A flood forms when water submerges a typically dry area. This occurs in various ways, commonly when bodies of water, such as rivers, rise over their banks.
Some of the causes of overflowing rivers include too much rain, a cracked dam or levee and quickly melting snow. A misplaced beaver dam can also cause a river to overflow to the nearby land called a floodplain.
Coastal flooding results from the seawater rushing inland due to a heavy storm or a large tsunami. Floods often form for hours or days, which is why people usually have enough time to leave any danger zone. However, some floods develop fast without any sign of danger. They are called flash floods, and they can be very hazardous as they immediately turn a small stream into a destructive gush of water capable of wiping away or carrying along various objects in its path. Moving water can destroy houses and structures, particularly those that are poorly built. It can pick up cars, trees and bridges and even cause buildings to crack and topple by tugging at the soil below.
Once the floodwater subsides, the damaged land usually becomes covered in silt and mud. Dangerous materials, such as sharp debris and pesticides, can pollute the environment. Moreover, people tend to lack access to safe drinking water, and they become vulnerable to fatal, water-borne sicknesses.