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A Flood Overview
What Is a Flood?
Devastating floods occur throughout the U.S. every year. Ninety percent of all presidentially declared natural disasters involve flooding.
Flooding is usually divided into two categories: flash flooding and river flooding. Both can cause death, injury and property destruction.
Flash floods are usually caused by slow-moving thunderstorms or thunderstorms that move over the same area one after the other. Flash floods usually occur within six hours of heavy rainfall and are usually more life threatening, according to the National Weather Service.
The majority of deaths from flooding occur when people become trapped in automobiles that stall while driving through flooded areas. Nearly half of all flood fatalities are vehicle-related.
How Floods are Formed
Several factors contribute to flooding. The two key elements are rainfall intensity and duration. Intensity is the rate of rainfall, and duration is how long the rain lasts. Topography, soil conditions, and ground cover also play an important role.
What Is a Flash Flood?
Intense rainfall in a brief period leaves more water than the ground can absorb. When this happens, flash flooding can occur.
Flash floods are usually caused by slow-moving thunderstorms or thunderstorms that move over the same area one after the other. Flash floods usually occur within six hours of heavy rainfall and are usually more life threatening, according to the National Weather Service.
Flash floods occur with little or no warning, move at very fast speeds and can reach a peak in a few minutes. They can roll rocks, tear out trees, sweep away cars and trucks, and destroy buildings and bridges. Rapidly rising water can reach heights of 30 feet or more. Flash flood-producing rains can also trigger catastrophic mudslides. You will not always have a warning that these deadly, sudden floods are coming. Most flood deaths are due to flash floods.
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