9 worst floods in the U.S. and how they changed history

These storm surges, river and flash floods led to the largest loss of human life

Updated March 13, 2024

Reviewed By Ross Martin

Table of contents:

Types of floods
Worst coastal floods
Worst river floods
Worst flash floods
Preparing for floods

There’s nothing scarier than images of waters rising, cutting off roadways and destroying homes. And if you feel like you see these stories happening more frequently, you’re right.

Over the past fifty years, we have experienced a 20% increase in the heaviest downpours as a result of global climate change. We’ve also seen an increase in hurricanes specifically, which often cause flooding. It is estimated that our nation’s floodplains – the areas considered in threat of floods – will increase by 40 to 45% in the next century^[1].

Floods can cause extreme devastation in loss of life, loss of property and financial losses. And while modern storms tend to cause more costly damage (as there are more costly things to destroy), some of the deadliest storms happened in prior centuries when people didn't have the technology to escape them.

Let’s look at some of the deadliest floods that have occurred in the United States and some of the massive changes they brought.

Types of floods

There are three main types of floods:

Coastal floods: Also known as storm surges, these usually occur when a high tide coincides with an intense storm, such as a hurricane, or a tsunami, forcing large amounts of water onshore.
River floods: Also known as fluvial floods, these occur when the water level of a lake or river overflows into surrounding lands. These are often caused by excessive rain or snowmelt.
Flash floods: Also known as pluvial floods, these occur when extreme precipitation causes a flood independent of a body of water. These can happen anywhere, including in urban areas when the drainage system or dam is overwhelmed.

We’re dividing the worst floods into the top three from each type of flood. We’re using the number of lives lost for the criteria for which floods were the most devastating.

Worst coastal floods

Primarily due to hurricanes, these are the worst storm surges to ever affect the United States.

1. Galveston Island Storm of 1900

Lives lost: 8,000 people

Property damage: $1.25 billion

On September 8, 1900, a hurricane hit Galveston Island off the coast of Texas. The barrier island was at the time a thriving port city and business center with a population of around 37,000. The storm in 1900 led to a 15-foot storm surge that flooded the city and cut it off from the mainland. When rescuers were able to reach the island two days later, they found homes and businesses destroyed and thousands dead. The ultimate death toll is not truly known, but it is estimated that 8,000 people lost their lives, 10,000 more were left homeless and $1.25 billion (adjusted for inflation) in damages were done. It is regarded as the deadliest natural disaster in U.S. history.^[2]

2. Sea Islands Hurricane

Lives lost: 2,000 people

Property damage: $23 million

In August of 1893, a Category 3 hurricane formed off the Atlantic coast. Its storm surge devastated the Sea Islands and the peninsulas that line the Georgia and South Carolina coastline. Around 2,000 people are believed to have drowned during the event. Nearly every building on the islands was damaged beyond repair, and thousands were left homeless. Rebuilding was a 10-month-long relief effort, and cost around $23 million adjusted for inflation.^[3]

3. Hurricane Katrina

Lives lost: 1,833 people

Property damage: $108 billion

On August 29, 2005, Hurricane Katrina devastated the city of New Orleans. Katrina would become the costliest hurricane ever to hit the United States, causing $108 billion in damages and killing 1,833 people.^[4] A number of factors worked together to create this tragedy. New Orleans, once a city at sea level, had over time sunk below sea level due to its swampy foundations. The parts of the city most prone to flooding were occupied by many people living below the poverty line, who weren’t able to easily evacuate. The huge storm surge destroyed the city’s levee system and left 20% of the city underwater. It took over a month for all of the flood waters to be pumped out of the city and the population has still not returned to its pre-2005 numbers.^[5]

Worst river floods

Primarily caused by heavy rains overwhelming inland infrastructures and dams, these are the deadliest river floods in U.S. history.

4. Johnstown Flood

Lives lost: 2,209

Property damage: $17 million

On May 31, 1889, the South Fork Dam on the Little Conemaugh River upstream from the town of Johnstown, Pennsylvania burst after unprecedented rainfall. Because of some confusion and previous false alarms, the people of the town were not warned of the impending failure until it was too late to evacuate. The failure of the dam meant that some 3.8 billion gallons of water flooded into the town, bringing trees, houses and even 170,000-pound locomotives with it. The flood killed 2,209 people, caused $17 million in property damage and destroyed four square miles of Johnstown.^[6]

5. Great Ohio Flood

Lives lost: 428 people

Property damage: $3 billion

In March of 1913, one of the most severe weather events to hit the state of Ohio occurred. This one could arguably be categorized as both a river flood and a flash flood as the two worked together in a one-two punch that affected much of the state. Snowmelt thawed earlier in the season than usual which led to raised water levels in most of the state’s rivers. Then, in March it began to rain, and it didn’t stop. In a matter of days, the region received the amount of rain it normally gets in a three-month period. The city of Dayton had flood waters reaching 20 feet high. Some were able to evacuate, but not all. In all, 428 people lost their lives, 20,000 homes were destroyed and damages averaged $3 billion adjusted for inflation.^[7]

6. The Great Mississippi River Flood

Lives lost: 250 people

Property damage: $5 billion

In the spring of 1927, the greatest river flood on record occurred affecting states all along the Mississippi River system from Illinois to Louisiana. It happened because of excessive rainfall, which then caused a cascade effect that led to the failure of the entire levee system used to control the massive river. The river swelled and flooded surrounding settlements killing 250 people, displacing thousands and leaving an estimated 750,000 people without food or water.^[8] Property damage was estimated at $5 billion when adjusted for inflation. Economic losses were equal to about one-third of the federal budget at the time.^[9]

The Great Migration

The Mississippi flood also had political and social changes. Black Americans were among those heavily affected and also received very different treatment in terms of relief efforts. This both led to many switching political parties and also spurred on the Great Migration of Black southerners to northern cities.

Worst flash floods

Caused by any combination of factors that leads to a very sudden increase in water, not necessarily stemming from a river or lake, these are the deadliest flash floods in U.S. history.

7. Lake Okeechobee Flood

Lives lost: 2,500 people

Property damage: $1.7 billion

In September of 1928, a hurricane hit South Florida that would become the fourth deadliest hurricane to ever hit the United States. This was in part because heavy rains overwhelmed the dam holding back the water of Lake Okeechobee and flooded the surrounding farm communities. 2,500 people would ultimately lose their lives. This combined with the start of the Great Depression meant it was very difficult for this area of South Florida to recover. By 1930, Florida had lost 1.5 million people in their total population.^[10]

8. St. Francis Dam failure

Lives lost: 432 people

Property damage: $7 million

Constructed in 1926, the St. Francis Dam was a concrete gravity dam built to provide a storage reservoir for the city of Los Angeles. The dam’s architect William Mulholland was a self-taught engineer who is believed to have made some grave errors that led to its demise. On May 12, 1928, just hours after its last inspection, the dam would fail. The resulting deluge would lead to 432 fatalities and $7 million in property damage. It is considered the single worst engineering disaster of the 20th century.^[11]

9. Heppner flash flood

Lives lost: 247

Property damage: $19.5 million

On June 14, 1903, sudden and intense rains in Oregon created one of the worst flash floods in U.S. history. Within minutes rivers were overflowing toppling trees and carrying mud and debris through a narrow canyon. The flood waters were briefly held back by a debris clog, but when that burst, a wall of water overwhelmed the town of Heppner, Oregon. Houses were torn from their foundations, reducing most of the town to ruins. 247 lives were lost in the flood. Today the Willow Creek Dam, built by the Army Corps of Engineers, protects the town from this ever happening again.^[12]

Preparing for floods

You may notice that most of the floods on this list happened long ago, which again is because (with the exception of Katrina) modern technology largely enables people to evacuate from floods without such high casualties. What modern floods do lead to today is more extreme destruction of property, as our population has certainly grown substantially in the last centuries.

More than 13% of the U.S. population currently live in a 100-year floodplain (which means a 1% chance of flooding in any given year.^[13] And yet flooding isn’t currently covered by home insurance or renters insurance policies. You need to have separate flood insurance to make sure your home (or rental) is protected.

Sources