On the 12th of March, 1928, just before midnight, the St Francis Dam in Los Angeles County,

California, failed catastrophically.

The dam, built just a few years before, had been holding back around 47 million cubic

meters (or 12.4 billion gallons) of water.

Now, as the concrete of the dam crumbled, this water swept down the Santa Clarita river

valley in a gargantuan wave, destroying everything in its path.

The collapse of the dam would turn out to be one of the worst civil engineering disasters

in American history.

The city of Los Angeles grew rapidly during the first half of the 20th Century, with its

population rising from 100,000 in 1900 to more than half a million in 1920.

Water had been in short supply in the area for decades, and this population boom only

made matters worse.

In charge of addressing this chronic water shortage was William Mulholland – a brilliant

self-taught engineer.

Having started out as a ditch tender, he had studied hard and worked his way up to become

the head of the Los Angeles Bureau of Waterworks and Supplies.

Mulholland’s first solution was to build a massive aqueduct – a series of pipes and

reservoirs that could transport huge amounts of water from the Owens River in the Sierra

Nevada Mountains directly to the burgeoning city of Los Angeles.

The project, completed in 1913, was a stunning example of engineering – the aqueduct carried

water 375 kilometres (or 233 miles) using gravity alone, ensuring an ongoing supply

of fresh water for the city of Los Angeles.

While the aqueduct was great news for residents of Los Angeles, it certainly did not find

favour with those living and working in the area that it took water from.

With so much water diverted out of the Owens River, farmers on its banks could no longer

properly irrigate their fields, and the economy of the region was devastated.

Feelings ran so high, in fact, that there were frequent attacks on the aqueduct.

Furious residents would use dynamite to blow up sections of pipeline, or else covertly

open sluice gates to disrupt the flow of water.

While certainly effective at bringing water to the city, the aqueduct was extremely controversial.

Mulholland’s work, however, was not complete.

A more reliable water source was needed to protect the growing city in times of drought…

or to provide a backup should the aqueduct ever be taken out of action.

Mulholland decided that a giant reservoir should be constructed – and in 1924 work

began on a project to dam a section of the San Francisquito Canyon in order to do just

that.

Construction lasted two years, with the dam finally opened in 1926.

The finished dam was actually three meters (or ten feet) taller than had originally been

planned – a change which massively increased the capacity of the reservoir behind the dam,

but also necessitated the construction of an extra wing to the structure.

The completed dam was as an imposing stepped concrete wall, supplemented by a long, low

dyke on one side, which turned the canyon into a reservoir big enough to see Los Angeles

through even the driest of dry spells.

Very early on in its life some cracks appeared in the dam.

This wasn’t abnormal for a dam of the size and design of the St Francis dam, and thus

didn’t cause any great alarm…

at least not until 1928.

It was in this year, with the reservoir almost completely full, that new cracks were observed

in the structure, along with the seepage of muddy water – something which could indicate

that the foundations of the dam were being eroded away.

Mulholland himself was called to inspect the dam on the 12th of March, 1928, and came away

with the impression that corrective action was required…

but not urgently.

It was mere hours after he made this assessment, however, that the dam gave way.

The failure of the dam was swift and violent – so violent, in fact, that nobody who witnessed

it survived to tell the tale.

Within just a few minutes the concrete of the dam broke into several pieces, with huge

chunks blasted downriver by the pressure of the water behind them.

Only a single narrow segment of the dam remained standing and intact.

As the dam gave way, a wave the height of a thirteen-storey building was unleashed,

and flooded down the Santa Clarita River Valley, annihilating almost everything in its path.

One of the first structures to be destroyed by the flood was the cottage of the dam keeper,

which was so thoroughly swept away that neither his body nor the body of his young son were

ever found.

A little further downriver stood one of several hydroelectric power stations situated in the

valley.

This was completely destroyed, with the loss of all but three of the workers employed there.

The housing and various support structures for power plant workers were also destroyed,

with whole families killed in the space of just minutes.

As the wave continued down the river valley, it struck one small town after another.

Houses were flattened, buildings picked up and swept away by the force of the flood.

The water became a torrent of debris, including trees, motor vehicles, the remains of pulverised

buildings… and also people.

In many cases there was no warning for the residents of the towns hit by the flood.

People were swept from their beds and carried for mile upon mile in a seething torrent of

water and debris.

Many drowned, but many more were killed when they were struck by objects carried by the

flood.

Some people were lucky enough to receive a warning before the flood wave reached them.

Telephone operators, once aware of the disaster, spent hours systematically calling the homes

of people in low-lying towns, warning them to flee to higher ground.

Meanwhile two highway patrol officers – Thornton Baker and Stanley Edwards – rode motorcycles

back and forth through Santa Clara with their sirens on, ordering anyone they encountered

to evacuate.

Thanks to these interventions, hundreds of people were able to make a last-minute dash

to higher ground.

Though they lost everything in the flood, they at least escaped with their lives.

At around 5:30am the wave reached the coast, where it emptied out its cargo of debris,

dead bodies, and a few dogged survivors into the Pacific Ocean.

Hundreds of victims were never recovered, while some bodies were found as far south

as the Mexican border.

Over the course of five-and-a-half hours the wave had carved out a path of absolute destruction

along the course of the river valley.

At least 431 people – and probably many more – were dead.

Thousands of homes and businesses were destroyed, and several communities had been all but wiped

from the map.

In the immediate aftermath an explanation was sought.

Because of attacks on the Los Angeles aqueduct in previous years, some suspected that the

dam had been sabotaged… but multiple inquiries found no evidence of this.

Instead it was determined at the time that the foundations of the dam had been defective.

Mulholland, devastated by the disaster, accepted full responsibility for it, and retired in

the same year, stating, “Don't blame anybody else, you just fasten it on me.

If there is an error of human judgment, I was the human.”

He was, however, not charged with any crime.

Almost every inquiry into the disaster concluded that he had made decisions that were correct

and appropriate based on the knowledge that was available at the time.

In the decades since the collapse of the St Francis dam our understanding of what went

wrong has evolved significantly.

We now understand in much greater detail how the geology of the canyon contributed to the

failure by allowing water to seep in and saturate the hillside into which the dam was anchored.

We also understand the phenomenon of hydraulic uplift, whereby the presence of water underneath

a structure like a dam can lift it up, contributing to a catastrophic collapse.

From a modern perspective, numerous mistakes were made in the siting, construction and

management of the dam.

But our understanding of these issues is the product of many years of dedicated study,

experimentation and experience.

When Mulholland supervised the building of the St Francis Dam, all of this knowledge

was yet to be garnered.

He conformed to the standards of the time… and it was only when the project failed in

such a devastating fashion that it was realised that these standards were insufficient.

Many changes took place as a result of the collapse.

Dams across the country were inspected, and several were reinforced.

The regulation of the construction of dams was stepped up.

It was made mandatory to consult a dedicated geologist on any large-scale construction

project, and – perhaps most importantly of all – the Board of Registration for Civil

Engineers was created, and engineers were required to be licenced.

The idea of a self-taught engineer became, very quickly, a thing of the past.

The tall, tombstone-like piece of the dam which survived the collapse stood for just

over a year before it was demolished to prevent it becoming a morbid tourist attraction.

Evidence of the disaster is still to be found to this day, however, all along the route

that the flood wave took that night in 1928.

Huge chunks of rubble remain at the site of the dam.

Memorials are sited up and down the river valley, and the event is an indelible part

of the history of the region.

Though almost a century in the past, the failure of the St Francis Dam is still remembered,

and still shapes the modern world.