Orange County Branch Newsletter

July 2019

ASCE OC YMF

St. Francis Dam Tour

By Joe Sinkiewicz | YMF Programs Committee Co-Chair



This valley typifies the sort of standard beauty of the foothills that hem in the communities of Southern California. Grass and sturdy brush blanket the width of the valley as it weaves upward to the pass that has long connected the San Juaquin and Santa Clarita Valleys. At its bottom, ancient oaks nestle a trickling stream which has come to know the company of a twisting road. A road with all the fidgeting and persistence of a path carved by hand for the stagecoaches of our recent past. Yet this valley is unlike its neighbors. Unsettling outcroppings of unnatural stone punctuate its floor, and the stream trickles painfully over an unfamiliar bed. The valley bears it all: the stone, the stream, and the lost remains of hundreds of people. This is the San Francisquito Valley, the site of the deadliest US civil engineering disaster of the 20th century.

The St. Francis Dam once stood 210 feet tall across this valley. Its characteristic "stair step" facade is still visible in the debris.

Kimo Look of the ASCE Metropolitan Los Angeles Branch hosted a historical walking tour of the dam disaster site. His passion for the stories and lessons was infectious. Mr. Look brought pages of references and provided binders of historical photos, diagrams of the dam and surrounding hills, and charts to help attendees understand the context of the disaster in the decades leading up to the collapse and the effects the dam has on our lives and careers to this day.

The completion of the Los Angeles Aqueduct in 1913 brought water to Southern California from Northern California. The project was never popular with the residents and ranchers of the Owens Valley, and the aqueduct was attacked, sabotaged, even dynamited several times. Coupled with the drought of 1920, it became clear to the Los Angeles Bureau of Water Works and Supply that the city’s water would need storage to remain secure.

A huge chunk of the St. Francis Dam deposited over 1/4 mile downstream.

The Bureau set out to build a local reservoir that could hold one year’s worth of water for the growing communities of Southern California. They chose the San Francisquito Valley which had a naturally narrow spot ideal for locating a dam. The Saint Francis dam was one of the tallest dams in the world at 190 feet. As the population grew, so did the dam and it was raised an additional 20 feet higher than originally designed.

Near midnight on March 12, 1928, the dam collapsed catastrophically, sending a wall of water 140 feet tall thundering down the valley. The body of the dam keeper living at the base of the dam was never found. As the water pushed through the valley, it incorporated huge boulders, trees, even parts of the dam and became a 50-foot-tall debris flow, churning, crushing, and scouring everything in its path. At 18 miles per hour, it beset the small community of power plant workers and their families living one and a half miles downstream of the reservoir at Powerhouse 2. One man, unable to sleep noticed a strange mist flowing over the town. When he heard a distant rumbling, he pulled his wife and son out of bed and told them to run uphill as fast as they could. He was returning to save his daughter when the wave struck the town. 64 of the 67 inhabitants were killed as they laid in their beds only 5 minutes after the collapse.

Abandoned road leading to the site.

Five miles downstream a camp of about 150 linemen for Southern California Edison was sleeping in tents. Those that had the tent flaps secured floated and survived, while those sleeping with their tents opened drowned, 84 in total.

A driver was caught off guard as the wave picked his car right off the road. He escaped the vehicle and managed to run to a phone to warn the people of the Santa Clarita Valley of the destruction that was coming. A highway patrolman happened upon a migrant camp downstream of the imminent flood. Unable to speak Spanish, all the patrolman could muster was, “Mucho aqua!” The workers, looking at the clear night sky, did not see any potential for a flash flood. The patrolman ultimately gave up and left to warn other towns. Given the migratory nature of the workers, it is still not known how many of them died, but some estimates are over one hundred. It took only 70 minutes to drain the entire reservoir, and when the water finally subsided, between 450 and 600 people were dead. Only 150 bodies were recovered. 

Debris from the disaster still litters the valley floor.

The public demanded a reason for the collapse and an inquiry gave them one. The official reason for the disaster was attributed to a known fault along the west side of the dam, despite the fact that no seismic activity was observed in the area on the night of the collapse. A viable theory for the collapse did not emerge until the 1980s. The causes of the collapse involved concepts that were not yet known to engineers at the time. The concrete was poured in massive lifts creating large thermal cracks in the dam. It was the memory of the St. Francis dam that taught the designers of the Hoover dam to refrigerate the mass concrete as it cured. The aggregate of the St. Francis dam concrete was pulled directly from the stream bed. This rock was weak, of wildly variable size, and was poured unwashed into the cement. It would take decades before engineers came to realize the consequences of such practices. The collapse of the St. Francis dam served as the impetus for licensing requirements for engineers in the State of California.

The world owes a heavy debt to the painful peace of the San Francisquito valley and to the souls whose bodies were buried by the manmade maelstrom; buried because of man, but not by hand.

The obvious difference in soil color marks the seismic fault line that was initially blamed for the disaster.

About the Author

Joe Sinkiewicz is a civil engineer and building enclosure consultant with degrees in structural engineering and physics from UC San Diego. Outside of work, Joe enjoys growing live plants in his aquariums and avoiding exercise. Joe can be reached at [email protected] or LinkedIn.


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