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Flood Home • Flood Basics • Responding to Floods • Reduce Your Risk
A flash flood is a rapidly rising and rapidly flowing surge of water that results from runoff from excessive rainfall or the failure of a dam or levee. While some floods might take several hours or days to develop, a flash flood may take only minutes, making flash floods particularly dangerous.
Flash floods most often occur within a few minutes or hours of excessive rainfall, but might also be the result of a dam or levee failure or a sudden release of water held by an ice jam. They can destroy bridges, severely damage buildings, move boulders, wash away automobiles and cause mudslides.
Two key elements contribute to the condition known as flash flooding: rainfall intensity and duration. Topography (the physical characteristics of the land, such as hills and valleys), soil conditions and ground cover also play an important role. Most flash flooding, however, is due to slow-moving thunderstorms. Heavy rains from hurricanes and tropical storms are also common causes of flash flooding.
During periods of heavy rainfall or after severe winter storms, it’s important to listen to a weather radio or your local radio or TV stations for flood information. Make sure you’re familiar with the following terminology.
Flood Watch: A flood watch means a flood is possible in your area. Be prepared to act quickly and move to higher ground if needed. Move your furniture and valuables to higher floors of your business, and put important documents in a waterproof container. Get your pre-assembled emergency supplies ready, and fill bathtubs, sinks and plastic bottles with clean water. Finally, make sure employees fill their cars' gas tanks in case an evacuation notice is issued.
Flood Warning: A flood warning means flooding is already occurring or will occur soon in your area. Be alert to signs of flooding, and if floodwaters are threatening your business, evacuate quickly to higher ground. Listen to NOAA Weather Radio or local radio or television stations for recommended evacuation routes. If you are driving and come upon rapidly rising waters, turn around and find another route.
Flash Flood Watch: A flash flood watch means that flash flooding is possible in your area. Be alert to signs of flooding and be ready to evacuate on a moment's notice.
Flash Flood Warning: A flash flood warning means a flash flood is already occurring or will occur very soon in your area. Evacuate immediately - you might only have seconds to escape. Move to higher ground away from rivers, streams, creeks and storm drains, and be sure not to drive around barricades. If your car stalls in rapidly rising waters, abandon it immediately and climb to higher ground.