Floods

A flood is when a river or the sea rises so much that it spills over the surrounding land. River floods may occur after a period of prolonged heavy rain or after snow melts in sping. Small floods are common; big floods are rare. So flood size is described in terms of frequency.

A two-year foold is a smallish flood that is likely to occur every two years. A 100-year flood is a big flood that is likely to occur once a century.

A flash flood occurs when small stream changes to a raging torrent after heavy rain during a dry spell.

The 1993 flood on the Mississippi-Missouri caused damage of $15,000 million and made 75,000 homeless, despite massive flood control works in the 1930s.The Hwang Ho river is called "China's sorrow" because its floods are so devastating.

Not all floods are bad. Before the Aswan Dam was built, Egyptian farmers relied on the yearly flooding of the River Nile to enrich the soil.

After the Netherlands was badly flooded by a North Sea surge in 1953, the Duch embarked on the Delta project, one of the biggest flood control schemes in history.