Floods have always been part of human history. Many ancient civilizations lived along waterways and rivers because people simply need water for their fields.
What is a flood?
A flood is a unit of water that covers a piece of land that is normally dry. Floods are common natural disasters that affect millions of people around the world. They destroy houses and buildings and take valuable agricultural land in their path of destruction. Floods can also seriously pollute drinking water, leading to disease. They are often caused by rivers, but overcrowded lakes and seas can also cause flooding. Floods are not always naturally destructive. Before the Assuan Dam was built in Egypt, the land around the Nile was flooded every year, bringing important nutrients. This made the land very fertile. This also happens every year during the rainy season in Bangladesh, but also because of this thousands of people die and millions of people become homeless.
How do floods occur?
At least once a year you see the land around the major rivers flooding. This is due to the amount of water that the rivers bring with them, due to heavy rainfall or melting snow in the mountain areas. Thunderstorms can cause flooding, where small rivers can swell more quickly and receive up to ten times the normal amount of water. Rivers that flow slowly carry water, sand and silt. They build their own bed, which allows them to grow higher than the land around them. The Huang He or Yellow River in China and the Mississippi in North America are examples of such rivers. Here you can see that the floods will slowly increase, but at the same time do more damage to the ground around it.
Tsunami
Coastal areas can also be affected by flooding. Earthquakes on the ocean floor can create a tsunami and create some waves of up to fifty feet in height, flooding the coasts many miles inland. A devastating Indian Ocean tsunami in 2004 killed more than 250,000 people in Indonesia, Sri Lanka, Thailand and other countries.
Tropical storms
Tropical storms, cyclones and hurricanes also lead to flooding. Hurricane Katrina caused massive flooding in Mississippi in 2004. Most of New Orleans had to be evacuated because of these widespread flooding.
Below sea level
Low-lying countries are in permanent danger. Much of the Netherlands, for example, is below sea level. In the past, a large part of the country was flooded by the fierce waves from the North Sea. Today, a series of dikes and dams protect the land behind the coast.
Caused by man
Floods are also caused by humans. Trees and plants normally help absorb too much water. When forests are felled or burned, the water can be generated by rainfall. As a result, barren land flows away and many mudslides arise. Too much water pressure on the dams can lead to cracks in the concrete or even lead to a dam breaking.
Flood protection
Today, flood protection is a high priority for many countries. Dams are built along the rivers to control the flow of water. They are often connected to hydroelectric power plants. In some areas, rivers are being dredged and their beds are deeper. London is protected from flooding by the ‘Thames Barrier’, a structure that rises and prevents the water from reaching a certain height. In many areas, the authorities provide quick good help for people who have suffered from floods. Special boats pick up people trapped on rooftops or the top floors of buildings. Shelters have been set up for the people who have become homeless. However, rebuilding after massive floods often takes months and sometimes even years.