Watercare reaches key milestones in Clarks Beach wastewater outfall installation and plant upgrade

Watercare is making good progress on the Clarks Beach Wastewater Outfall, with the final of three diffuser sections now successfully installed.

This milestone follows the completion of tunnelling works for the outfall and marks a crucial step forward in delivering essential wastewater infrastructure to support projected growth in Auckland’s south-west, which is expected to reach approximately 30,000 people by 2050.

The outfall, alongside the Clarks Beach Wastewater Treatment Plant upgrade are the first two projects Watercare will bring into service as part of its $500 million servicing scheme for Auckland’s south-west communities.

Watercare programme delivery manager Dave Kennerley says the outfall will initially carry highly treated wastewater from the upgraded Clarks Beach Wastewater Treatment Plant.

“Both the outfall and the upgraded treatment plant are progressing well and are expected to be completed by June next year.

“The outfall will store and discharge treated wastewater approximately 100 metres into the Waiuku Channel – a highly dynamic part of the harbour where it will quickly disperse.

“It has been designed and sized to support future population growth in the south-west and in the future will also discharge treated wastewater from Waiuku.

Watercare project manager Jason Salmon says work to install the 66-metre-long diffuser began early last month after completing the piling work to establish a solid foundation for the diffuser.

“The diffuser is a critical part of the outfall that will periodically release treated wastewater on the outgoing tide but stops sea water from flowing in.

“To install the outfall safely in the Waiuku Channel, we installed it in three sections – each weighing around nine tonnes.”

Salmon says each section took approximately 10 to 15 days to install and involved a detailed sequence of work, starting with pre-assembly at Onehunga Wharf.

“From there, each section was lifted and secured onto a barge, which transports it to the installation site in the Waiuku Channel.

“Once it was transported to site, each section was carefully lowered, secured to the support piles, and connected into the outfall approximately five metres below low tide levels.

“To hold it in place, our crews used specially-designed couplings fixing the diffuser to the piles.”

Clarks Beach Wastewater Treatment Plant upgrade

Significant progress has been made on the Clarks Beach Wastewater Treatment Plant upgrade, with two new ultraviolet (UV) filtration units now installed.

These UV filtration units will enable the plant to treat over five million litres of wastewater per day – more than double its current capacity.

Photo: The new UV units installed at the Clarks Beach Wastewater Treatment Plant.

These units are the essential last step in the process ensuring that bacteria and viruses are neutralised.

A new chemical dosing area and storage facility has been installed.

“These will hold the chemicals necessary for the advanced biological treatment processes enabled by the new membrane-aerated biofilm reactor and membrane bioreactor (MBR) technologies installed as part of the upgrade.

“Having this sophisticated technology will allow the plant to produce exceptionally high-quality treated wastewater, which ultimately benefits the harbour.”

Kennerley says the next milestone on the cards is cold commissioning later this year, which involves testing the new equipment with water to ensure operational readiness.

“Once completed, the team will move to hot commissioning with live operating conditions.

“While work takes place at Clarks Beach, we now have other crews out working on the wider programme. They are carrying out geotechnical investigations and surveys and we will be starting the first major upgrade work at the Waiuku Wastewater Treatment Plant early in the new year.”