Definition of a Flash Flood

A flash flood is an instance of localized flooding usually caused by heavy rainfall, often on sloping ground. Flash floods occur rapidly and can be very powerful. The flood water can also recede rapidly.

Time Frame

• A flash flood usually happens over a relatively short period of time. The Michigan Committee for Severe Weather reports that flash floods caused by severe rain and can occur within as little as six hours, often before heavy rain has stopped falling.

Causes

• A flash flood can be caused by severe rain showers or thunderstorms. FEMA reports that melting ice and snow high up in hills and mountains can cause a flash flood, with no signs of rain in an affected area.

Dry Soil

• Flash flooding is often the result of problems with water absorption by dry, sandy soil that may be found in dry river beds. The Colorado Division of Emergency Management reports that soil in the western U.S. is often unable to absorb large amounts of water that deluge an area in a short amount of time.

Suspended Objects

• According to FEMA, a flash flood is characterized by a fast-moving wall of water that is dangerous to people, animals and objects within its path. Flash flood waters often pick up and carry objects such as rocks, mud and other debris that can be dangerous to people in the path of the flood water.

Water Levels

• Flash flood waters need not be high to sweep away people and property, because they can be extremely fast moving. Flash flood waters of as little as six inches in depth can sweep a person off his feet, and as little as two feet can move a large vehicle such as a car or bus.