Kiwi Esplanade ventilation shaft removed from Central Interceptor design

Projects, 9/05/2017
Watercare no longer intends to build a ventilation shaft near the yacht club in Mangere Bridge as part of the Central Interceptor project.

When completed, the Central Interceptor will carry wastewater between Western Springs and the Mangere Wastewater Treatment Plant. The 13-kilometre pipe will lie deep underground and will cross the Manukau Harbour below the seabed.

Earlier designs included a tunnel drop and ventilation shaft that was to be built alongside a new public toilet block near the Manukau Yacht and Motor Boat Club on Kiwi Esplanade. The drop shaft would have stood 2 metres above ground and its construction had been expected to take about 18 months.

Watercare infrastructure design manager David Ward says with further detailed analysis, engineers have found a way to do without the combined tunnel access and ventilation shaft.

“It’s a great outcome. Watercare actively engages with local communities over infrastructure projects and we do take residents’ concerns on board. Minimising any impact on our communities is always a priority and I’m really pleased that in this case we’ve found an effective alternative.”

From left: Mangere-Otahuhu Local Board member Tafafuna’I Tasi Lauese, deputy chair Togiatolu Walter Togiamua, member Carrol Elliott, chairwoman Lemauga Lydia Sosene, Watercare infrastructure design manager David Ward and local board member Tauanu'u Nick Bakulich​ 

Since the project gained resource consent in November 2013, our engineers have been focussed on optimising all design aspects of the Central Interceptor.

Ward says further modelling revealed air flow build-up at that point in the tunnel will be less than previously anticipated.

“We’ve also found a way to retain Mangere wastewater flows in the existing network without redirecting it to the tunnel, which means there’s no need for the drop shaft in this location,” Ward says.

Engineers are confident the proposed air management facilities at the Mangere Wastewater Treatment Plant, as well as those at the Central Interceptor’s May Rd site, will provide adequate ventilation.

Another reason why the shaft was initially planned was to allow access to check the tunnel-boring machine before tunnelling began under the Manukau Harbour seabed.

“Engineers are now satisfied that these checks will be able to be carried out from within the tunnel itself,” Ward says.

Mangere-Otahuhu Local Board chairwoman Lemauga Lydia Sosene says residents will be thrilled with the news that the shaft is no longer necessary.

“Our board is pleased Watercare has reviewed earlier plans, taken the time to review relevant feedback and found a way to remove this shaft from designs.

“The news will be warmly welcomed by Mangere Bridge residents and the Mangere-Otahuhu community.”

The Central Interceptor will duplicate an ageing section of the Western Interceptor, reduce the number of wet-weather overflows and accommodate Auckland’s population growth.​