Why we're building the Central Interceptor

What it’s all about?

In older parts of central Auckland, wastewater and stormwater flow into a combined network of pipes. When it rains heavily, stormwater can overwhelm these pipes. Unfortunately, this means that wastewater overflows with stormwater into our creeks and streams.
 
We want everyone to be able to enjoy clean waterways and open spaces, so we’re building a $1.2 billion wastewater tunnel across central Auckland called the Central Interceptor (CI). We also have other projects in the western isthmus, such as separating the stormwater and wastewater pipes. Together, the Central Interceptor and our western isthmus strategy will significantly reduce wastewater overflows in the area.
 
Image stating some of the key facts about our Central Interceptor wastewater tunnel

New Zealand's largest bored wastewater tunnel

The Central Interceptor (CI) tunnel is 4.5 metres in diameter and will run for 14.7 kilometres from Grey Lynn under central Auckland and the Manukau Harbour to Māngere. The tunnel will lie between 15 and 110 metres below the surface. Along with two smaller link sewer tunnels we are building, the main CI tunnel will collect wastewater from the existing network and take it to the Māngere Wastewater Treatment Plant.

We’re using state-of-the-art tunnel boring machines (TBMs) from Germany to build the tunnel. It will slope at a gradient of 1:1000 so the wastewater can flow downhill to Māngere.

Above ground there are 16 construction sites. There, we are creating permanent access shafts and drop shafts along with control and overflow structures, and air treatment facilities for future operational use.

The project, which is the largest wastewater project in New Zealand's history, offers a number of key benefits.

Photo of a stream that will be cleaned up thanks to the Central Interceptor project

Cleaner waterways and beaches

Stormwater overflows will be significantly reduced in the central Auckland area.
Seedling replanting

Greener parks

We’ll leave public spaces in a better condition than we found them by planting two trees for every one we remove.

Photo of Norgrove lava rock forest that will benefit from the Central Interceptor project

Restored habitats

We’ll plant trees and remove weeds and pests to bring the Mt Albert Norgrove lava rock forest back to life.

Photo of a lady and two children planting trees at Mt Albert

Improved open spaces

Together with local environmental groups, schools and Auckland Council, we’ll plant native plant species in our parks and reserves.
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