Floods

Water is essential for our survival, and about 70 per cent of the Earth’s surface is covered in it, but water can also have a devastating effect. Several days of heavy rain (or melting snow) can cause rivers to burst their banks and flood surrounding areas. If the ground is already saturated with water, there is nowhere for the rain to go. The floodwater can wreck buildings, farmland and infrastructure, and can cause landslides or mudslides. If the water is flowing fast enough it can even wash people, vehicles and farm animals away.

Some floods develop slowly after a long period of rainfall. Others happen very quickly. Sometimes, a ‘flash flood’ occurs when there is intense rain for several hours and flooding happens with very little warning. This can be very dangerous when people are unprepared for the effects of the floodwater.

Many parts of the world, particularly Asia, experience a ‘monsoon season’ when strong winds change direction (from a cold area to a hot area), bringing heavy rain. Many farmers rely on the monsoon to water their land, but the rains can bring a risk of flooding, too. In other parts of the world, annual floods carry silt that helps to make the soil rich and fertile for farming. But living and working on a floodplain can be hazardous.

Did you know?

• A large vehicle like a bus can float away in just 2 feet (60 cm) of water. Fast-flowing water can knock a person down, even at a depth of just 6 inches (15 cm).
• In 2007, flash floods in Sudan, Africa, destroyed 150,000 homes and claimed over 100 lives. Three years later, in Pakistan, the monsoon season caused severe floods that claimed 1,600 lives.
• Floodwaters flow faster through narrow valleys than they do on flatter ground – and the faster they flow, the more destruction they can cause.
• After a flood, the land can be littered with debris and untreated sewage. Power supplies and clean water can also be affected. It can take a long time for people to make their homes safe to live in again.

Case Study

On 16 August 2004, the small fishing village of Boscastle in Cornwall, UK, experienced a severe flash flood. Strong winds and torrential rain brought a month’s rainfall (75 ml) in just 2 hours! The deluge caused two rivers to burst their banks, sending around 2 billion litres of water through the village, devastating homes, shops and pubs and washing cars, bridges and walls away. At its worst, a wall of water 10 feet (3 metres) high was travelling up to 40 mph (64 kph) through the valley. About 50 cars were lost to the sea and around 1,000 trees were destroyed. Amazingly, no-one lost their lives thanks to a huge rescue operation that saw over 120 people rescued in seven hours. But the flood caused millions of pounds of damage. Thankfully the village has now been rebuilt and new flood defences are in place to help protect Boscastle from future incidents.

Our Flood Resources