Boring of a new wastewater pipeline in New Zealand’s largest city is due start next Monday.
A 1.2m-diameter TBM will be launched to build a new outfall at Clarks Beach in Auckland to improve water quality in the Manukau Harbour.
Project manager Jason Salmon said the NZ$22m (€11.6m) outfall installation was 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,” said Salmon.
“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 66m-long diffuser will then be installed.”
The diffuser includes 22 rubber nozzles called ‘duck bills’, reflecting 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 said at the end of the TBM’s journey it would arrive at a receiving pit 10-15m 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, and then onto land.
Programme delivery manager Dave Kennerley said the outfall was a crucial part of a wider programme of work that would 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,” he said.
