The Catastrophic Break Through

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The Catastrophic Break Through

By Riley Heath

On March 12th, 1928 the St. Francis Dam cracked causing a flood that killed up to 600 people and flattened the city of Santa Paula. The St. Francis Dam was designed to create a reservoir as a storage point of the L.A. Aqueduct. The rapidly-expanding city demanded a reservoir to provide a larger water supply. Alongside the demand for more water, the two generating stations used water from the aqueduct to provide another power source for L.A.

The construction of the St. Francis Dam lasted from 1924 to 1926. The Dam was built in the Santa Clara River Valley near southern California. It was only 40 miles northwest of L.A. The chief architect, William Mulholland, was devastated when the dam failed. Not just because of the great loss of life and land, but because “the incident marked the end of a distinguished career.” (Marilyn A. Dyrud, 2014) It was Mulholland who made the decision to build the dam in the canyon. He didn’t pay much attention to the support of the foundation; which is the canyon; for which the dam would be built. It is this carelessness made by Mulholland that was a main factor in the failure.

What Mulholland more or less ignored was the geology of the site, a critical mistake, since the dam, an arch-gravity design, would anchor into the canyon walls. At that time, however, geological opinion was not required for dam sites. Had it been mandatory, the dam would never have been built on what was clearly unstable land.”

The ‘unstable land’ mentioned in the article cited above, was a fatal mistake made by Mulholland’s decision to overlook it.

The St. Francis Dam created a reservoir that contained ample water in the event of a drought or aqueduct damage caused by an earthquake or sabotage. The design of the dam was a concrete gravity-arch dam.

An arch-gravity dam or arched dam is a dam with the characteristics of both an arch dam and a gravity dam. It is a dam that curves upstream in a narrowing curve that directs most of the water against the canyon rock walls, providing the force to compress the dam.”

This design combines the strengths of two common dam forms and is considered a compromise between the two. The dam was 195 feet high, 608 feet long and had a capacity of over 38,000 acre-feet. It’s impound is located in San Francisquito Creek.

The construction of the St. Francis Dam began in 1924 keeping in mind the main purpose of providing storage for the Los Angeles-Owens River Aqueduct. This aqueduct would “provide a reliable source of water” for the ever-growing city of Los Angeles. The dam was final completed in the year 1926. Later, for the first time since construction, the dam was filling to its capacity in 1928. After a drought hit, there was a need for more reservoir capacity. “Mulholland raised the dam from 175 to 195 feet without demanding reinforcement. The reservoir began filling in 1926. Water rose to 165 feet in the first three months.” (John H. Lienhard, 2014) Then, just before midnight on March 12th, 1928, the dam broke.

There are multiple factors that contributed to the failure of the St. Francis Dam, but there are a few that made a larger impact. The dam’s base for example. The dam’s base was not as thick as it should have been. Now take that, and the ‘unstable land’ that it was built on, that makes it really susceptible to cracking. Another contributing factor to its demise was the lack of reinforcement. When the drought hit, they need to make the dam big enough to hold back the new amount of water. Mulholland rectified this by adding height to the dam, there-by increasing the total capacity. This could have worked if he had reinforced the new addition to the dam as well, but he did not. “As work began in 1924, a drought sent people clamoring for even more reservoir capacity. Mulholland raised the dam from 175 to 195 feet without demanding reinforcement.” (John H. Lienhard, 2014)

The results of the wave were tremendous. It went on a rampage along the Santa Clara River, where many people resided. This monstrous rush of water killed over five-hundred people and left thousands without a home. “along the way, it picked up trees, boulders, houses, livestock and people.” (St. Francis Dam disaster: A tale..., 2014) The water rushed along for miles, leaving demolished homes in its wake. “ It snuck up on unsuspecting families, farmers, ranchers and laborers in their sleep during its 54-mile rampage along the Santa Clara River to the sea.” (Shannon Master, 2014)

The St. Francis Dam was built to create a reservoir, but instead it flattened the towns. Mulholland, the chief architect is to blame for overlooking the geological fact of unstable ground and the lack of reinforcement. The result was over five-hundred souls lost and thousands more without a home.


U. (n.d.). Arch-gravity dam. Retrieved April 1, 2014,

Department of Power and Water (n.d.). History of the LA Aqueduct. Retrieved from

Dyrud, M. A. (n.d.). Retrieved April 1, 2014,

Lienhard, J. H. (n.d.). No. 1325: The Day the Dam Broke. Retrieved from

Mason, D. (n.d.). Ojai Valley Museum History Timeline. Retrieved from

Master, S. (n.d.). St. Francis Dam disaster: Mulholland?s tragic mistake. Retrieved from

U. K. (n.d.). St. Francis Dam. Retrieved from

Ventura Country Star (n.d.). St. Francis Dam disaster: A tale of failure, tragedy and heroism » Ventura County Star. Retrieved from

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