World Facts

The Worst Floods in US History

Johnstown Flood, St. Francis Dam Failure, and Ohio River Flood are among the worst floods in US history.

Despite being a global superpower, the United States has had the unfortunate distinction of having one of the highest numbers of natural disasters experienced by any country. Almost annually, the United States is hit by tornadoes, hurricanes, and floods. Some of the worst floods have led to a great loss of life as well as property destruction.

The Worst Floods in US History

Johnstown Flood

The Johnstown Flood of 1889 was one of the deadliest natural disasters experienced in the United States and was the worst flood in US history. An estimated 2,209 people lost their lives due to the Johnstown Flood, making it America’s deadliest flood. The flood which is also known as the Great Flood of 1889, took place on May 31st, 1889 and was caused by the collapse of the South Fork Dam. The dam which was constructed on the Little Conemaugh River could not contain the tremendous pressure exerted by rising water levels of the reservoir. To compound the problem, the dam’s spillways were clogged by debris. The river’s upstream had experienced heavy rainfall, with as much as 10 inches of rain being collected in the region. Existing communication channels were slow and therefore news of the impending catastrophe took long to reach people living downstream. The towns of Johnstown and South Fork were destroyed by the floods, leading to an estimated $453 million in property damage.

St. Francis Dam Failure

St. Francis Dam which impounded the San Francisquito Creek and the Los Angeles Aqueduct was situated in Los Angeles County, California. The dam was opened in 1926 after taking two years of construction. However, the dam collapsed on March 12th, 1928 leading to the worst flooding experienced in California’s history. Several months before the dam’s collapse, numerous cracks had appeared on its surface. On the fateful day, more than 12.4 billion gallons of water gushed out of the collapsed dam, transporting fragments of the dam downstream. One fragment weighing about 10,000 tons was washed 0.75 miles downstream. About 431 people lost their lives in the floods, the second-deadliest disaster in the history of California.

Ohio River Flood

The Ohio River Flood was the third deadliest flood in US history, causing the deaths of 385 people. The Ohio River had a history of floods, but events witnessed in 1937 saw the river’s water levels rise to unprecedented levels. By the start of the year, heavy rainfall in the river upstream caused the river to swell to a worrying level, and by January 18th, 1937, flood warnings had been issued in several regions. The heavy rains persisted throughout January and by January 26th, water levels in Cincinnati had reached a record 80 feet. By January 27th, an estimated 70% of the city of Louisville was flooded. The Ohio River Flood caused as much as $8.7 billion in property damage.

Flood Management

Most of the deadliest floods in US history were attributed to the collapse of dams brought about by poor engineering practices. As a result, the US government invested in proper dam engineering to construct strong and durable dams. An excellent example of a dam which has stood the test of time is Hoover Dam which has been a testament to proper dam engineering for about a century.

The Worst Floods in US History

RankFlood NameState(s)YearCasualties
1Johnston Pennsylvania18892209
2St. Francis Dam FailureCalifornia1928431
3Ohio River Flood of 1937Pennsylvania, Ohio, West Virginia, Kentucky, Indiana, Illinois1937385
4Great Dayton FloodOhio1913360
5Great Mississippi Flood of 1927Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Missouri, Tennessee, Texas, Oklahoma, Kansas1927246
6Black Hills FloodSouth Dakota1972238
7Los Angeles Flood of 1938California1938115
8Columbus, Ohio flood on March 25, 1913Ohio191390
9Failure of Laurel Run Dam and flash floodingPennsylvania197780
10Austin Dam FailureTexas191178

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