Next week New Zealand Client, Watercare will start tunnelling a new harbour outfall at Clarks Beach as part of the southwest wastewater servicing scheme. This will improve the quality of the Manukau Harbour with significant benefits for the community and environment.
On Monday, May 12th a 1.2m diameter TBM will get the ground moving on the $22M Clarks Beach Outfall wastewater pipeline.
Programme delivery manager Dave Kennerley says the treated wastewater will be discharged approximately 100m into the Waiuku Channel – a highly dynamic part of the harbour where it will quickly disperse.
“The outfall is a crucial part of a wider programme of work that will support the projected population growth of Auckland’s south-west which is expected to grow to around 30,000 people by 2050.
“Initially, it will carry highly treated wastewater from the Clarks Beach Wastewater Treatment Plant, which we’re currently upgrading. But it has been designed and sized to support future population growth in the wider area.”
Project manager Jason Salmon says the outfall installation is expected to take six or seven weeks.
“To ensure the resilience of the outfall, the pipeline will be double layered.
“The carrier pipeline, which is made from high-density polyethylene, will sit inside a steel pipe to prevent any leaks or ground and seawater intrusion.
“To install the outfall the TBM will cut through the ground and install the exterior steel pipeline at the same time.
“Once it’s reached its destination, the carrier pipe will be pulled through and plugged until it is brought into service. A 66-metre-long diffuser will then be installed.”
The diffuser includes 22 rubber nozzles called ‘duck bills’, due to their shape resembling a duck’s bill.
The nozzle design allows the periodic release of treated effluent to flow out but stops sea water flowing in.
Salmon says once the TBM finishes its journey it will arrive at a receiving pit 10 to 15m under the sea.
“The TBM will be lifted out by a team of divers who will unbolt it from the carrier pipe in the outfall, attach lift bags to it and winch it out on to a pontoon.
“Once it’s on the pontoon it will be towed to Onehunga Port and lifted back onto land.”
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