The tunnel & associated sites

The  Northside Storage Tunnel forms a complete underground system from North Head, near Manly, to the Lane Cove overflow site on the western side of the Lane Cove River.

There's a junction at Tunks Park, 9.5 km west of North Head. From this junction, a 3.7 km, branch tunnel runs to Scotts Creek near Castle Cove.

There are also large underground caverns at North Head and Tunks Park. They were originally built to park tunnel boring machines, store equipment or as underground workshops. They're now used for ventilation.

Key sites

We have tunnel ventilation equipment at Lane Cover River West and Scotts Creek.

Air ventilation facility.

Tunnel ventilation at Lane Cove River West is an important part of the Northside Storage Tunnel. 


If wastewater levels rise above a certain point at these sites, control gates or penstocks open and channel the overflow into the tunnel.

If the tunnel capacity nears 70 million litres in wet weather, the flow of the air is reversed.

The ventilation fan at North Head is automatically turned off and ventilation fans at Lane Cove and Scotts Creek start up. As the tunnel fills, air is extracted by the Lane Cove and Scotts Creek fans.

Air that's discharged from the Lane Cove and Scotts Creek sites passes through three filters before being released into the atmosphere. The filters include a:

  • pre-filter
  • granular activated carbon filter
  • final filter.
Parkland with a door in a rockface

The Northside Storage Tunnel includes many facilities.

We manage overflows through a fixed-level weir.

If an overflow occurs, a siphon would be activated to channel the diluted wastewater into an underground pipeline and finally into the tunnel.

All equipment at the Quakers Hat Bay site is underground.

It's connected to the Northern Suburbs Ocean Outfall System (NSOOS).

If the flow of diluted wastewater rises in the NSOOS, it's channeled into the Quakers Hat Bay site and into the tunnel.

If the tunnel is full, an isolation control gate or penstock closes. This channels the overflow into a purpose-built weir and discharges it into Quakers Hat Bay.
At Shelly Beach, a weir collects any overflow from the Manly Ocean Outfall System (MOOS) and channels it into a borehole that flows into the Northside Storage Tunnel.

If the tunnel is full, the overflow is discharged into the ocean. The Marine Parade outfall, near Shelly Beach, is no longer needed.
Aerial view of North Head Wastewater Treatment Plant looking westwards

North Head Wastewater Treatment Plant is on the coast near Manly.

The cliff face bypass weir and siphon at North Head Wastewater Treatment Plant's inlet channel prevents underground flooding if there's power or major equipment failure.

The tunnel reduces the need for the cliff face discharge by allowing wastewater to divert into the tunnel during power or major equipment failure.

The tunnel pumping station is monitored and controlled by the plant’s SCADA (Supervisory Control and Data Acquisition) system.

We monitor all sites 24-hours a day, seven days a week.

All data is recorded and sent via telemetry to our Systems Operations Centre (SOC).

We track, monitor and report all critical data and assess and respond to any alarms.

Although the Systems Operations Centre coordinates communication for all sites, each site is designed to operate safely and independently if there's a communications failure.