What Are Floods? - Causes, Types & Prevention

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  • 0:05 What Are Floods?
  • 2:43 Flood Prevention
  • 5:05 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

In this video lesson, you will study floods, their causes and their effects. You will learn to identify various methods that are used to prevent floods and explore how preventing natural flood cycles can lead to dangerous flood events.

What Are Floods?

Noah should consider himself lucky; it's rare that floods of such magnitude allow so much time to prepare for a safe escape! That's because floods are times when land that is usually dry gets covered with water. While we usually have some idea when they will occur based on the weather conditions, we can never be sure just how much an area will flood or what type of damage the flooding will do.

Since floods are an overabundance of water in a normally dry area, it makes sense that they are caused by large amounts of water coming from somewhere else. Floods can come from a variety of sources, such as heavy rainfall and mountain snowmelt. If rivers, creeks and lakes receive too much water and aren't able to confine it within their banks, we can get flooding from these sources as well. It's like pouring water into an already full glass - the only place for it to go is over the edge!

This is what happened to the Mississippi River in 1927, when the river flooded 27,000 square miles of land (about the size of Connecticut, Massachusetts, New Hampshire and Vermont combined) and put much of that land under 30 feet of water. The rain that fed this flood spread the river to a width of 70 miles, claiming hundreds of lives as it poured over the land.

Coastal areas can also be flooded, and this often comes from storm surges. A storm surge occurs when a hurricane pushes a big pile of water along the ocean as it moves. Essentially, this creates a giant wall of water heading toward land. Depending on the size of the surge and how hard it hits land, it can often be the most dangerous part of a hurricane. The storm surge from Superstorm Sandy in 2012 was one of the most damaging effects of the hurricane, literally washing away homes, businesses and roads along the coast.

Flash floods can also be dangerous, since these are short-term, intense and quickly-developing floods. Think of these as happening in a 'flash.' Intense thunderstorms create temporary (but large) puddles of water everywhere and cause small rivers and creeks to suddenly overflow. The sudden pools of water that come from flash floods often occur on roadways or at low points in cities, which is especially dangerous to those driving or living where the water collects.

The main difference between floods and flash floods is the size - flash floods are small and short-term. Floods affect larger areas (usually affecting more than one state) and are more long-term, cyclical processes.

Flood Prevention

You may be surprised to learn that floods are actually a natural and beneficial process. Flood waters carry important nutrient-rich sediments downstream and onto the lands bordering the water body. This is beneficial to both human agricultural and natural ecosystems.

However, as you know, floods are also dangerous and can destroy homes and livelihoods as well. Humans have tried to control waterways for a long time in an effort to reduce flooding and provide a steady water supply. This often makes the problem worse because water doesn't like to be told what to do. When you turn on your faucet, does it take a while for the water to get there? Not at all! It's sitting, waiting and ready to come out as soon as you let it. Water is fluid and mobile - it likes to keep moving.

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