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At 11:57 pm on March 12, 1928, the St. Francis Dam collapsed, releasing 39 million cubic meters of water into the San Fransisquito Canyon. By the time the flood reached the ocean 5 ½ hours later, over 600 people were dead, 10,500 acres of crops had been lost, and 9 communities were damaged or wiped out. It remains the second-greatest loss of life in California, next to the 1906 San Francisco Earthquake.

How It Happened

William Mulholland, the Chief Engineer for the Los Angeles Bureau of Water Works, began construction on the St. Francis Dam in 1924 to provide reservoir capacity for the Los Angeles Aqueduct. The dam was to be 56 meters high; however, in 1924 he raised the dam’s height by 3 meters, and in 1925 by another 3 meters and an eastern abutment, to bring the dam’s eventual diumensions to 62 meters height, 213 meters length, with a top thickness of 4.8 meters and a bottom thickness of 53.3 meters. It was a concrete-block, arched, gravity-fixed dam, the same type as the Mulholland Dam. The reservoir held 47 million cubic meters of water, weighing an estimated 52 million tons. It rested at 559 meters above sea level.

The St. Francis Dam reached full capacity for the first time on March 7, 1928. By March 12, motorists noted that a road by the dam had sagged by .3 meter. Cracks and leaks were sighted in the dam by Mulholland and others; Mulholland inspected them and pronounced them safe.

At 11:57 pm the dam collapsed; any eyewitnesses to the event were killed. Both east and west ends of the dam fell, leaving a twisted central section standing. The entire reservoir emptied in 70 minutes, sending a flood wall 38 meters high down the canyon at 18 km/hr. Peak outflow was an estimated 14,160 meters/second. The wave roared through the communities of Valencia, Newhall, Castaic Junction, Piru, Saticoy, Fillmore, Bardsdale,  and Santa Paulo, emptying into the Pacific Ocean at Montalvo, 87 km away from the dam, at 5:30 am.

The Aftermath

The St. Francis Flood killed an estimated 600 people. The exact number was never known, since bodies washed out to sea or were trapped under wreckage. Bodies were discovered as far away as Mexico, deep underground, and as late as the 1050’s. The San Francisquito Canyon was a camping place for itinerant farm workers, adding to the uncertain count.

The flood left up to 20 meters of mud and debris on fields and farms, ruining 10,500 acres of crops. 1200 homes were damaged, and 10 bridges destroyed.

Investigation revealed that an undiscovered, ancient landslide had lifted and shifted the dam under the new pressure of water and concrete. Mulholland claimed full responsibility, but was exonerated by the inquest.

Links

http://www.usc.edu/libraries/archives/la/scandals/st_francis_dam.html

http://www.scvhistory.com/scvhistory/index2.htm

http://www.sespe.com/damdisaster/index.html

 

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