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Floods

Key Messages About Floods

  • Floods are New Zealand’s number one hazard in terms of frequency, losses, and declared Civil Defence Emergency Management emergencies.
  • The best thing you can do to protect yourself and your whānau is get ready. Make and practise your emergency plan, have a grab bag and emergency supplies in case you need to evacuate.
  • Your regional council will be able to tell you about the flood risk is in your area and may be able to provide information and resources to reduce potential damage.
  • Stay up to date with the latest weather information from MetService, Te Ratonga Tirorangi, New Zealand’s National Weather Service. Pay attention to Watches and Warnings which are also available on the MetService mobile app.
  • Put safety first. Don’t take any chances. Act quickly if you see rising water.
  • Never try to walk, swim, drive through or play in flood water.
  • Listen to the radio for updates and check the websites of your Regional Council and your local Civil Defence Emergency Management Group. Follow any instructions from local Civil Defence authorities or emergency services regarding evacuation of your area.
  • If you have been evacuated, it may not be safe to return home even when the floodwaters have receded. Listen to emergency services and local Civil Defence authorities and don’t return home until they tell you it is safe to do so.
  • Stay away from damaged areas. Your presence might hamper rescue, obstruct other emergency operations and put you at further risk.
  • If your whare/home has been affected, it is important to clean and dry your house and everything in it and protect yourself while you do it. Floodwater may contain sewage and other hazardous materials which can contaminate your whare/home.
  • Ensure you contact your utility suppliers if your utilities have been affected by water or debris (e.g. contact your gas supplier if your gas meter has been affected).

Floods

A flood is when water covers land that is normally dry. Floods are usually caused by heavy or prolonged rainfall, but can also occur due to landslides triggered by heavy rainfall or earthquakes, failure of dams, high sea levels at river mouths, coastal storm inundation, and tsunami.

Floods happen frequently in New Zealand and can cause a lot of damage to buildings and lifeline utilities, as well as injuries and loss of life.

Flooding may be caused by rainfall some distance away. Many of New Zealand’s rivers are quite long, and heavy rain in the upper part of their catchments can result in flooding a long way downstream.

Types of Flooding

There are different types of flooding:

River flooding generally happens during heavy rain, when rivers overflow their banks into the floodplain. A floodplain is the flat section next to a river, and these can flood quite regularly. 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.

Surface flooding can happen when heavy rain falls either in a small area or in an urban area with lots of hard surfaces that stop rainwater from soaking into the ground. Usually, surface flooding starts quickly but doesn’t last very long. It is often associated with thunderstorms and short, intense rainfall.

Groundwater flooding can happen during periods of unusually high rainfall, when the rising water table causes water to rise out of the ground. Groundwater flooding can bubble up and start flowing along the surface and can also rise up directly in homes.

Flash floods occur rapidly. They are usually the result of intense rainfall which overwhelms natural or urban drainage systems, and they usually affect small areas. Flash floods often appear as a torrent, can carry rocks, mud and other debris, and can sweep away most things in their path.

The isolated rain shaft as it strikes central Blenheim (Credit - Diana Wadsworth)

Storm surges are produced when high winds push water onshore. They can cause beach erosion and threaten life and property. Storm surges are most common at the coast, where severe weather can cause extreme tides. Storm surges can also happen at large lakes.

Flood Hazards

Floods are New Zealand’s number one hazard in terms of frequency, losses, and declared Civil Defence Emergency Management emergencies. They can cause property and land damage, injury and loss of life.

  • Floodwaters can damage buildings, land, and lifeline utilities, including roads, bridges, power lines and phone lines. Crops can be destroyed and livestock drowned.
  • Fast-flowing water is often filled with debris, and it is strong enough to sweep people away. Floodwater can even be strong enough to pick up vehicles.
  • Dangerous chemicals and biohazards can enter floodwater from the ground surface, septic tanks and sewage systems. This can contaminate drinking water, land and any surfaces it touches.
  • Flooding can cause major damage to houses, and families can face months away from home while their homes are being repaired.
  • The majority of flood deaths are vehicle-related – caused by driving through flood water or attempting to move a stranded vehicle. As little as 30 centimetres of water can cause you to lose control of a vehicle, including SUVs. The depth of the water is not always obvious, stopping you from seeing hazards like potholes or washouts. Rapidly-rising water may stall the engine, engulf the vehicle and you and the vehicle can be quickly swept away by rapidly-rising water.

If you live in a flood-prone area, the best thing you can do is prepare yourself, your whare/home and your whānau/family. Floods can cause major disruption to whānau/family life – you might have to leave your whare/home and you could lose some or all of your possessions - and the emotional impact can be profound. But there are things you can do to reduce the risk and ensure you are prepared.

Useful Links

Get Ready Website

Grab Bag
Emergency Supplies

MetService Website

MetService
MetService Warnings and Watches

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