Learn about the causes and impacts of floods.

How Floods Form

In 2002, heavy rains in Texas caused a reservoir to overflow. The raging water cleared everything in its path including trees, boulders ... a bridge! In just three days, the floodwaters carved a 1.4 mile (2.2 kilometers) long, nearly 20-foot-(6 meters)-deep canyon.

A flood is a rise of water with no place to go. Floods come in all depths, from just a couple inches to many feet. The power of floodwater is extraordinary and lethal. In less than an hour, strong rain can turn an ankle deep creek into an unstoppable 30-foot-high swell that overpowers everything in its path.

Floods occur all over the world. Causes of floods include hurricanes, broken levees or dams, rapidly thawing snow, ice jams, and heavy slow moving rain or repeated rains. A flood can happen in a few minutes, hours, days, or over weeks.

No matter how quickly it happens or the cause, flooding is deadly. Floods kill more people and causes more damage than other severe weather related events. Many die trying to drive or walk through a flooded area. Just six inches of water can knock a person off their feet. Just two feet of water can carry a car away.