New Zealand’s largest wastewater infrastructure project is now operational, marking a major milestone in Auckland’s environmental future.
Seven years after construction began, Watercare’s $1.67b Central Interceptor is now operational, delivering one of the most significant pieces of environmental infrastructure in New Zealand’s history.
Stretching 16.2 kilometres beneath Auckland, the giant wastewater tunnel will dramatically reduce wet weather overflows into the city’s streams, parks and harbours, helping restore water quality while supporting the needs of a rapidly growing population.
When construction commenced in 2019, the project represented an ambitious response to ageing wastewater infrastructure built in the 1960s. Today, it stands as a landmark achievement in engineering, sustainability and long-term city planning.
Rider Levett Bucknall (RLB) has been proud to support Watercare throughout the delivery of the project, providing cost management and quantity surveying services across one of the country’s most technically demanding infrastructure programmes. Under Ed Cook’s guidance, Associate Director Neil Kelly led RLB’s involvement on the Central Interceptor for the past seven years, providing senior commercial leadership and continuity across the project’s delivery.
Infrastructure beneath the city
The Central Interceptor is far more than a single tunnel.
Running from Western Springs to the Māngere Wastewater Treatment Plant, the network includes 18 access and drop shafts, flow control structures, grit traps, ventilation systems and new pumping infrastructure. At its deepest point, the tunnel reaches around 110 metres below the surface, passing beneath homes, parks and even beneath the Manukau Harbour.
Capable of storing approximately 226,000 cubic metres of wastewater during heavy rainfall, the tunnel significantly reduces the pressure on Auckland’s existing wastewater network and helps prevent untreated overflows into local waterways.
Delivering certainty in a changing market
Projects of this scale demand more than engineering excellence.
Throughout delivery, RLB worked alongside Watercare to provide rigorous commercial management, procurement advice and sophisticated cost modelling, helping navigate a construction market characterised by unprecedented inflation and supply chain volatility.
Using advanced risk analysis and market intelligence, the team modelled a range of commercial scenarios, giving Watercare the confidence to make informed decisions and maintain momentum during a period of rapidly changing construction costs.
“Our team is committed to providing infrastructure that makes Auckland a better place to live,” said Ed Cook, Director, RLB New Zealand.
Engineering at extraordinary scale
Few projects demonstrate the complexity of underground construction quite like the Central Interceptor.
Purpose-built tunnel boring machine Hiwa-i-te-Rangi, named after one of the stars of the Matariki cluster, became one of the defining features of the project. Measuring 190 metres long and 5.47 metres in diameter, the German-engineered machine excavated the tunnel while preventing groundwater infiltration through Auckland’s varied volcanic geology.
The project encountered everything from fine silts to hard basalt rock, requiring extensive geotechnical investigations to determine the safest and most efficient alignment.
Construction also led to an unexpected scientific discovery when crews uncovered a five-metre-thick layer of fossilised marine shells approximately three million years old, prompting collaboration between Watercare, Auckland Museum, Mana Whenua and palaeontologists to preserve and study the findings.
Sustainability built into every stage
The Central Interceptor has been recognised as New Zealand’s most sustainable water infrastructure project, achieving a Leading rating from the Infrastructure Sustainability Council.
Its design is expected to reduce whole-of-life energy and water consumption by around 40 per cent, while introducing New Zealand’s first wastewater reuse plant supplying construction water during delivery.
The project also invested heavily in community initiatives, including education programmes, local employment opportunities and partnerships supporting long-term social outcomes alongside environmental improvement.
A project that will serve generations
Reflecting on the achievement, RLB Quantity Surveyor Nilosha Pathirana, who has worked on the project from construction through to completion, described the Central Interceptor as a career-defining experience.
Working on a project of this scale has challenged me, expanded my knowledge, and strengthened my appreciation for collaboration, innovation and perseverance. I’m proud to have played my part in delivering infrastructure that will benefit generations to come.
As Auckland continues to grow towards a population of two million, the Central Interceptor provides essential infrastructure that will protect waterways, strengthen resilience and improve the quality of life for future generations.
Seven years after work first began beneath the city, one of New Zealand’s most ambitious infrastructure projects is now quietly delivering on its promise, largely unseen but with benefits that will be visible across Auckland for decades to come.
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