Watercare’s $1.6b Central Interceptor is New Zealand’s largest wastewater infrastructure project; a 16.2 km super-sized tunnel plus two intersecting link sewers running beneath Auckland city and under the Manukau Harbour. The tunnel will significantly reduce wet-weather overflows and clean up beaches and streams. The new wastewater infrastructure will also cater for growth and increase the resiliency of the existing wastewater network.
Construction began in 2019, and a massive tunnel boring machine (TBM) named Hiwa-i-te-Rangi began her tunnelling journey in July 2021.
In February 2025, a key milestone was reached when the southern half of the tunnel—a 10.8 km section from Blockhouse Bay east to May Road (Link Sewer C), then south to the Māngere Wastewater Treatment Plant was officially commissioned. Mayor Wayne Brown gave the order to start up the pumps at a giant new pump station, to send tunnel flows to the treatment plant for processing. Each one of the six pumps is capable of moving 1,200 litres per second of wastewater.
Six weeks later, Hiwa-i-te-Rangi broke through the final shaft wall at a construction site in Point Erin, Herne Bay after laying more than ten thousand tunnel rings. Each ring is coated with a corrosion-resistant plastic liner, ensuring the tunnel’s design life of 100 years.
The Central Interceptor project is on track for completion in 2026. The tunnel will be able to store and convey more than 250,000 m³ (around 99 Olympic swimming pools) of combined stormwater and wastewater. A 1:1000 gradient will allow flows to travel hill downhill from Herne Bay to Māngere treatment plant.
AWMA’s Role in the Central Interceptor Project
AWMA was engaged by the head contractor, the Ghella Abergeldie Joint Venture (GAJV), on behalf of Watercare, to deliver engineered water control solutions for this complex system of shafts, chambers, and pump stations.
Our scope of works includes:
- Hydraulically actuated penstocks
- Electrically actuated penstocks
- Stop logs and stop plates
- Flap gates
- Hydraulic control systems (HPUs and pipework)
All gates are custom-manufactured from Duplex 2205 and 2507 stainless steel, delivering the strength and corrosion resistance required for long-term performance in a challenging wastewater environment.
Partnership in Progress
This has been a long-term collaboration, with years of design development, testing, and refinement to meet strict operational and installation demands.
Key achievements to date include:
- Keith Hay Park – Fully installed hydraulic systems, including HPUs in the plant room and gate assemblies within underground chambers.
- Māngere Pump Station – Supply of two of the largest stop log systems ever manufactured by AWMA.
- PS23, Haycock Avenue & Māngere Treatment Plant – Gate systems now installed and operational.
With multiple sites still scheduled, AWMA continues to provide precision-engineered solutions that help deliver this vital piece of national infrastructure.
Project Snapshot
- Length: 16.2 km main tunnel (+ two link sewers under construction, totalling 4.3 km)
- Internal diameter: 4.5 m (tall enough to stand a giraffe inside)
- Depth: 15 m – 110 m below ground
- 17 construction sites, including 19 shafts
- Budget: $1.668 billion
- Capacity: 250,000 m³ (99 Olympic swimming pools)
- Completion: 2026
Delivering Long-Term Performance
AWMA is proud to contribute to this landmark project, ensuring robust and efficient water control infrastructure that will support Auckland’s growth for generations. Through innovation, engineering excellence and collaboration with our project partners, we are helping to build a cleaner, healthier city.
- Photos courtesy of Watercare.
