March 12, 1928: St. Francis Dam Disaster

Portion of the St. Francis Dam after the catastrophic failure

March 12, 1928: St. Francis Dam gives way in Los Angeles, killing over 500 people. “The St. Francis Dam was a curved concrete gravity dam, built to create a large regulating and storage reservoir as part of the Los Angeles Aqueduct. It was located in San Francisquito Canyon, about 40 miles northwest of Los Angeles, California, approximately 10 miles north of the city of Santa Clarita….

The dam was designed and built between 1924 and 1926 by the Los Angeles Department of Water and Power, then named the Bureau of Water Works and Supply. The department was under the supervision of its General Manager and Chief Engineer, William Mulholland.

At two and a half minutes before midnight on March 12, 1928 the dam failed catastrophically and the resulting flood killed up to 600 people. The collapse of the St. Francis Dam is considered to be one of the worst American civil engineering failures of the 20th century and remains the second-greatest loss of life in California’s history, after the 1906 San Francisco Earthquake and fire. The disaster marked the end of Mulholland’s career….

As the dam collapsed, the reservoir’s 12.4 billion U.S. gallons of water began to surge down San Francisquito Canyon in a dam break wave….”

Five minutes after the collapse, having traveled a distance of one and one-half miles at an average speed of 18 miles per hour, the now 120-foot-high flood wave destroyed the heavy concrete Powerhouse No. 2 and took the lives of 64 of the other 67 workmen and their families who lived nearby. The water traveled south down the canyon and began emptying into the Santa Clara riverbed. The amount of water was too great and caused it quickly to begin overflowing its banks, flooding parts of present-day Valencia and Newhall. The deluge, now 55 ft high, was generally following the course of the river bed west. In doing so, hit and demolished Southern California Edison Saugus substation, leaving the entire Santa Clara River Valley and part of the city of Ventura without power.

At this time, near 1:00 AM, at least four miles of the state’s main north-south highway (now Interstate 5) was under water and a short distance away, near what is presently the area around Six Flags Magic Mountain amusement park to State Route 126, the flood was washing away the town of Castaic Junction. At a speed of 12 mph the water continued on and entered the valley. Approximately five miles downstream, near the Ventura and Los Angeles county line, on the flats of the river bank the Edison Company had set up had a temporary construction camp for its 150 man crew. Due to miscommunication and confusion among the Edison personnel, no warning was sent and 84 of them died.”

Guest Commentary: The dam collapse destroyed Mulholland who took the blame for it. However, neither the technology nor geologic understanding at the time existed that would have revealed that one of the dam’s abutments was tied into an ancient landslide. The reservoir saturated that slide and it gave way. The true cause of failure was not known until decades after the collapse. Mulholland went to his grave with the burden of nearly 500 needless deaths for which he felt responsible. (from Byron Buck, 3/12/16)

St. Francis Dam before the failure

Photo: Portion of the St. Francis Dam after the catastrophic failure AND St. Francis Dam before the failure

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