Central Interceptor

Ground-breaking benefits for Tāmaki Makaurau

Since 2019 we’ve been busy constructing New Zealand's largest wastewater tunnel to manage our central city’s wastewater, called the Central Interceptor (or ‘CI’). It’s all about everyone enjoying cleaner inland waterways and open spaces across the central city.

Right now, in older parts of the city, wastewater and stormwater flow into a combined network of pipes. When it rains heavily, stormwater often overwhelms the ageing system, resulting in wastewater overflows into our creeks and streams.

The CI tunnel will significantly reduce overflows in the central Auckland area.

What are we building under there?

Once completed in 2026, the tunnel will lie between 15 and 110 metres below the city surface and 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.

Check out our travelling Discovery Centre

Grab the whānau and join us for an awesome experience including virtual reality, outdoor games and a movie ride to learn all about the CI tunnel. Here's where our Discovery Centre will be in January:

• Tues 14 to Sun 19, 9am-5pm daily: Funfest 2025, Due Drop Events Centre, 770 Great South Road, Manukau

• Sat 18, 10am-12.30pm: Summer Fun in the Park, Olympic Park, Portage Road, New Lynn

• Mon 27, 10.30am-12.30pm: Little Scientist, Herne Bay Playcentre, 211 Jervois Road

• Fri 31, 6pm-9.30pm: Blues at Blockhouse Bay, Blockhouse Bay Reserve, Endeavour Street

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’re using state-of-the-art tunnel boring machines or 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.

Meet Hiwa-i-te-Rangi: a truly ground-breaking machine

Hiwa-i-te-Rangi is the giant TBM working tirelessly to grind a 16.2 km journey, using her massive cutter head.

TBMs are traditionally given female names in honour of the patron saint of miners and tunnellers, Saint Barbara.

To find a name for our main TBM, we asked for ideas from children in schools along the tunnel route. They chose Hiwa-i-te-Rangi, a female Matariki star, which they believed represented our aspiration to improve the natural environment.

Hiwa-i-te-Rangi is in great company, working alongside our smaller TBMs, Dominica and Victoria (and our training TBM, Kate).

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.

You can also come along to our interactive travelling Discovery Centre to know more about what’s going on and have some fun at the same time (details above). 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 well-being 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.