Deadly Flooding in the San Francisquito Canyon
Tom Mulholland and the St. Francis Dam Disaster in 1928
Oct 14, 2009
At 11:57:30 PM on March 12, 1928, the St. Francis Dam failed, sending a 180 foot high wall of water crashing down the southern California canyon.
The exact time was noted at the power house due to the abrupt termination of the turbine-produced electricity at the instant the rupture occurred. Without electrical power, no one downstream of the dam could be warned of the impending calamity in time to evacuate.
By the time the floodwaters hit Santa Paula, 42 miles south of the dam, the water surge was approximately 25 feet deep. An estimated 500 people died by the time the floodwaters reached the Pacific Ocean, 54 miles away near Ventura, at about 5:30 AM.
The Damage Cost and the Death Toll
An accurate death toll was never reached because many of the casualties were migrant workers. As late as 1994, the remains of a victim were found buried in a 30-foot-deep silt bed which was deposited by the flood waters. As dawn broke over Southern California, parts of Ventura County lay under 70 feet of mud and debris. The towns of Castaic Junction, Piru, Fillmore, and Santa Paula were destroyed and the damage estimates cleared $20 million. At that time, it was reported to be the second worst disaster to hit the state except for the San Francisco earthquake in 1906.
Los Angeles Water System
As the Chief Engineer and General Manager of the Los Angeles Department of Water and Power, Tom Mulholland was the creator of the Los Angeles Water System. He was a self-taught engineer and a former ditch digger, yet he designed the aqueduct from the Owens Valley that brought a reliable water supply to the rapidly growing city of Los Angeles.
Ugly Politics
The situation involving the water supply strained the relationship between the City of Los Angeles and the ranchers of Owens Valley. Many ranchers felt that the city had stolen their water and in protest, a group dynamited parts of the Los Angeles Aqueduct. The termination of the city's water supply for several weeks made Mulholland realize that a reservoir was desperately needed to ensure a steady flow of water to Los Angeles.
Acquiring Land for the Project
Quietly, but legally, Mulholland began the acquisition of land for the city and the construction of the St. Francis Dam near present day Santa Clarita. He chose this particular site to locate the reservoir close to the city but south of the St. Andreas Fault Zone. This was a guarantee that a year's supply of water would be available to the city in case an earthquake should ever damage the aqueduct. At various times, the angry Owens Valley ranchers threatened to bomb the new St. Francis Dam. Security guards patrolled the construction site, but nothing developed.
The Design of the Dam and the Geology of the Site
Mulholland's proposed dam was a concrete gravity arch dam rising 185 feet high. However, he wanted to increase the holding capacity of the reservoir and his final design showed the height increased to 205 feet. Due to the political situation, Mulholland wanted to complete the dam as rapidly as possible, but he neglected to prepare a study of the geological subsurface. He never realized that the construction site was located over both an ancient earthquake fault and an enormous prehistoric mudslide.
The design did not incorporate the calculations for hydraulic uplift and the arch stresses into the basic structural design. Neither did he calculate the changes in loading due to the 11% increase inn overall height. Finally the concrete which formed the dam itself was not prepared and cured properly.
The Fatal Factor
This 20 foot increase in height was probably the most likely single fatal factor contributing to the disaster. The overstressed dam wall weakened significantly when the reservoir pool filled to within seven to ten feet of the crest only six days before the failure of the dam. On the morning of March 12th, the dam-keeper at the St. Francis reservoir reported that a new leak had developed in the dam. Muddy water was passing through the leak and this meant that the foundation was washing out from under the dam. Mulholland inspected the leak and pronounced the dam to be safe. The failure occurred about 12 hours later.
Mulholland's Rise to Power
The fateful year, 1928 saw Mulholland's engineering career soar to a majestic high and then almost immediately plunge to the darkest, deepest depression. In January of that year, Tom Mulholland rose to the peak of his career when the citizens of Los Angeles acknowledged him as the builder of their city and called for him to run for mayor. The press quoted him, "I would rather give birth to a porcupine backwards!"
The Fall
By summer of that year, he faced an indictment for murder and criminal negligence with regard to the dam failure and was summoned to appear before a Los Angeles' Coroner's Inquest. The jury found him responsible for the disaster but innocent of professional negligence and manslaughter due to his ignorance of basic engineering. When the trial ended, Mulholland entered a period of self-isolation that lasted for the rest of his life, and he resigned from his position with the Los Angeles Department of Water and Power by the end of the year.
Before the disaster, local residents considered Tom Mulholland the man most responsible for transforming Los Angeles from a small cow town to a booming metropolis. After his death only a few landmarks such as a scenic road, an elementary school in the San Fernando Valley and a water fountain now commemorate his name.
