Toxic fumes will be trapped over Balgowlah and neighbouring suburbs if the State Government goes ahead with its existing plans for the Northern Beaches tunnel.
That’s the view of a community group which has carried out a detailed assessment of the Beaches Link tunnel plans, focusing on the location of vehicle access points and exhaust stacks.
The plans, which were leaked from the RMS and published in the ABC and Sydney Morning Herald earlier this year, show two access points for the Northern Beaches - one near Serpentine Parade and Burnt Bridge Deviation, Balgowlah and the other on Wakehurst Parkway, near Kirkwood St, North Seaforth.
The Seaforth/North Balgowlah Beaches Link Community Group says both locations are problematic.
Group spokesperson Marco Corrent says the group wasn’t trying to stop the Beaches Link project, but simply to get community input into the design process.
“We just need some open thinking from the government," he said. "And the integration of some of our ideas into their designs, because that is what the community wants."
“We’ve put together a document, with advice from a commercial architect, civil engineers with state infrastructure experience, ventilation engineers and other experts. It points out the problems with the existing plan and suggests cost-neutral alternatives.”
The document, which has been sent to the RMS and to State Roads Minister Melinda Pavey, identifies the Balgowlah ventilation stack as particularly worrying.
Not only is this stack less than 150m from Seaforth Primary School, but it’s located in a topographical low point that is notorious among locals for trapping smoke and other emissions.
This occurs as the prevailing easterlies from the ocean stop smoke or fumes from dissipating out to sea, but are not strong enough to blow them over Seaforth Ridge, immediately to the west. Emissions from an exhaust stack would therefore build up over Balgowlah, gradually spreading out over the "valley" that extends from Manly to Brookvale and North Curl Curl - a densely populated area with at least 12 schools and many kindergartens and day care centres.
While the Balgowlah location is too low, the group believes the Seaforth location is too high for an access point so close to the deep tunnel section under Middle Harbour.
Their assessment reveals that the grade from the tunnel low point to the proposed exit at Seaforth is 4.5%, which exceeds the RMS own guidelines and is likely to cause excessive pollution as vehicles drop into low gear to tackle the climb.
As well both locations are close to existing houses and near precious bushland.
But solutions are possible.
One idea is to shorten the Balgowlah tunnel spur - the section between the main tunnel and the Balgowlah exit - to 500m, a length at which it would not need its own exhaust stack. All the exhaust emissions would then be safely vented at the Seaforth Exhaust Stack, located on a high, windy ridge.
And the Seaforth access portal should be moved 600m further north along the Wakehurst Parkway resulting in a longer distance for the climb from the tunnel low point and therefore a gentler, safer grade.
The document says these relocations would also mean fewer homes would be affected in both locations, meaning the government would save money on house acquisitions and on expensive noise mitigation work, as well as causing less disruption to the community.
Mr Corrent said the group has been told the project is only in the concept stage and that their ideas will be considered for the final design, which will be made public next year.
"I'm hopeful they will take our ideas on board," he said. "This is what the community wants. People are being polite now - but they won't put up with having an exhaust stack right next to a primary school.
"We have a lot of support, including from Manly Ward councillors (Deputy Mayor) Candy Bingham and Sarah Grattan, and from (Northern Beaches Council Mayor) Michael Regan."
The Beaches Link assessment document is available here:
Candy Bingham, Deputy Mayor, Northern Beaches Council. Background in marketing, public relations & community engagement. Author of five business books. Former Lady Mayoress of Sydney. Aka Candy Tymson.