Flood is a natural event caused by excessive rainfall or melting snow. It can also be caused by human activities such as draining wetlands and building paved surfaces that don’t absorb water, which can increase the amount of runoff in a given area. Floods can be extremely destructive and are among the most costly natural disasters in terms of human suffering and economic loss.
In some cases, the water can carry pollutants such as pesticides, fuel and untreated sewage, making it unsafe for people to touch or enter. It can also erode soil, which may lead to the collapse of bridges or homes. Floods often carry large debris such as logs, cars and other man-made materials. These can be swept away in the currents, and are dangerous to be hit by or to carry. Floating wood can poke holes in tires and make vehicles unsafe to drive, and downed power lines can pose an electrocution risk.
The water from a flood can leave behind nutrients and organic material, which can improve the quality of farmland when it dries. Ancient civilizations first grew up along the banks of rivers because they provided fertile soil for farming.
A flood can happen quickly or over days. Slow-moving flood events generally pool water and take a few days to recede, while fast-moving flood events occur as water pools up, is released or flows over dams or levees due to a break or failure.