The National Weather Service said there is “a  high risk for excessive rainfall and flash flooding is in effect for parts of these areas (of Texas) on Thursday, with the potential for an additional 6 to 12 inches of rain with isolated higher amounts possible. Storm total rainfall could be in excess of two feet for some areas before the weather finally begins to improve.”

Flash-flood emergencies were issued in five counties. Schools were closed and thousands of homes and businesses were without electricity. Some homes had as much as five feet of water inside. Law-enforcement authorities urged people to stay off the roads between Houston and the border of Louisiana. It was just about two years ago that Hurricane Harvey, a Category 4 hurricane, devastated the region and caused $125 billion in damage.

Flooding killed 83 people in the United States in 2018, the most lethal type of weather event in the nation. By comparison, only 10 people died from tornadoes last year. Floods also are responsible for about $6 billion in damage annually in this country, according to National Geographic.

Much of the severe flooding in America has occurred around the Mississippi River and in Texas, as well as along the Gulf Coast and Florida, because those areas are vulnerable to hurricanes.

Floods have shaped the history of our nation, wiping out some communities forever, and forcing others to start a new life in another part of the country.

24/7 Wall St. has created a list of the 30 worst floods in our nation’s history. We used data compiled by government agencies, including the National Weather Service, and consulted sources such as media accounts of historical weather events to develop this list.

Click here to see the worst floods in American history
Click here to read our methodology

There are three categories of floods: flash flooding, river flooding, and coastal flooding. 

The most lethal of these are flash floods, such as the one that occurred in 1972 in South Dakota that claimed 238 lives. The factors that contribute to flash floods are rainfall intensity and duration. Topography also plays a role — if the soil is too sodden with moisture, it may not be able to absorb rainfall. Flash flooding also can lead to mudslides, particularly in western states. Steep ravines and canyons can funnel high volumes of water, exacerbating flood intensity, as was the case in Colorado in 1976 in Big Thompson Canyon.

Other reasons for flash flooding are the rupture of a dam, slow-moving storms, or a surge of water released from an ice jam.

Some of the most severe flooding in our nation’s history, such as the disastrous event in 1927, occurred in areas around the Mississippi River. Hurricanes that have ravaged Florida and the Gulf Coast have brought with them storm surges that caused record damage in Louisiana in 2005 with Hurricane Katrina and in Texas with Hurricane Harvey.

Climate change has raised concerns of increased flooding and the impact that flooding from rising sea levels will have on those living on American coasts. Climatologists are concerned that melting snowfields and polar ice caps will cause more runoff and severe weather events, such as storm surges and coastal and river floods. Scientific advances, including better observational data, improved climate models, and more sophisticated detection methods have made it possible to attribute extreme weather events to rising global temperatures.

In some of these catastrophic flood events, human error, neglect, or miscalculation contributed to the scale of the disaster. In the case of the St. Francis Dam in Los Angeles in 1928, structural defects in the dam led to its collapse just two years after it was completed. At least 400 people were killed in the ensuing flood, and the calamity is the second greatest disaster in California history.

The good news is that humankind has become better at understanding the dynamics behind floods, and the use of advanced weather forecasting and satellite tracking can provide early warning. Evacuations ahead of recent hurricanes in Louisiana and Texas helped save lives.