Floods

Flooding happens when a river has too much water in its channel. The water breaks through the river banks and spreads over the surrounding land.

Causes of flooding
The main cause of flooding is when a lot of rain falls in a few days. The ground becomes so wet that no more rain can trickle through the earth. This rain runs into the rivers and the water level quickly becomes much higher. The river can't cope with this extra water and the water breaks over the river banks. This happened in China in 1998.

Countries like Bangladesh, where the land is flat with high mountains, are often flooded in Spring. Snow and ice melts because the weather becomes warmer

Hurricanes, cyclones and typhoons can cause floods. These are very strong winds which form over seas and blow towards coastlines. The winds make the waves in the sea much higher. The waves then crash onto the beach and flood the flat land by the coast. This happened to the Caribbean island of Antigua in 1995.

Earthquakes shake the earth, causing big waves called tsunamis. The tsunamis travel towards the shore and flood the flat coastal land.

Unusually high tides in Spring time can cause floods by an estuary. High waves, caused by the high tide, rush up the river estuary. There is too much water in the river so the surrounding land is flooded when the river banks burst.

Dam failure can cause a flood. If engineers do not open enough of the dam holes in times of heavy rainfall, the water builds up behind the dam in the reservoir. The water can then spill over the top of the dam. This happened in Canada in 1996.

Effects of floods
The effect of a flood can be catastrophic. All these things can happen:

• Broken roads and railway lines.
• Damage to furniture and objects in houses.
• Wrecked houses.
• Crushed crops.
• The electricity and gas supplies are cut off.
• Diseases.
• People and animals are killed.
• Ornaments can be smashed.
• Electrical items like computers and TV's can be damaged.
• Carpets start to disintegrate.
• Property gets washed away.
• Trees fall over.
• Cars get smashed.
• Bridges break.

Damage to property	Damage to a bridge

Ways to prevent flooding
There are ways to prevent or minimise the damage caused by floods. People can protect their property by insurance. The insurance money will pay for repair and replacement of damaged items. But this doesn't stop a flood from happening, or prevent the damage to property.

People can put sand bags around their houses, and by cracks in doors and conservatories. Windows can also be boarded up to stop water from coming into the house.

Sandbags to protect property

If flood water does get into the house, people can use a pump to remove this water. But this takes a lot of time, and damage can still be done.

People can evacuate their houses, if there is time. They may take precious belongings, pets and essential items such as clothes, food and money. They will have to stay somewhere else during the flood. But damage is still done to the property and has to be dealt with when the owners return.

Governments can spend money to make river banks higher. Soil or concrete can be used to make the river banks higher. This is called a levee. When there is more water in the river, it should stay in the channel as the banks are higher.

Raising banks before a flood

Sometimes a flood wall can be built by the river bank to protect the town from floods. If the river bursts its banks, the water should stay in front of the flood wall. The water will not reach the town as it is trapped between the river bank and the flood wall. Flood walls are usually white.

Flood wall

Dams are also used to control floods. In times of really heavy rainfall, more holes can be opened to allow more water to flow into the river downstream. The water can be released quickly before it has a chance to build up.

Floodways are artificial river channels which can be built to divert the flow of extra water in rivers. The water then has two channels to flow through in times of heavy rainfall, meaning that the river banks shouldn't burst.

A floodway

Flood barriers can be built across rivers. These are like walls and are similar to dams. They are usually built near the mouth of a river. Flood barriers protect against floods caused by high tides or strong winds. The flood gate is closed to keep the water out of the river. In times of normal water level, the gates are kept open to allow ships to pass through. The Thames Flood Barrier is an example.