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Watercare reroutes sewer link on Central Interceptor

Watercare's central interceptor

Watercare has rerouted a link sewer to avoid community disruption and reduce emissions on the Central Interceptor project. 

The team at Watercare has found a way to reroute the first of two link sewers connecting to the 14.7 km wastewater tunnel, removing the need for a 30 m deep construction shaft at Whitney Street. 

Central Interceptor executive program director Shayne Cunis says the route change will bring great benefits for the Blockhouse Bay residents and businesses. 

“This is great news for this west Auckland community. We always try our hardest to minimise disruption during any infrastructure project and I’m really pleased our engineers came up with this innovative approach,” said Cunis. 

“The original plan included a 30-metre-deep shaft at Whitney St to allow our micro-tunnel boring machine (mTBM) Domenica to be retrieved, serviced and relaunched part way through digging the first link sewer.

Image: Watercare

“Now, instead of two shorter drives, the mTBM will complete a longer, slightly curved drive which means we won’t need the Whitney St shaft and the traffic disruption it would have caused.” 

At 1,193 m, this will be the longest mTBM drive of its kind ever completed in New Zealand. 

From next year, ‘Domenica’ will travel from the Dundale Avenue site directly to Miranda, followed by one last short drive to the existing wastewater pump station to complete its journey for the link sewer. 

According to Cunis, the design change also significantly reduces the project’s carbon footprint. 

“By removing this construction shaft, there’s a huge carbon saving – our conservative estimates put the carbon savings at 200 t of carbon dioxide equivalent.” 

This estimate takes into account materials like concrete and steel that no longer need to be used, and truck movements for spoil removal that will not be required. 

The new approach does mean the tunnelling process will take slightly longer, as the mTBM locomotive will have to travel further before it reaches the next shaft. 

However, Domenica is still on track to complete its breakthrough into the Haycock Avenue, Mt Roskill shaft in early December. 

A skeleton crew has worked on the Central Interceptor project during level 4 restrictions to prevent the TBM from sinking and normal construction activity has been able to resume under level 3. 

The Central Interceptor is expected to be completed in 2026, when it will store and transport both stormwater and wastewater to the Māngere Wastewater Treatment Plant. 

For more information visit the Watercare website

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