Cleaner beaches Herne Bay

With the Government announcement in May of the Local Water Done Well programme, we now have more certainty on funding our $1.2b annual infrastructure budget. We are therefore renewing our commitment to the Herne Bay project for completion in 2028.

Project overview

The Cleaner beaches Herne Bay project, in parallel with the Central Interceptor extension to Point Erin, will collect combined wastewater and stormwater overflows for safe treatment at Māngere Wastewater Treatment Plant. This new infrastructure will significantly reduce overflows into the environment and improve the quality of inland waterways and swimmable beaches by the end of 2028.

The project consent we have been granted permits installation of approximately 1.5km of a 2.1m-diameter trunk sewer line (the tunnel) using a Tunnel Boring Machine (TBM). This pipeline will pass beneath the road at depths ranging from 9-22 metres.

As part of these works we will also:

• Install eight tunnel shafts, along with intercepting shafts connections to existing engineered overflow points (EOPs)

• Install small diameter pipelines along Marine Parade (600mm in diameter) and local connections to the existing engineering overflow points (between 200mm to 450mm in diameter). These will be constructed via open trenching.

• Establish two temporary Construction Support Areas (CSAs) one at Salisbury Reserve and the other in the area beside the Curran Street motorway on-ramp.

Construction will occur sequentially over different road sections. We are working towards a start date of late-2025 for a 36-month construction programme. At present we are in design mode and will shortly begin the contractor selection process. We will provide updates as we approach each major project milestone.

The map below shows the location of the proposed works along with existing infrastructure and the Central Interceptor tunnel.

Point Erin Park: south-west corner works

In addition to the Herne Bay collector, we are building a plant room and control chamber for connections to the Central Interceptor tunnel. We will bring you more details about this aspect of the project when they are available.

St Marys Bay and Herne Bay separation projects

What were the original projects?

These projects were part of the earlier works that focused on separating the old, combined stormwater and wastewater pipes directing stormwater to the environment and wastewater to the Māngere Wastewater Treatment Plant via the Ōrākei main. The project included a new public wastewater network, storage and a new pump station at Point Erin as well as private property drainage separation and connections. Work has been progressing for the past 18 months on the design and approvals for the St Marys Bay separation works.

Why has a change in programme been proposed?

Like most infrastructure projects, the St Marys Bay and Herne Bay wastewater and stormwater separation projects have been heavily impacted by escalating material, labour and traffic management costs. These increases, coupled with further costs identified in the design stage to accommodate geotechnical risks, and further learnings taken from the recent separation project at Okahu Bay, put our most recent cost estimates for the project at $278m, double the original forecast of $136m.

This scale of change is unaffordable and as a result our team and Auckland Council have been exploring a new, more cost-effective way to deliver the same water quality outcomes within the agreed timeframe.

What is the new proposal?

Fortunately, an alternative more affordable option is available. This involves an extension of the Central Interceptor wastewater conveyance and storage tunnel from Tawariki Street in Grey Lynn to a new connection shaft in Point Erin. This will be supported by the new Herne Bay collector and a revised programme of sewer separation which will be managed by Healthy Waters moving forward.