The United States is home to many dams, with a little over 90,000 of them scattered all over the country. Although dams are supposed to be intricately built structures, these dams are still at risk of failure, and as such, they are classified by hazard potential. Saying a dam has a high hazard potential does not mean that the likelihood of the dam failing is enhanced. A dam with an increased hazard potential rating simply means that if it were to fail, the results would probably involve the direct loss of human life and significant property damage. 

Over the course of American history, hundreds of dams have failed. Numerous people have died as a result of these failures, which also caused significant property and environmental damage. The risk of fatal dam failures increases as the nation’s dams deteriorate and its population rises. In this article, you will find learn about the most devastating dam failure in the United States. We will also discuss the triggers of the dam failure and the aftermath of this tragic incident.

The Most Devastating Dam Failure in the United States

broken South Fork Dam
The worst dam failure in the United States was the Johnstown flood of 1889.

Everett Collection/Shutterstock.com

The failure of the South Fork Dam, which affected Johnstown, is currently regarded as the worst dam failure in U.S history. About eight miles to the east of Johnstown, Pennsylvania, was where the South Fork Dam, a rock and earthen dam, was built. The dam was initially constructed in 1852 with the primary objective of serving as a water source for a canal. The dam was around 918 feet in length, 72 feet in height, 10 feet in width at its crest, and 220 feet in width at its base. 

The South Fork Fishing and Hunting Club began in 1881, and between that time and 1889, the dam periodically leaked. However, mud and straw were primarily used to patch things up. Because the dam was close to a thriving community in western Pennsylvania called Johnstown, there were fears that if the dam ever did give way, the town would suffer greatly. The inhabitants of the dam were also concerned for their safety, and a concerned citizen went as far as personally inspecting the dam and sending a letter highlighting all its flaws to the club. However, his concerns were dismissed.

In May 1889, severe rains started nonstop, and it was at this point the management of the club realized the dam was in danger of giving way. However, because the people of Johnstown had experienced a lot of false alarms, they did not believe the news from the club’s management. The water gradually went over the dam, and it gave way. On Friday, May 31, 1889, around the afternoon, the water crashed down, and over 20 million tons of water carrying sand and debris flowed into the town. The water flowed into the city and flattened most buildings, killing over 2,200 people, causing the loss of 1,600 homes, and causing over $17 million in property damage. 

The flood flattened everything as the mass plowed into the city until it was stopped at the other end of the settlement by a massive stone bridge. The stone bridge was sturdy but caused its own calamity. The water backed up over the city, and as a result, caused water to flow back into the city. Then, a fire started and spread across the entire pile of properties that were already flattened by the flood.

What Caused the South Fork Dam Failure?

South Fork Fishing and Hunting Club
The South Fork Fishing and Hunting Club is believed to be the cause of the dam’s failure.

David Brossard / flickr – License

Generally, to date, the South Fork Fishing and Hunting Club is seen as the cause of the dam’s failure. The owners of the club made changes to the dam for the enjoyment of their private members.

Although the club regularly maintained the dam, they still made some risky changes. To prevent the pricey fish from eluding capture, fish screens were constructed across the spillway. The club owners also removed a small portion of the dam, lowering it to allow more than one carriage to travel the path to the clubhouse, leaving the dam only a few feet above the spillway. Rustic cottages were also erected close to the relief pipes and valves that managed the water level and spill-off from the original dam. The club never erected the drainage pipes again, preventing the reservoir from being drained. Because of all these modifications and some more, the leaks from the dam became worse.

Apart from several modifications, the club management also ignored warnings from concerned citizens of Johnstown. Daniel Morrell, one of Johnstown’s most well-known civic leaders, even had the dam inspected and wrote to the club pointing out significant faults, including the lack of a proper water outflow, but his objections were simply rejected. 

South Fork, Mineral Point, Woodvale, and East Conemaugh were utterly destroyed by the torrent of 4.8 billion gallons of water (a little over 20 million tons) and debris in just 10 minutes. The mass of wreckage was a wave 45 feet tall, over a half mile wide, and moving at 40 miles per hour by the time the roaring waters hit Johnstown.

The Aftermath of the South Fork Dam Failure

Ruins of houses after the Johnstown Flood, of May 31, 1889
The Johnstown flood of 1889 killed 2,209 people.

Everett Collection/Shutterstock.com

Due to the early summer season, only a few members were present when the dam broke on May 31, 1889. They left immediately after the incident, and the club members kept quiet about the tragedy. A small group of outraged flood survivors approached the club and broke into several of the buildings, shattering windows and trashing furniture, although there was minimal structural damage. The club donated blankets to the survivors of the flood in the immediate aftermath of the disaster, a few club members participated in relief committees, and many of the club members made donations to the relief fund, some of which were as large as $10,000.

Hundreds of journalists flocked to the city to cover the deadliest natural disaster in American history as the floods started to recede. They had a tally that showed that the flood had killed 2,209 people and destroyed four acres of downtown Johnstown. The city was gradually rebuilt in the days and months that followed. More relief came from people across the country who sent food, clothes, and money, and also from the recently formed American Red Cross that arrived to provide medical assistance, emergency shelter, and supplies. 

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