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What is a Flash Flood and What Causes it?

A flash flood is a flood that happens quickly and without warning. It occurs when there is a powerful torrent of water coming in all at once, very fast, in one place. Because the ground or sewers cannot absorb the water fast enough, it becomes an intense and damaging flood. Some causes of a flash flood are:

Rainfall intensity and duration. A flash flood is not just caused by heavy rain but by how long of a time the rain falls. The heavy rains are usually caused by a hurricane, a thunderstorm that is moving unusually slow, or a storm passing over the same area more than once.

Infrastructure failure. If water infrastructure like a dam or levee fails, water can flood an area in minutes. Most sewers are not equipped to handle that amount of water all at once and will fail in the event of a dam or levee break.

Topography and soil. As mentioned, if the ground cannot absorb rain at the pace it is falling, a sudden flood can happen. In the winter, rivers can also experience what is called an ‘ice jam’ where accumulated ice blocks water flow. This causes unexpected ‘upstream floods’.

Most people who die in floods were caught in a flash flood. Do what you can now to learn how to prepare for a flood and get familiar with your local flood warnings!