Stormwater Conference Awards
Project of the Year
2025
Ports of Auckland Outfall
New Zealand
At a glance
This project set out to reduce flood risk in Auckland’s East CBD and Stanley Street catchments – an area that has faced persistent flooding issues for years. It’s a key part of the city, home to critical infrastructure like Britomart Rail Station, the North Island Main Trunk line (including the future City Rail Link), Spark Arena and the Ports of Auckland.
The final phase of this major stormwater upgrade, more than two decades in the making, involved constructing a 2.5-metre diameter, 300-metre-long inverted siphon outfall. Buried up to 20 metres beneath Quay Street and the Ports of Auckland, this was the most complex part of the entire project. It was crucial to unlocking the full benefits of previous upgrades, providing essential bypass capacity and enabling the safe renewal of ageing stormwater assets.
This project set out to tackle the long-standing flooding issues in Auckland’s East CBD and Stanley Street catchments, aiming to reduce flood risk and build a more resilient future for the area.
The challenge
Auckland’s infrastructure is under increasing pressure from more frequent and intense weather events, and the East CBD and Stanley Street area is particularly exposed due to its location and terrain.
This project set out to directly address those risks by delivering a resilient, future-ready stormwater system. It marks the final phase of a 20-year programme of planning and investment, supporting Auckland’s growth while strengthening flood protection for some of the city’s most critical public assets.
Frequent flooding in this area had long impacted liveability and productivity, affecting key sites like Britomart Station, Spark Arena and the Port. The Ports of Auckland Outfall project tackled this with a New Zealand first: a tunnelled 2.5-metre diameter inverted siphon stormwater outfall, constructed deep beneath Quay Street and the Ports area.
This solution not only minimised disruption during construction but also significantly improved the catchment’s resilience - safely conveying stormwater to the Waitematā Harbour and protecting the city’s vital infrastructure for the future.
Our response
Auckland Council teamed up with McConnell Dowell and GHD to deliver a safe, innovative and cost-effective solution. By using a deep tunnel construction method, the team was able to minimise surface disruption along Quay Street and within the live Port environment.
The project brought together a wide range of stakeholders, including KiwiRail, Ports of Auckland, Auckland Transport, Ngāti Whātua Ōrākei, local businesses and various Council teams. Their input helped address concerns around ground stability, traffic disruption, safety, and operational impacts – especially in such an active infrastructure zone.
A Herrenknecht Earth Pressure Balance Tunnel Boring Machine was used to install the 2.5-metre tunnel from within the Port. The inlet and outlet shafts were structurally designed with early early involvement from the contractor, incorporating their feedback to increase construction productivity and reduce both temporary works and overall costs.
Hydraulically, we used a combination of first-principles calculations and advanced CFD modelling to fine-tune the inlet structure, improving performance while avoiding unnecessary overdesign. And with the alignment set up to 20 metres deep in Waitematā Group Rock, Class 4 reinforced concrete pipes were chosen to withstand high jacking forces and allow for a 100-year design life in harsh marine conditions.
Cultural responsiveness was also an important part of the journey. Early engagement with local iwi, site blessings, karakia, and weekly stakeholder meetings with nearby businesses helped foster open communication and strengthened the partnership approach.
The impact
Delivering this new outfall tunnel marks the successful conclusion of over two decades of strategic planning and investment in this critical area. It boosts Auckland’s flood resilience, protects important infrastructure like Britomart and Spark Arena, and creates space for the city’s continued growth.
But more than that, it shows what can be achieved when engineers, constructors, mana whenua, public agencies, and the wider community come together. This project stands out as an example of how a collaborative approach to future-focused infrastructure can deliver safer, more sustainable outcomes for everyone.