Impacts of 7 years of Construction

Impacts of construction – Balgowlah & Seaforth


Balgowlah Golf course and a site near Kirkwood St, Seaforth will become construction sites for drilling, rock crushing, provision of concrete lining for the tunnel and removal of waste materials dug from the tunnel, for the 5-7 years of construction.

Hours will be 7am-5pm weekdays and 7am-1pm Saturdays, plus night work where integration with existing roads and traffic management is needed – with associated road closures and delays.


Noise, dust and traffic disruption from truck movements will have significant impacts on residential areas surrounding the sites. Other tunnelling projects in Sydney have involved trucks movements of up to one every minute, plus the impacts of trucks queued to access the site, and travelling on local roads.

An example of the noise and disturbance generated by construction at a similar site in St Peters is below (filmed by residents at 1am).


Acoustic sheds and noise walls are used to attempt to reduce the noise and dust generated from construction, but residents will still be severely impacted because they are within 100m of the site, or located on hills elevated above the site where noise walls will not be effective.


Dust particles, particularly silica dust, are generated from construction and are dispersed through truck and equipment movements, open construction areas, and fine particles carried through unavoidable air movements. Silica dust is well known to cause respiratory diseases, and long term exposure at close proximity to the site is a significant health risk to residents.

Impacts of construction – Seaforth, Mosman and Middle Harbour


Spit Reserve West is planned to become a construction site for the tunnel that will be laid on small stilts embedded on the harbour floor from Seaforth Bluff to Clive Park, Northbridge.


A large pontoon attached to the reserve will be used for construction – including use as a concrete plant to construct and fit-out giant steel tubes for the tunnel that will be floated in by barge. Barges will also be used to remove spoil and other materials from the site.


Large coffer dams (50m x 25m on the surface, and up to 40m deep) will be used in Middle Harbour to allow tunnel construction on the harbour bed. These will be in place for the majority of construction to allow drilling, spoil removal, pumping of waste water and tunnel connections. Some moorings will also need to be moved temporarily to allow access to the tunnel site.

Approximate sites of coffer dams in Middle Harbour

Government informs the community that usage of Spit Reserve West will not be impacted, yet the constructions will involve extensive noise and truck movements for an estimated 3 years of construction, severely impacting the amenity of the reserve, marinas, restaurants and surrounding residential areas of both the reserve and the tunnel site.


There is also significant risk to Middle Harbour from disturbance of sediment according to secret government documents leaked to the media. “Another underwater tunnel…connecting Northbridge to Seaforth could also create a plume of turbid contaminated water”(1).


When sediments are disturbed, devastating impacts could be forced upon the seagrass, aquatic life including endangered marine species such as the White’s seahorse(2), and people enjoying swimming, boating and fishing in the surrounding areas of the Spit, Clontarf, Beauty Point and Sailors Bay.


Other effects to tidal flows, sediment accumulation and aquatic life caused by the location of the tunnel tubes are unknown at this stage.


The particular design that has been selected is a cheaper option, with greater impacts upon residents and the environment. The tunnel could be built by tunnelling under the harbour the same as under land, eliminating the need for coffer dams and a construction site at Spit Reserve West entirely, but this design has been rejected by government.


The tunnel is a major construction project with significant negative impacts locally, and yet government estimates of traffic benefits are only a 15% reduction in traffic on the Spit Rd/Military Rd corridor (as estimated 63% of existing traffic comes from the Mosman area, versus 37% from the Northern Beaches).

1) Western Harbour tollway: what makes up the toxic sediment in Sydney Harbour (ABC News, March 14, 2018)

2) Endangered seahorses found on Sydney’s Northern Beaches during council repair work (ABC News, December 21, 2018)