Unidentified man inspects a shinkage crack in the wing dike (right or western abutment) of the St. Francis Dam after it failed.
(Shrinkage cracks occur as concrete cures.)
The man is examining what appears to be oakum, a soluble fiber that expands when wet and is used to plug leaks. The trouble is, it's on the downstream (dry)
side of the dam.
"Oakum plugging would have been fine," says St. Francis Dam engineering expert J. David Rogers, "IF it had been applied on the upstream face of the dam.
Plugging the downstream face was, essentially, a potentially fatal flaw."
It's a bit like sticking your finger in a volcano to prevent it from erupting. You would need to cap it off from the inside.
Photograph shot on or shorly after March 13, 1928. The dam collapsed at 23:57:30 on March 12 and it took about 72 minutes for the 12.5-billion-gallon reservoir to empty (Outland 1977).
About the image: One of seventeen 5x7-inch glossy photographs found in a box in the Photography section of the San Francisco Public Utilities Commission's Engineering Archives in 2013. There was no record of the origin of the photographs and no writing on the back to identify subjects or dates. Current SFPUC staff members did not know the reason for their inclusion in the archive.
Ownership transferred via email communications (on file) from SFPUC to SCVTV-SCVHistory.com. Prints received July 11, 2014; subsequently transferred to the Santa Clarita Valley Historical Society.
1. A hand-written notation by current San Francisco PUC staff indicates the images were emailed Aug. 8, 2013, to someone who identified them as the St. Francis Dam. SFPUC staff alerted us to their existence in the Spring of 2014.
Construction on the 600-foot-long, 185-foot-high St. Francis Dam started in August 1924. With a 12.5-billion-gallon capacity, the reservoir began to fill with water on March 1, 1926. It was completed two months later.
At 11:57:30 p.m. on March 12, 1928, the dam failed, sending a 180-foot-high wall of water crashing down San Francisquito Canyon. An estimated 411 people lay dead by the time the floodwaters reached the Pacific Ocean south of Ventura 5½ hours later.
It was the second-worst disaster in California history, after the great San Francisco earthquake and fire of 1906, in terms of lives lost — and America's worst civil engineering failure of the 20th Century.