Central Interceptor

Hiwa-i-te-Rangi completes her epic journey

On 28 March, Auckland Mayor Wayne Brown gave the order for our TBM to start up for the last time to finish the final few centimetres of her 16.2km journey since being launched from Māngere Wastewater Treatment Plant in July 2021.

At a special celebration event, 250 guests gathered around the 30-metre- deep shaft to watch the action as it was livestreamed onto a large screen. Slowly, the 5.2m diameter cutterhead emerged through billowing dust, chewing its way through the final centimetres of the concrete shaft wall—and into daylight.

Tunnellers have worked 24 hours per day, six days a week to build the tunnel. Hiwa-i-te-Rangi laid eight to 10 rings and travelled around 22 metres per day. The concrete rings are coated with a plastic liner to protect against the corrosive effects of wastewater, to ensure the tunnel lasts 100 years.

Southern section of our tunnel is ‘switched on’

Our CI project has passed an historic milestone with the southern half of the tunnel going live and operational. This section, Blockhouse Bay east to May Road (Link Sewer C), then south to Māngere Wastewater Treatment Plant, is 10.8km long. We are now one step closer to the goal of cleaner inland waterways and open spaces for central Auckland.

We held a formal celebration event on 14 February in our new pump station at the treatment plant, attended by Minister for Local Government Simon Watts, Auckland Mayor Wayne Brown, local elected members and project teams. Around 200 guests lined the pump station shaft as Mayor Brown gave an order to start up the new giant pumps. These send wastewater flows from the tunnel to the treatment plant at a rate of 1,200 litres per second.

It was an historic moment as we recognised the accomplishments of the 600 members of the Watercare and Ghella Abergeldie JV project teams, which began construction in 2019.

What are we building under there?

The Central Interceptor tunnel lies between 15 and 110 metres below the city surface and will run all the way from Pt Erin in Herne Bay to Māngere Wastewater Treatment Plant. With a diameter of 4.5m, the tunnel will be high enough to fit a standing giraffe inside.

Along with two smaller-link sewer tunnels also under construction, the main CI tunnel will collect wastewater from the existing network and take it to Māngere, with a controlled flow rate. The tunnel slopes at a gradient of 1:1000 so wastewater can flow downhill to Māngere.

The budget for this epic seven-year project is $1.668 billion.

Construction updates

We have 17 construction sites along the tunnel route, with some operating for three to five years, with smaller sites open for around 24-36 months.

At the bottom of the page, you can see what’s going on at each site.

The technology behind New Zealand’s largest wastewater project

To dig the main CI tunnel and lay the concrete segments behind it, we used state-of-the-art tunnel boring machines (TBMs). These gigantic machines enable us to excavate (or ‘bore’) through a wide range of ground conditions.

Infrastructure constructed by these powerful TBMs is strong and reliable and is set to last at least 100 years.

Engaging with locals

We want to update you on the construction process and hear your feedback. If you live or work near one of our sites, you’ll get a bulletin, newsletter, notice or letter, or an invitation to a public event, depending on the information we have to share.

Email us your feedback.

Supporting our wider community

Although it’s being built to last 100 years, the ambition for the project extends well beyond construction. We also want to help improve the wellbeing of communities along the tunnel route.

To support this, a cultural outcomes group is providing advice as the project progresses. This group comprises people from mana whenua, our Watercare team and contractors. Check out some of our activities.

Protecting our environment

As well as delivering significant environmental benefits such as cleaning up our waterways, we’re committed to leaving our construction sites and their surrounds in a better condition than when we arrived.

Learn more about our plans, initiatives and practical actions in the areas of sustainability and the environment.