Tunnelling works begin at Narooma's Wagonga Inlet to replace ageing water, sewer pipes

The 450-millimetre high-density polyethylene pipes are replacing steel pipes that installed in 1979 and "nearing the end of their useful life", according to the council.

The council said the ageing infrastructure poses environmental risks and the new pipes have double the lifespan of the steel pipes.

Council's manager of water and sewer Brett Corven said the construction company contracted to complete the works will adopt environmentally-friendly techniques to minimise impact.

"We'll use a rig that installs pipes using horizontal directional drilling, which means we only dig up ground at the ends of the pipeline to as we tunnel under the sea floor," Mr Corven said.

While drilling is completed, 12-metre lengths of polyethylene will be welded to create pipes that can be pulled into place once the tunnels are ready.

"We are installing them ahead of adjacent new piling that comes with the planned Marine Rescue Facility upgrade, and raised concerns for us with the old steel pipes.

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"We also gain efficiencies as water and waste travel more easily through the new 450-millimetre diameter high-density polyethylene pipes."

The pipes will be installed east of the Narooma Bridge, parallel to the existing pipes that run between Mill Bay and Ken Rose Park.

The council is expecting the installation to be completed by the end of November.

Ken Rose Park will be closed until works are completed, including the car park, toilets and path around the park.

From Wednesday, August 23, the section of shared path between Ken Rose Park and the Narooma Pool will be closed for seven weeks. Pedestrians and cyclists will be diverted to paths near the Princes Highway and Bluewater Drive.

Mr Corven said crews will also be set up at Mill Bay but carpark users will not be affected.

The council-funded project is part of its Integrated Water Cycle Management Strategy. For more information, visit esc.nsw.gov.au.