Excluding the floods caused by hurricanes, the deadliest flood in the US occurred on May 31, 1889 when the South Fork Dam burst.

History of Johnstown Pennsylvania

Located in a river valley in the Allegheny Mountains approximately 65 miles east of Pittsburg, Johnstown was founded in 1794. It is located on a flood plain at the junction of the Little Conemaugh and Stonycreek rivers which form the Conemaugh River.

In 1834, the Pennsylvania Mainline Canal was built and the town prospered with the arrival of the Pennsylvania Railroad in 1852 and the subsequent establishment of the Cambria Iron Company.

History of the South Fork Dam

The South Fork Dam was built by the Commonwealth of Pennsylvania between 1838 and 1852 as a reservoir for the canal basin in Johnstown.

The dam is located 14 miles upstream from Johnstown. The Comenaugh River runs through the heart of Johnstown and it had been made narrower in order to build more structures on it banks. The river was susceptible to flooding due to it’s location on a flood plain and it’s forced narrowing.

The Commonwealth of Pennsylvania sold the dam and canal to the Pennsylvania Railroad in 1857. With the arrival of rail service in 1852, the use of the canal for delivery of goods took a downturn. The South Fork Dam was abandoned and allowed to go into a state of disrepair. In 1862, part of the culvert gave way but was never repaired.

In 1879, a group of businessmen formed a company and called it the South Fork Hunting and Fishing Club. They purchased the dam with the intention of building a summer resort on Lake Comenaugh for wealthy Pittsburg families. Plans included lowering the dam in order to build a road on top and raising the level of the lake. The club continued to make alterations to the dam and in the end, the lake was 450 feet higher than Johnstown.

The Breaking of the South Fork Dam

A violent storm formed over the Midwest and hit Johnstown on May 30th 1889. The rains were extremely heavy and it was estimated that six to ten had fallen in the 24 hours prior to the dam bursting.

On the eve of May 31st, flooding began in the creeks and rivers which eventually caused the Conemaugh River to rise to a dangerous level. Trees and other debris were floating downstream in torrential water, causing the washout of railway and telegraph lines.

Lake Conemaugh had risen over two feet overnight and by 7:00am; the water was less than three feet from the top of South Fork Dam. The dam spillway screens became clogged with heavy debris from the lake. The water was quickly rising and 3 hours later, the water was less than 12 inches from the top of the dam.

Workers tried to pull the debris away from the spillway screens and dug trenches on the hillside in order to divert the water away from the dam. The dam was bowing in the middle and workmen threw more earth on it in hope of adding more strength. It was too late.

On 3:10pm May 31st 1889, the South Fork Dam gave way and 20 million tons of water spilled over the dam and headed to the valley. With no warning, Johnstown was hit with a rushing wall of water and debris traveling at 40 miles per hour. In some places the water was as deep as 60 feet.

In the end, over 2,200 people lost their lives and the damage was estimated to be $17 million USD. Four square miles of downtown Johnstown were destroyed and clean-up didn’t finish until five years later. In the aftermath, there were masses of fallen trees, railway cars, wires from the steel factory and houses reduced to pieces of timber.

This was the first major disaster faced by the newly-formed American Red Cross. Aid came from 18 countries across the globe.

The Cause of the South Fork Dam Break

• Although the heavy rainfall was the cause of the big break, if the dam had been properly constructed and maintained, it could have been averted.
• The iron discharge pipes that allowed the controlled release of water were removed and sold for scrap. If there had been sufficient spillways, the water level of the lake could have been better controlled.
• The new parts of the dam were constructed of stone, mud and straw. It was not as strong as the original structure. As a result, the rising water started to erode the unstable embankment.

Lawsuits against the South Fork Hunting and Fishing Club were overruled because this disaster was considered” An Act of God”.

Sources:

• Johnstown Flood National Memorial
• Wikipedia
• Johnstown PA History