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Flood protection

Flooding has occurred throughout New Plymouth’s history. Because of its proximity to Mt Taranaki and the Pouakai Ranges, our district can experience some of the highest intensity rainfall in New Zealand.

As New Plymouth and surrounding urban areas have grown, development within the stream catchments has meant that both businesses and residential properties are exposed to flooding during extreme rainfall events. New Plymouth experienced major floods in 1935, the 1970s and the 1980s.

The largest flood was in 1971 when 290mm (11.4 inches) of rain fell in 24 hours. Several shop windows in Devon Street had to be smashed by civil defence workers to relieve pressure inside the buildings - goods were then swept into the street by the floodwaters. Homes and businesses were ruined and shops incurred hundreds of thousands of dollars in damage.

In the 1980s three major earth flood protection dams were built on the Huatoki, Waimea and Mangaotuku streams to detain flood flows and to limit the flows into the central business district of New Plymouth. Since that time additional flood diversion tunnels and earth detention bunds (smaller than dams) have been constructed as part of the city’s flood protection scheme.

Stormwater structures

New Plymouth's flood protection network includes three major detention dams (Huatoki, Mangaotuku and Waimea) and two tributory detention dams (Huatoki and Fernleigh streets) along with culverts and diversion tunnels within the developed area.

The excess water, which previously would have flooded inner city areas, is detained by the dams. While ponding may still occur on some properties after heaving rainfall, our flood protection network means that water should not well up above the habitable (livable) floor level.

Stormwater system at Huatoki Dam.

Stormwater system at Huatoki Dam.

For example, in 1990 rainfall equivalent to that experienced in the 1971 flood caused widespread flooding elsewhere in Taranaki. However, flood flows in New Plymouth were controlled by the dam system, with no flood damage to the central business area.