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St. Francis Dam

The St. Francis Dam was a concrete arched gravity dam built in 1924-1926 by William Mulholland, engineer for the Los Angeles Department of Water and Power, as a large reservoir near the City of Los Angeles. Minutes before midnight on March 12, 1928, the dam catastrophically failed (collapsed) and over 400 people were killed by the resulting flood.

The need for the dam

William Mulholland was a self-taught
civil engineer, a native of Ireland. He designed and built what was then the longest aqueduct in the world, taking water from Owens Valley and bringing it to Los Angeles, some 235 miles away. When the aqueduct was completed in 1913 there was a surplus of water, but Los Angeles grew at an unbelievable rate and by 1920 there was a need for even more water. Several small reservoirs were built in 1921 to supply the city in the event of a drought or damage to the aqueduct, but it was clear that a major reservoir was needed.

Mulholland had first considered the San Francisquito Canyon, about 30 miles north of Los Angeles, as a potential damsite in 1911. The Aqueduct ran conveniently along the canyon and two generating stations were located there to use aqueduct water to generate electricity for Los Angeles. It seemed the perfect location since the reservoir would not only protect against drought, but if the aqueduct were to be damaged by an earthquake (or sabotage) there would be enough water in the reservoir to supply Los Angeles until repairs could be made.

Construction begins

Today geologists know that the type of rock found in the San Francisquito Canyon is unsuitable for supporting a dam and a reservoir. Unfortunately in the 1920s geology was a relatively new science and even two of the worlds leading geologists at the time, John C. Branner of Stanford University and Carl E. Grunsky, found no fault with the San Francisquito rock.

Also, the dam was built squarely over the San Francisquito earthquake fault, although this fault has long since been dead.

In 1924 construction began on the St. Francis Dam, which was given an Anglicized version of the name of the creekbed on which it rested. The project began quietly so that the farmers dependent on the water of the San Francisquito Creek wouldn't notice the dam and try to stop the construction.

Major Alterations

The St. Francis Dam was designed to be 175 feet tall and to hold back a reservoir of 30,000 acre-feet. An acre-foot is the amount of water that will cover an area of one square acre at a depth of one foot, or about 325,851 gallons.

Right after construction began in 1924, Mulholland decided to raise the dam 10 feet and increase the capacity of the reservoir to 32,000 acre-feet. Since little construction had been done some minor changes were made in the design to accommodate the change. However, in July of 1925, when the dam was about halfway completed, Mulholland again decided to raise the dam another 10 feet to a total height of 195 feet. A "wing dyke" had to be constructed on the western side of the dam to keep water from spilling over a low ridge when the reservoir filled. The new capacity was 38,170 acre-feet.

Gravity dams, like the St. Francis Dam was and the Hoover Dam is today, use their weight to resist the water pressure exerted on them. The St. Francis Dam was increased in height from the designed 175 feet to 195 feet at completion, without any substantial widening of the dam’s base. Today this is a big no-no but little was said about the changes in 1925.

Sabotage

In 1927 a few people in Owens Valley who were fighting the California Water War dynamited the Los Angeles Aqueduct several times. The St. Francis Dam and Reservoir saved Los Angeles from a severe water shortage and water from the reservoir also generated electricity. Mulholland called the dam "providential."

During the height of the Water War there was a threat made against the St. Francis Dam and an anonymous informant pleaded to the Los Angeles police to "get some officers up there quick." Fortunately no attempt was made to dynamite the dam.

Prelude to failure

Several cracks appeared in the dam throughout 1926 and 1927. Some began to leak. Mulholland inspected these cracks and found them to be of no consequence. All concrete dams form cracks over time.

On March 7, 1928, the St. Francis Reservoir was completely filled for the first time. New leaks were discovered by the damkeeper, Tony Harnischfeger, but Mulholland was convinced they were relatively minor.

Another factor in the failure could have been the construction of a new road along the east abutment, which was over the ancient landslide. Blasting with dynamite was done right up until March 8, 1928, and much of it right next to the unstable abutment. It is unknown if the blasting could have loosened the rock or not.

On the morning of March 12 damkeeper Tony Harnischfeger discovered a new leak and he was worried that it was undermining the dam. Mulholland, his son Perry, and his assistant Harvey van Norman came to the dam immediately to investigate. When Perry said that the leak looked serious, his father scoffed and said "That's typical of concrete dams." The dam was declared safe and Mulholland returned home.

Failure

The dam finally crumbled at 11:57 pm on March 12, 1928, scarcely 12 hours after Mulholland had inspected it. There were no surviving eyewitnesses to the failure, but one man on the road about a half mile away from the dam recalls feeling a strange shaking of the ground and the sound of "crashing, falling blocks." The shaking he felt was no earthquake (seismographs recorded no significant earth movements) but rather the tumble of incredibly heavy pieces of concrete that were falling off the dam.

Exactly how and why the dam failed has never been completely determined. Engineer and geologist J. David Rogers has published the most comprehensive account of the dam's failure, which he says was caused by uplift, the instability of the paleomegalandslide, and Mulholland's unwise raising of the dam's height.

Tony Harnischfeger was probably the first to die in the floodwave, which was about 125 feet high when it hit his little cottage in the San Francisquito Canyon. His body was never recovered.

The disaster

Twelve billion gallons of water surged down the San Francisquito Canyon, crushing the heavy concrete walls of a hydroelectric power plant sweeping away everything else in its path. The flood continued down the San Francisquito then into the Santa Clara River bed. The towns of Castaic Junction in Los Angeles County and Fillmore, Bardsdale, and Santa Paula in Ventura County were hit especially hard.

Brave telephone operators stayed at their posts and called home after home warning people to get to high ground. Perhaps the most famous story of the disaster is of the motorcycle policemen that went up and down the streets of Fillmore and Santa Paula with their sirens wailing until the rising floodwaters forced them to retreat.

The aftermath

The exact number of dead remains unknown to this day. The official count made in August of 1928 stood at 385. However more bodies were discovered every few years until the 1950's, and the remains of another victim were found deep underground near Newhall in 1992. It is generally accepted that over 400 and less than 500 died in the flood.

William Mulholland shouldered all the blame willingly. He was so easily made a scapegoat that the initial investigations weren't as thorough as they might have been. Although Mulholland accepted the blame, he hinted during his trial for manslaughter that he felt the dam was sabotaged.

The dam was not rebuilt. Several large pieces of concrete were not swept away by the waters, including the center section of the dam which remained standing upright. After the death of a young man who fell from a large piece of concrete while exploring the ruins two months after the failure, the remains of the dam were dynamited and jackhammered into oblivion.

Today all that remain are a few weathered chunks of gray concrete and the rusted remains of the handrails that lined the top of the dam. The ruins are very easy to see from the San Francisquito Canyon Road, about five miles north of the city of Newhall.

More information; books and websites

Man-Made Disaster, Charles F. Outland's excellent study of the dam and the ensuing flood, though rather old (first published in 1963), is the only widely published comprehensive work about the dam, the failure, and the disaster that followed. It is a first-rate bit of "from scratch" research, and it is becoming quite rare and difficult to find.

The St. Francis Dam Disaster Revisited, a collection of articles about the dam with contributions from Catharine Mulholland (William Mulholland's granddaughter) and Dr. J. David Rogers, is the only other book on the St. Francis Dam in print today.

External links