The $1.2B Central Interceptor (CI), a wastewater tunnel, will provide resilience to the current wastewater pipeline under the Manukau Harbour, as well as help Auckland manage the needs of a growing city and improve environmental outcomes. The project provides additional stormwater capacity and connectivity for future wastewater projects, allowing for increased capacity and network growth.

CI is designed to work entirely by gravity flows from Grey Lynn to Māngere Wastewater Treatment Plant (MWTP) some 14.7 km away. On route, link sewers, access points and drop shafts collect and transfer storm / wastewater into the tunnel. The design incorporates various gates that attenuate flows thus providing a controlled discharge to MWTP. In addition, CI’s design provided the most effective route to MWTP.

At 14.7 km long, CI will be the longest bored tunnel in New Zealand. CI’s depth varies between 15 and 110 metres from the surface, crossing the Manukau harbour at depths of about 15m below the seabed. With a capacity of 210,000 m3, CI will be connected to two link sewer tunnels as well as 17 above ground sites.


Image credit: Simon Runting

Role and Services Provided

AECOM, working alongside McMillian Jacobs Associates as subconsultants to Jacobs as lead designer, started the design of CI in 2014. Ghella Abergeldie Joint Venture (GAJV) was appointed in early 2019 as the Main Contractor by Watercare. Along with their design partners, AECOM continues to provide design services to the GAJV team and will continue to do so until fully operational in 2026. Our services include a range of design management disciplines.

Outcomes and Values

The project’s success is founded in a “one team” philosophy supporting a “best for project” mentality in resourcing, problem solving and decision making. This includes relationship building and close partnering to achieve Client needs. Because of the project’s long direction and changes in personnel, the use of shared technology such as Watercare’s Aconex system has enabled transfer on knowledge and documents to be well maintained. Communication using ProjectWise since inception for shared document management and submission to Client has also been effective during this long timeframe.

To further ramp up capability and capacity to cover resource shortfalls when required, key water personnel from major transport projects were actively demobilised (back-filling them from our flexible pool) to ensure Central Interceptor was on track to meet programme deadlines.

Image credit: Simon Runting