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-6pm weekdays and 8am-1pm Saturdays, plus night work where integration with existing roads and traffic management is needed – with associated road closures and delays. Tunnelling underground will be carried out 24 hours a day, 7 days a week. Whilst these are the standard construction hours, ultimately the hours are dependent upon the contractors doing the work, so significant of out-of-hours work could be undertaken.

Truck and vehicle movements

Noise, dust and traffic disruption from truck movements will have significant impacts on residential areas surrounding the sites. Heavy trucks carrying large machinery, concrete and spoil will travel on our roads, and queue to get in and out of the sites creating more congestion.

The EIS provides an estimate of the numbers of vehicles travelling to and from the sites in the region(3).



The total number of vehicles going in and out per day is over 3000, working out to be close to 1 large truck every minute from Balgowlah, or 4½ vehicles per minute across all sites.


Approximately every minute, a large truck carrying tunnel spoil will need to haul their load up the access road, uphill to Sydney Rd, outside Balgowlah Boys High School. This comes with heavy diesel exhaust, as well as trucks idling and creating queues to get in and out of the site.

Trucks will either carrying spoil south, further worsening traffic on Spit Rd and Military Rd, or travel west past Seaforth shops and along Frenchs Forest Rd – small local roads next to houses and with steep gradients that pose a danger to residents.

The EIS suggests that main intersections around the site would suffer longer delays, but that the traffic would be comparable overall because the road network has spare capacity. However the capacity on the roads depends upon when the trucks are on the road, and heavy delays are anticipated at busy times, unless construction vehicles can be forced to travel at less busy times.


The sites will also host a large number of workers; hundreds of people will arrive in the early hours and need parking for their own vehicles, potentially on local streets and residents have no authority to stop them. The Balgowlah site will also host workers that may be shuttle bussed to the Spit Reserve West site due to minimal parking being available.


Noise and vibration exposure

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. Some functions are excessively loud and the noise cannot be effectively mitigated by sheds or noise walls. Surface road construction cannot be covered and generally needs to be undertaken at night when traffic levels are low. Many residents will be impacted by construction noise as they are located on hills elevated above the site at Balgowlah, or simply too close to the work.


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


The EIS details many examples of the noise and vibration that residents will be exposed to from the various construction activities and construction times. These are detailed in Appendix G Noise and Vibration, Part 2. A list of relevant pages and examples of the maps are:

Balgowlah site maps – pages 25-29, 55-66, 102-108, 177-183, 206

Seaforth and Wakehurst Parkway site maps – pages 30-37, 67-76, 109-121, 184, 208

Middle Harbour and Spit Reserve West site maps – pages 15-24, 96-101



The number of homes estimated to be impacted by noise exceedance levels are below(4).



Only when TfNSW deems noise levels too loud and mitigations ineffective are residents eligible for at-property mitigation such as double glazing, or to be housed temporarily in hotels due to night noise exposure.

Some examples on these maps also include residences that are close enough they are within safe distances for vibration from machinery, and may suffer damage to their homes.



Dust exposure

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.

The EIS states that steps will be taken to minimise this exposure by, for example, covering all vehicles or hosing down trucks. These tasks are undertaken by the contractors on the project, and compliance needs to be enforced – many residents on similar projects have reported regular breaches of these type of requirements on construction sites.

Impacts of construction – Seaforth Bluff, 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 (63m x 25m on the surface – larger than an olympic sized swimming pool – and deep into the sediment) 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. A significant number of moorings will also need to be moved temporarily to allow access to the tunnel site.

Location of cofferdams on Middle Harbour and Backhoe dredge

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 5 years of construction, severely impacting the amenity of the reserve, marinas, restaurants and surrounding residential areas of both the reserve and the tunnel site.


The EIS states that noise from impact piling the cofferdam walls into the seabed will be so loud (over 75dB – a loud TV and greater), they will be restricted to 2 hours per day, drawing out the process to 12 months. The construction to sink and connect the tunnel tubes also involves loud construction activities, but must be done as one process for practical reasons that will take 24-48 hours at a time. The EIS states that “events related to crane/equipment/plant operation during tunnel unit immersion are predicted to be above the awakening reaction level”(5), so will involve noise exceedances enough to prohibit sleep for residents.



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).

The sediment is known to contain unsafe levels of heavy metals, lead, hydrocarbons, pesticides and other toxins. Sediment curtains will be used to attempt to restrict sediment spread during construction, but Bill Maher, professor of environmental chemistry and toxicology, has stated “I personally have never seen a sediment curtain that’s worked 100 per cent”.

This will mean that some sediment leaks are inevitable, and 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.


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 10% 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)

3) Beaches Link EIS, Appendix F Part 1, Table 5-3, Page 131

4) Beaches Link EIS, Chapter 10, Construction noise and vibration

5) Beaches Link EIS, Appendix G Part 1, Page XXXII