The Wicked Problem of the Collaroy Seawall
“It’s a wicked problem they’ve got, in the true sense of the word.”
So says Brendan Donohoe of the conundrum facing Northern Beaches Council in relation to the Collaroy beachfront. Donohoe has presided over the Northern Beaches branch of the Surfrider Foundation for over twenty years, and he’s currently livid with the council.
The reason is the appearance of a concrete seawall along a stretch of beach between Wetherill Street and Stuart Street, which both run off busy Pittwater Road. The area has been slowly receding due to storm damage - there’s evidence of erosion dating back to the 1920s - while at the same time being intensely researched by coastal geographers.
It’s also been the focus point for opposition to coastal development; an abject lesson about what results from bad policy. The lessons, it would seem, are still being learnt.
“I saw the construction going in,” says Donohoe of seeing the area cordoned off earlier this year, “and thought they were building rock revetments. Angus Gordon, an engineer with fifty years experience in coastal engineering, assumed the same.
“My understanding was that council were looking at a rock revetment as they'd given approvals to a couple of other DAs for rock revetments,” says Gordon.
Both Donohoe and Gorden were correct, up to a point: The construction began with concrete piles sunk six metres below sea level, protected by a rock toe. However, the work then continued skyward with a seven metre vertical concrete wall on top of the foundations.
The finished work is 100 metres long by 13 metres high. The seven metres protruding above sea level is vertical, even going beyond vertical for the final metre to prevent wave overtopping.
“It’s brutalist engineering,” says Gordon frankly. “It’s like stepping forty years back in time. We’ve long known that putting a hard structure...particularly a hard, vertical structure, on the beach increases erosion.”
Both Brendan Donohoe and Angus Gordon, and other people Swellnet spoke to, admit to being blindsided by the construction. They can be excused as they thought they’d be informed before any such works took place, as per the 2016 Coastal Management Act.
The Act was introduced by Rob Stokes, the NSW Minister for Planning and member for Pittwater. Among many objectives, it outlines how people living in threatened property might defend their homes. It also enshrines a process of community consultation before a council adopts any coastal programs.
At this point, no-one can say if any consultation occurred, though the cynical view is council ticked the box by distributing flyers to the immediate neighbours, all of whom would want similar works built to protect their properties.
“I get informed about a proposed bike lane two suburbs away,” questions an aghast Donohoe, “but I hear nothing about construction abutting a nearby public beach?”
Gordon was equally puzzled: “I guess people become frustrated with the bureaucratic process and find ways of not involving the public. The legacy of that approach will be something future generations will have to live with.”
The concern about the seawall stems from the dynamic nature of sand dunes and how introducing a hard structure onto the foredune interferes with the natural state of flux. During periods of low swell energy, sand accumulates on the beach, widening the profile and forming a natural barrier for when storms and large waves erode the coastline.
The process is cyclical, however short-sighted development upon the foredune, built during times of a wide beach profile, impedes the system. Rather than a natural ebb and flow of wave energy, a hard structure increases reflective energy and turbulence, making it difficult for sand to settle and accrete. Beaches with hard structures can return, though it takes longer, and rocks and concrete in the wave zone also make for a dangerous combination.
An increase in storm activity - particularly from the east and north-east, as has been proposed by Associate Professor Ian Goodwin - and the looming threat of sea level rise are X-factors for East Coast beachfront development.
Collaroy has a long history of property erosion, yet a century after it was first documented there’s no consensus about how it should be managed. In the early 2000s, Warringah Council (as it was then known, it’s since been amalgamated with Manly and Pittwater) spent $6 million dollars buying three properties. Though with 80 properties at risk, and coastal real estate prices at a premium, they gave up on that approach in 2007.
In a 2007 story for the Sydney Morning Herald, both Rob Stokes and a spokesperson for Warringah Council admit buyback isn’t feasible and that other means of defence would be necessary, such as dune reconstruction, revegetation, and sand nourishment. Seawall construction isn’t mentioned.
Perhaps the omission was because in 2002, protestors, led by Brendan Donohoe and Surfrider Foundation founder Tom Kirsop, formed a “line in the sand” stretching from Collaroy to Narrabeen opposing the construction of any seawalls. The activism of Tom Kirsop is legendary and in December 2019 Northern Beaches Council honoured him with a park at Narrabeen called Surfrider Gardens.
At the opening, Mayor Michael Regan spoke fondly of Tom’s achievements crediting him with “adding swathes of precious coastal habitat for protection for future generations.” The Mayor also unveiled a plaque that mentioned the “line in the sand” protest.
However, there’s an irony that could've been lifted straight out of a script for Utopia. While celebrating his record for coastal protection with a park on the Collaroy-Narrabeen stretch, Northern Beaches council was also processing a Development Application that’d threaten the very same beach. Records show the DA for the Collaroy Seawall had been lodged 18 months earlier in July 2018.
Of the people that Swellnet spoke to, the opinions of how we got to this point swung from nefarious (“It was rushed through during COVID because they knew people were occupied”) to inept (“It was signed off by a mid-level planner with no knowledge of coastal processes”). What they could all agree upon is that council has lost the trust of all who’ve opposed the seawall over the decades.
“The properties were bought in good faith,” said one local who wished to remain anonymous, “and the owners must feel an obligation for the authorities to protect them, but a seawall is last century thinking.”
In 2017, Gold Coast City Council funded, in conjunction with threatened property owners, an artificial reef offshore from Palm Beach. The theory is that the waves break further offshore, soaking up wave energy that would otherwise erode the leeshore dune system during storms. Though still in its early days, the reef - which cost $18 million - has maintained beach width since it was completed in 2019.
The idea has never been proposed for Collaroy. Instead, sand nourishment is the popular solution to maintaining beach width, though both Donohoe and Gordon are feeling ‘once bitten’ and skeptical of any council promises.
“It would be possible to introduce a major sand nourishment program to move the shoreline seaward,” says Gordon. “The Local Government Act allows the council to set a special rate to pay for that.” Moreover, the current DA makes no mention of sand nourishment from sand sourced elsewhere, such as deeper water offshore. Instead they provide a caveat for bulldozing sand from low on the beach to higher on the beach in times of heightened storm activity - which only lowers the beach’s natural defence system.
In a story on Northern Beaches Review, Bob Orth, who lives in one of the houses behind the seawall, said the seawall should inspire others to do likewise.
"Once this is up it'll be a momentum for others to do it too," said Orth. Meanwhile, those on the other side of the divide are fearing the precedent of a return to hard structures and what this might mean for the rest of the Collaroy and Narrabeen beachfront, not to mention Wamberal, Old Bar, Byron Bay, and any other area where bad planning policy has created a wicked problem.