Tunnelling machine Domenica launches to reduce wet weather overflows

A major milestone has been reached on Watercare's Herne Bay Collector, with micro tunnel boring machine (mTBM) Domenica beginning work on the first of seven sections of the tunnel that will help reduce wastewater overflows into the Waitematā Harbour.

The Herne Bay Collector is a 1.7-kilometre-long, 2.1-metre-diameter wastewater tunnel and is a key project in Watercare’s $1.6 billion Waitematā Water Quality Improvement Programme, which will build on the environmental benefits being delivered by the Central Interceptor.

The Waitematā Water Quality Improvement Programme is one of nine work programmes in Watercare’s $15.2 billion, 10-year capital investment programme, which comprises more than 1,000 projects. 

Through the renewal of critical assets and the delivery of capital projects, Watercare is investing in resilient, future-ready infrastructure that supports Auckland’s growth, strengthens network performance and reliability, improves environmental outcomes, and ensures reliable water and wastewater services for generations to come. 

Once complete, the $260 million Herne Bay Collector will capture wet weather flows from Herne Bay's combined wastewater and stormwater network and divert them to the Central Interceptor for treatment at the Māngere Wastewater Treatment Plant, rather than allowing them to overflow into the harbour during heavy rainfall events.

The collector will be capable of diverting up to 6,000 litres per second of combined and wet weather flows to the Central Interceptor beneath Point Erin Park, significantly reducing overflows and helping deliver cleaner beaches, healthier waterways and improved environmental outcomes.

Watercare chief infrastructure officer Mark Crowle says the project is an important next step in Watercare’s long-term work to improve wastewater performance and water quality across Auckland.

"Like many older parts of Auckland, Herne Bay has a combined network where wastewater and stormwater are carried in the same pipes," says Crowle.

"During heavy rainfall, large volumes of stormwater can enter the network and exceed its capacity, resulting in overflows into the Waitematā Harbour.

"The Herne Bay Collector will help address that issue by capturing those wet-weather flows and directing them to the Central Interceptor and then on to the Māngere Wastewater Treatment Plant for treatment. It’s about making the most of the major infrastructure we’ve already invested in and progressively improving how Auckland’s wastewater network performs.

“This will mean fewer overflows into the harbour and better water quality for the harbour.”

Watercare is delivering the project in partnership with Ghella, building on the specialist tunnelling expertise, equipment and experience developed through construction of the Central Interceptor.

Crowle says the use of micro tunnelling technology also helps minimise disruption for the local community.

"We know construction can be disruptive, and we don't underestimate the impact that can have on neighbours.

"The advantage of micro tunnelling is that we can carry out most of the work underground from a series of shaft sites, rather than needing to excavate a continuous trench through Herne Bay's streets.

"That significantly reduces the amount of surface disruption required to install the tunnel."

Ghella New Zealand country director Rosario Barresi says Domenica is expected to complete her first 626-metre drive and break through around mid-next year.

“Launching Domenica is an incredibly proud moment for our team. Delivering complex underground infrastructure for Watercare and for Auckland, in such a constrained residential environment, with homes just metres from our sites, has required exceptional planning, precision and teamwork. 

“For Ghella, tunnelling is in our DNA. Five generations of our family have delivered infrastructure around the world, and Domenica carries that history in her name.

“I'm immensely proud of our people and grateful to their families, Watercare, our project partners and particularly our neighbours for their support as we deliver infrastructure that will help protect the Waitematā Harbour for generations to come.”

Waitematā Local Board chair Alexandra Bonham says the project represents an important investment in the area's environmental future.

"The Herne Bay Collector will deliver significant environmental benefits by helping reduce wet-weather overflows and improve the health of the Waitematā Harbour.

"We appreciate that work of this scale can cause disruption and we're grateful for the community's patience while construction is underway.

"The long-term benefits will be well worth it, with cleaner waterways, healthier ecosystems and more swimmable beaches for future generations to enjoy."