The proposed wastewater pipeline from Warkworth
Construction workers look set to break a world record in Mahurangi after Watercare unveiled revised plans for dealing with Warkworth’s wastewater.
The plans call for the boring of an underground tunnel that will carry wastewater from a pump station at Lucy Moore Park to a new wastewater treatment plant at Snells Beach.
Previously, Watercare had intended dig an open trench along Sandspit Road and lay the pipe in the trench. They had secured all the necessary consents to achieve that end.
But that plan was abandoned when it emerged that Sandspit Road – a vital link to the Mahurangi East peninsula – would need to be reduced to one-lane traffic for a period up to two years.
Watercare property manager Peter Nicoll told a Warkworth Area Liaison Group meeting earlier this month that that option “was not going to fly”.
Instead, Watercare will abandon using a trench along Sandspit Road and will seek a resource consent to drill a tunnel using a more direct route to Snells Beach.
Once completed, the tunnel will be just over 4km long – a world record for a single drive by a microtunnel boring machine.
As it happens, Mahurangi already holds the world record for another wastewater tunnel that runs from private farmland in Algies Bay to reach the ocean, just south of Martins Bay. That tunnel is 2021 metres long and was completed in August this year. It will form part of the same wastewater system as the proposed Warkworth to Snells Beach tunnel.
The Algies Bay tunnel was constructed by Watercare contractor McConnell Dowell, which has been developing expertise in the tunnelling techniques required, giving Watercare confidence that it can also construct the Warkworth to Snells Beach tunnel.
Mr Nicoll says the proposed tunnel will run 30 or 40 metres (about 10 to 15 storeys) below existing properties, so is unlikely to trouble property owners.
The depth of the pipe also means that it can’t be accidentally damaged by excavators or post-hole diggers operating at ground level.
Mr Nicoll suggested that the tunnelling technique was the way of the future.
“As more infrastructure is required for more of the Auckland region, we can’t continue to dig up people’s backyards the whole time. This is an elegant way to achieve the same result with far less impact,” he said.
The tunnel project is part of a multi-phase programme to upgrade the handling of wastewater in Warkworth and Snells Beach to cope with expected rapid population growth.
The programme includes the replacement of the wastewater treatment plant at Snells Beach, decommissioning of the treatment plant in Warkworth, replacement of a pump station at Lucy Moore Park, and the construction of an outfall pipe taking treated wastewater to the ocean.
The outfall pipe, running along Mahurangi East Road, is due to be completed by Christmas. Timing of other works is subject to securing consents and financial constraints.