How do we manage the risk of flooding?

Ponding in Strand Park after the February 2004 flood on the Hutt River

Many of the region's floodplains are highly developed, which means a lot of people live there, with houses, buildings, roads and other assets close to a river. The most developed floodplains are the Hutt, Otaki, Waikanae, Porirua, Waingawa and Ruamahanga floodplains.

Cities and towns such as Lower Hutt, Upper Hutt, Otaki , Waikanae, Paraparaumu, Greytown, Carterton, Masterton, Tawa and even parts of inner Wellington face a risk of flooding.

Each river is managed differently to prevent serious flood damage and to protect people and their assets. GW Flood protection works cannot stop a river flooding, but they can try to keep floodwaters within a river channel and stop them from reaching houses and businesses. Some of the flood protection measures used include:

• Structural measures such as building stopbanks and floodgates, gravel extraction and making bridges higher.
• Other non-structural measures such as providing information to the public and schools about what to do in a flood, managing the river day to day, having a flood warning system and having rules about where people can build houses.

How do we measure floods?

Floods are measured by the amount of water flowing in a river. The measurement is called a cumec and stands for cubic metres of water flowing past a point every second. From this measurement we can work out how likely it is for a certain sized flood to happen.

For example, a flood on the Hutt River flowing at 1900 cubic metres per second, is statistically likely to happen every 100 years.

However, don t be misled into thinking that a 100-year flood will only happen every 100 years. Two floods of this size could happen soon after each other.