cubic meters of water tumbled down San Francisquito Canyon, crushing the heavy concrete walls of a hydroelectric power station, and washing away everything on its way. The tide continued in the Santa Clara River. The towns of Castaic Junction in Los Angeles County, Fillmore, Bardsdale, and Santa Paula in Ventura County have been particularly hard hit.

The dam master Tony Harnischfeger was probably the first to perish in the 38-meter-high tidal wave when it hit his small accommodation in San Francisquito Canyon. His body was never found.

The telephone operators and policemen on motorbikes showed bravery, warning the population of the danger until the rising tide forced them to retreat.

Aftermath

The exact number of victims remains unknown to this day. The official census of August 1928 showed 385 deaths. However, more bodies were discovered each year until the 1950s, and the remains of one more victim were not found deep in the ground near Newhall until 1992. Generally recognized is a number between 550 and 600 deaths.

Mulholland willingly accepted all the guilt. In the subsequent legal hearing on the disaster, however, he still considered it possible that the dam could have been sabotaged. The investigation reports by Grunsky and Willis came to the conclusion that according to the state of the art at the time, unpredictable weaknesses in the subsurface were primarily responsible (see above). Mulholland was acquitted of criminal guilt in the official investigation, but it was recommended that no one else should be solely responsible for the design and construction of dams. Mulholland subsequently resigned from office in 1929. The mistrust of the public led to the dams for which he was responsible (such as the Mulholland Dam in Hollywood) and other water supply structures being subjected to a thorough investigation and, in some cases, reinforced.

The dam has not been rebuilt. Various large pieces of concrete did not wash away, including the central section of the dam, which remained upright. Following the death of a young man who fell from a large piece of concrete while scouting the ruins two months after it broke, the remains were blown up and broken to pieces with a jackhammer.

What remains today are a few weathered fragments of gray concrete and rusted remains of the railings on the top of the wall. The ruins are easy to see from San Francisquito Canyon Road, approximately 5 miles north of Newhall town.

Artistic processing

The break of the dam is the subject of the song St. Francis Dam Disaster by Frank Black (2001).

National Monument and National Memorial

On March 12, 2019 with the signing of the Congress-law John D. Dingell, Jr. Conservation, Management, and Recreation Act by President Donald Trump on separate surfaces a US National Monument named Saint Francis Dam Disaster National Monument and a Saint Francis Dam Disaster National Memorial . Both areas are managed by the United States Forest Service within the Angeles National Forest .

literature

  • Norris Hundley, Donald C. Jackson: Heavy Ground: William Mulholland and the St. Francis Dam Disaster , University of California Press 2015
  • Charles F. Outland: Man-Made Disaster: The Story of St Francis Dam . AH Clark Company, 1977. (Outlands Study of the Dam and the Subsequent Flood, first published in 1963, is the only comprehensive work on the Dam, Rift, and Disaster)
  • Doyce B. Nunis Jr. (Ed.): St. Francis Dam Disaster Revisited . Historical Society of South California, 2002, ISBN 0-914421-27-1 . (A collection of articles on the dam, including contributions by Catherine Mulholland, William Mulholland's granddaughter, and Dr. J. David Rogers. One of the two books on the St. Francis Dam available today)
  • John Nichols: St. Francis Dam Disaster . Arcadia Publ., 2002, ISBN 0-7385-2079-9 . (Photo documentation with over 200 commented contemporary photos about the consequences of the dam breach)
  • Fred A. Noetzli: The break of the St. Francis dam in California . Swiss construction newspaper. Volume 91, No. 16, April 21, 1928, pp. 193-196.

See also

Web links

Commons : St. Francis Dam  - collection of pictures, videos and audio files

Individual evidence

  1. ^ Norris Hundley, Donald C. Jackson: Heavy Ground: William Mulholland and the St. Francis Dam Disaster , University of California Press 2015, pp. 296ff
  2. ↑ St. Francis Dam Desater , Water and Power Associates
  3. ↑ John D. Dingell, Jr. Conservation, Management, and Recreation Act