FLOODS

Floods are one of New Zealand’s most frequent emergency events. They happen when storms and heavy rain make rivers overflow their banks or drainage systems overflow into the streets.

Normal rainfall soaks into the soil, is taken up by trees and plants, and runs off the land to form our streams and rivers. Floods happen when there is too much water and the run-off is too much to be carried by the rivers.

There are four main types of flood:

• Rising rivers: During heavy rain rivers can overflow their banks into the floodplain. A floodplain is the flat section next to a river, and these can flood quite regularly.
• Flash floods happen when heavy rain falls in a small area with little warning.
• Coastal areas can sometimes flood because of unusually high tides or tsunami.
• Urban areas have a lot of concrete or hard surfaces which stop rainwater from soaking into the soil, so it is channelled into storm water drains. When the rain falls faster than the storm water system can manage, we get urban flash flooding. These floods usually happen very quickly and can block roads and damage buildings. Luckily, they usually don’t last very long.

Flood waters can destroy the land and wash away or damage roads, bridges, railway tracks and buildings. Crops can be flooded and livestock drowned. People have to take care and be prepared, particularly in flash floods where fast-flowing water filled with debris can sweep people away. The waters can even be strong enough to pick up vehicles.

After a major flood there will be a lot of damage and pollution to clean up. It may take months or years to recover.