The Failure of the St. Francis Dam Group #1

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The Failure of the St. Francis Dam

Group #1

Susan Rambridge

Marlborough High School


March 3, 2014

On March 12, 1928 the St. Francis Dam cracked, causing a flood that killed 600 and flattened the city of Santa Paula. Dams have been built for many years to block bodies of water to build cities, to create storage for water, and to produce hydroelectric power. The growing city of LA needed water and the St. Francis dam was built to provide storage for the LA aqueduct (Civil engineering disasters).

LA was a city in the middle of the dessert. An aqueduct, which is a conduit or artificial channel for conducting water from a distance, was built. If a drought was to occur, LA needed a back-up to get additional water. The St. Francis dam was created to make an artificial reservoir to store a large quantity of water for LA families (Scott. 2012). The dam was also used to funnel water to power stations nearby. The stations had generators that used hydropower to create electricity for cities close by (St. Francis Dam).

The St. Francis dam was built under the supervision of William Mulholland, an engineer and general manager of LA department of Water and power (Saint Francis Dam Disaster). He designed the dam to be an arch/gravity design, which had some pros and cons. An arch design dam is where the hydrostatic forces that build up are absorbed by the curved arch and these are distributed uniformly to the foundations and abutments. Arch dams are normally used for tall narrow spaces because they allow for a reduction in wall thickness. A gravity design dam is only slightly curved and its stability is based on inherit strength only. Gravity dams can be used for any topography but normally support a smaller reservoir. To try and get best of both William Mulholland combined the designs. The final design was a slightly curved, concrete dam facing upstream. The dam was to be 175ft high by 608ft wide. Before construction 10ft was added to the height of the dam. Then halfway through construction another 10ft was added. From 1924 to 1926 5,000 men worked on the construction of the dam. When finished the St. Francis dam was 195ft high and, because of the new height a wing dike was added along the top of the ridge adjacent to the dam in order to contain the enlarged reservoir. The foundation was thought to be very sturdy and strong, but it was later discovered that the foundation was anything but that (Scott, 2012). The dam could store up to 12.4 billion gallons of water and since it was acting as a storage point for the LA aqueduct, it was built 40 miles north of Los Angeles near Santa Clarita (Nicholos, 2002).

After the dam was constructed it operated for two years, then on the morning of March 12, 1928 an inspector noticed muddy water at the foot of the dam. It was inspected thoroughly and was thought to be water from one of the power stations and to be no threat (Fact Index ). Multiple people who drove along the east abutment side road noticed that the road had dropped about 12in. This was the prelude to the whole dam collapsing (Nicholos, 2002) and that night a little before midnight the dam cracked, sending a flood wave about 125ft high down the valleys towards the ocean 54 miles away. When it reached the ocean at 5:30 a.m., the flood was almost two miles wide, traveling at a speed of 5 miles per hour ("1928 St. Francis Dam: Timeline and Flyover: Multimedia: Ventura County Star”).The floodwaters destroyed everything in its path; livestock, bridges, towns, structures, and the famous orchards of the area. Santa Paula, Castaic Junction, Fillmore, Bardsdale and parts of present-day Valencia and Newhall were flooded (Scott, 2012).

The flooding had a great impact on the communities downstream of the dam. Most cities were completely leveled. The wave swept away people in its path killing 600 (Saint Francis Dam Disaster). It would have been more but some brave police officers, who were warned of the dam cracking by a motorcyclist who passed by it on a road, risked their own lives to go around and tell families to evacuate. There was still a fairly large death toll because most people were sleeping. The flood caused debris and bodies to be swept into the Pacific Ocean and much of that was fished out of the ocean weeks later. Other debris found were parts of the dam that were found up to a half mile downstream (Saint Francis Dam Disaster). Many death and injury claims were made as well as the cost of homes and buildings destroyed, made the total cost of the disaster about 14 million dollars (Impact of St. Francis Dam).

Several reasons were found to have caused the failure. Later investigations lead to find that the east abutment was built on land that was unstable. Also, the dam was filled to full capacity just days before it failed, so the dam was under more stress than normal. William Mulholland designed the dam then added 20 feet by the time it was finished, without changing the strength of the dam. So the Safety factor was a 1, the Safety Factor is calculated by dividing the actual structural strength by the minimum structural strength required, when it should have been at least a 4 (Scott, 2012).

The St. Francis Dam failed due to multiple factors. The height additions flawed the safety standard. Also the dam just met full capacity before it failed and the foundation was not sound. This disaster resulted in the destruction of multiple cities and costing 600 lives. Many dams are built for multiple reasons, unfortunately the St. Francis dam failed.


1928 St. Francis Dam: Timeline and Flyover: Multimedia: Ventura County Star. (n.d.). Retrieved from

Retrieved from

Civil Engineering Disasters: The St. Francis Dam Flooding. (n.d.). Retrieved from

Nichols, J. (2002). St. Francis Dam disaster. Chicago, Ill: Arcadia Pub.

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

Scott, W. (2012, March 13). Engineering Disasters: the St Francis Dam Failure. Retrieved from | St. Francis Dam Disaster: Death & Disability Claims & Claimants. (n.d.). Retrieved from

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

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

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