A flood is a body of water that covers land which is normally dry. Floods are common natural disasters that can affect millions of people around the world. They destroy houses and buildings, and carry soil away from valuable farming land. Floods can also contaminate drinking water and lead to diseases. They are often caused by rivers, but overflowing lakes and seas can also cause flooding.
Flooding has always been a part human history. Many ancient civilizations developed along waterways and rivers because people needed water for their fields.
Floods are not always destructive natural events. Before the Assuan High Dam was built yearly floods in Egypt brought along nutrients and made the land around the Nile very fertile. Every year floods during the monsoon season in Bangladesh deposit fertile soil but also kill thousands of people and leave millions homeless.
Flooding near Key West, Florida - Marc Averette
How do floods occur?
At least once a year the plains around large rivers are flooded. This is due to the amount of water that rivers bring with them, because of heavy rainfall or melting snow in the mountainous regions. Thunderstorms can cause flash floods, in which small rivers can swell quickly and carry up to ten times the normal amount of water.
Rivers that flow slowly carry water, sand and silt. They build up their own beds, making them higher than the land around them. The Huang He, or Yellow River, in China and the Mississippi in North America are examples for such rivers. Flooding here builds up slowly but causes more damage because more land is affected.
Coastal regions can also be affected by flooding. After earthquakes on the ocean floor tsunamis can bring up to 15-metre high waves and flood the coast many miles inland. In 2004, a devastating tsunami in the Indian Ocean killed over 250,000 people in Indonesia, Sri Lanka, Thailand and other countries.
Tropical storms, cyclones and hurricanes also lead to flooding. Hurricane Katrina caused a massive flooding of the whole Mississippi Delta in 2004. Most of New Orleans had to be evacuated because of widespread flooding.
Low-lying countries are in permanent danger of being flooded. A large section of The Netherlands, for example, lie below sea level. In the past, ocean water from the North Sea flooded much of the country. Today a series of dikes and dams protect the land behind the coast.
Floods are also caused by humans. Trees and plants normally help absorb too much water. When forests are cut or burned down, water from rainfall flows down barren land and produces mudslides. Too much water pressure on dams can lead to cracks in the concrete or even cause a dam to break completely.
Flooded village in Sumatra after 2004 tsunami
Today flood protection has a high priority in countries that are in danger. Dams are built along rivers to regulate the flow of water. They are often connected with hydroelectric power plants. In some areas rivers are dredged and their beds are laid deeper. In alpine regions reservoirs are built to hold back water and control the flow of small rivers.
In many areas, authorities provide quick and unbureaucratic help for people who have suffered from flooding. Special boats pick up people who are trapped on roofs or on the upper floors of buildings. Shelters are set up for people who are left homeless. Rebuilding after massive floods often takes months and sometimes even years.
- The Delta Works - The Netherlands Fight Against the Sea
- Thames Barrier - Protecting London From Flooding
- The North Sea
- Venice - City of Canals
- The Monsoon Dominates India's Climate
- Hoover Dam - Flood Control and Electricity for the Southwestern USA
- Hurricanes and Tropical Storms
- El Niño - Climate Changes in the Pacific Ocean
- The Nile River
- China's Yellow River is Dying
- Kiribati in Danger of Disappearing into the Ocean
- Climate Change Threatens Vietnam's Rice Production
- absorb = take in
- affect = to have an effect on
- ancient = old
- authorities = people who work in government organizations
- barren = without vegetation
- barrier = wall, blockade
- bed = flat ground at the bottom of a river
- build up = create
- certain = special
- coastal = where sea and land meet
- common = something that happens often
- concrete = material used for making buildings; it is made up of water, stones, cement and sand
- contaminate = poison; to make something dirty so that you cannot use it any more
- crack = small break
- cyclone = tropical storm
- damage = destruction
- delta = an area where a river divides itself into many smaller rivers and flows into the ocean
- deposit = leave a layer of material in a place
- destroy = damage completely
- destructive = causing damage to people or things
- devastating =shocking, destructive
- dike = wall to keep back water from flowing into land that lies lower
- disaster = an event that destroys things and can kill or hurt many people
- disease = illness
- dredge = to remove mud from the bottom of the sea or a river
- due to = because of
- earthquake = when the crust of the earth suddenly moves; earthquakes cause a lot of damage
- evacuate = to bring people away from a dangerous place
- fertile = here: if soil is able to produce good food or crops
- flash flood = heavy rain that covers a region with water in a very short time
- homeless = without a place to live
- hydroelectric power plant = building located on a river or high up in the mountains that produces electricity from the power of water
- inland = away from the coast
- massive = great, very much
- melt = when snow or ice turn into water
- monsoon = heavy rain that falls in many parts of South Asia between April and September
- mudslide = when a lot of wet earth suddenly falls down the side of a hill; this usually happens after heavy rainfall
- nutrient = chemical or food that gives plants what they need to grow
- occur = happen
- overflow = if a river or lake is so full of water that the material inside moves over its edges
- permanent = never-ending; something that is here to stay
- plains = large flat areas of land
- priority = importance
- protection = defense, safety
- rebuilding = to build again after something has been destroyed
- regulate = to control
- reservoir = a man-made lake where water is kept
- sea level = the average height of the sea
- section = part
- shelter = place to live
- silt = sand, mud and soil that a river carries ; it slowly settles down to the bottom
- soil = the top part of the earth
- suffer = to feel pain
- swell = to become larger
- thunderstorm = storm with thunder and lightning
- trap = if you cannot escape from a place
- tsunami = very large ocean wave caused by an underwater earthquake
- unbureaucratic = without forms to fill in
- valuable = important