Why do floods occur?
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Q:

Why do floods occur?

A:

Quick Answer

Floods occur when the ground is incapable of absorbing water from rainfall, melting snow or ice. Each spring, many regions experience warmer temperatures along with heavy precipitation. This is the ideal combination for flooding. If the ground has not completely thawed, it is even more likely to flood as there is no place for the water to drain.

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Full Answer

Flash floods occur when there is a high accumulation of water in a low-lying area within a period of six hours. These flooding events are potentially dangerous as they often result in swift-moving water knocking down trees and wiping out bridges and buildings. While flash floods happen with the collapse of a dam or other water-containing structure, they typically happen following large rainstorms.

The Pacific Ocean sends heavy rainfall to the West Coast during the winter months. The East Coast and southern United States tend to see more flooding during the summer months as moisture and warm air from the Atlantic Ocean blow inland.

Both the southeastern United States and the East Coast are vulnerable to tropical storms and hurricanes that carry the potential for flooding. In fact, sometimes hurricanes and tropical storms cause flooding in inland communities as well as coastal cities.

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    According to NOAA, most floods start with slow-moving thunderstorms, thunderstorms that travel the same path several days in a row, or hurricanes. Floating debris and ice sometimes form a temporary dam which causes the water to back up until the debris breaks free, releasing a wall of water and causing flooding downstream.

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    The National Weather Service measures floods using stream gauges in key locations across the country. During times of flooding, they measure how high the water has risen above the gauges to determine flood levels.

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    How long do floods last?

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