“We really didn’t want to build a wall,” explains Bob Orth.
But Orth is one of 10 residents of Collaroy, on the beaches of northern Sydney, who each paid $ 300,000 to do just that.
And not just any wall. Construction began in December on a seven-meter-high raw concrete structure beneath residents’ properties, which overlooks a beach known for its dramatic erosion whenever there is a big storm.
Once the wall is complete, it will meander up to 1.3 km from the coast to the south of Narrabeen, consisting of a vertical concrete wall in parts and a liner – a sloping rock structure designed to absorb wave energy – in others. During its expected lifespan of 60 years, it will hold back the tides to protect 49 properties, 11 public areas, a rescue club and parking lot.
Residents, including Orth, will cover 80% of the cost, with the remainder paid for by the NSW Government and Northern Beaches Council.
“We didn’t want to invest $ 300,000,” says Orth. “But we had to build a wall and we did it strictly by the book.”
Collaroy is no stranger to storms – author Ruth Park sketched a living first-hand account of one when she lived in the area in 1945 – and the most famous one struck in 2016, when monstrous waves swept through the beach and washed away the shore, tearing a private pool from its moorings and leaving homes on the brink.
Over the next five years, in which two more storms hit the beach, residents of the worst-hit strip organized themselves by forming a company, contracting Horton Coastal Engineering to design a wall, and campaigning with success for board approval.
“Without the wall built here, we would be torn apart by the next storm,” says Orth. “I have no doubts in the world [that it will work], and no one has doubts here. The owners are very happy with the solution.
“Brutal engineering solution”
Others in Collaroy are far from happy. Brendan Donohoe of Surfrider Foundation is a local whose organization has been fighting against the construction of a dike for three decades. He says that by building the vertical wall, the council is sacrificing the beach to protect private property.
“The board was honestly shocked that we weren’t thrilled. We were really amazed at what they did, ”says Donohoe.
Because beaches are dynamic systems, changes in the physical environment – such as building on dunes or on the beach itself – can interrupt the natural processes by which sand moves, causing it to disappear from certain areas while accumulating in others.
Donohoe is concerned that the sand directly in front of the wall will be washed away in the next storm, and without a renovation program to artificially replace it, this section of beach will disappear for longer periods of time.
“At the end of the day, these properties are probably unprotectable,” he says. “Our beach is the thing we should be trying to secure – not in the monetary sense but in the sense of its continued existence.”
Angus Gordon, coastal engineer and former chief executive of Pittwater council, says vertical wall is a “brutal engineering solution” to a problem that would have been best solved by rock cladding.
“Basically, building an artificial cliff in front of the beach doesn’t match the environment,” says Gordon.
But Ray Brownlee, chief executive of the Northern Beaches council, dismisses the criticism, saying the wall’s design has been reviewed by a Danish coastal engineer, the Manly Hydraulics Laboratory and a team from the University of New South Wales.
He says the vertical wall has a smaller footprint on this section of beach than a rock coating would have had. When complete, two-thirds of the structure will be buried “most of the time,” he says.
“Council’s priority has always been to help residents protect their properties as long as there is no negative impact on the beach,” said Brownlee. “Our challenge, and the challenge facing Australia’s coastal areas, is to manage the impact of planning decisions made over a century ago. “
Climate change leads to coastal erosion
Collaroy and Narrabeen are certainly not the only Australian communities facing competing demands as climate change increasingly leads to coastal erosion.
Storms in late 2020 and mid-2021 wiped the sand off the main beach at Byron Bay in northern NSW, while a surf rescue club at Inverloch in Victoria was forced to shut down. withdraw twice from rising tides.
In Western Australia, storms hit Fremantle Harbor beach in 2019, leaving buildings on the verge of collapse, while Post Office Rock in Beachport, South Australia is recognized as one of the most popular beaches. most eroded from Australia.
Some 135 meters of land has been lost since 1946 along this part of Australia’s southern coast, with the ocean set to cross the dunes over the next decade and reclaim the Siloam Pool, a popular tourist destination.
Most of the time, this erosion occurs in remote places, but it is also increasingly affecting areas with high development.
A 2009 study by the then-Ministry of Climate Change and Energy Efficiency found that up to 247,600 homes were at risk of flooding if sea level rose 1.1 meters. A follow-up in 2011 identified thousands of additional commercial and industrial buildings that were vulnerable.
Some local councils, such as Fremantle in Western Australia, have adopted “managed retirement” policies, but often they have not been linked with buy-back programs to remove vulnerable homes without financially crippling homeowners.
State governments have been reluctant to step in, leading many homeowners to call for the construction of dikes to defend homes and businesses.
While these structures can temporarily stem the advance of the ocean, they sacrifice the beach for short-term safety.
“We are already paying it”
Since 1901, the world’s oceans have grown by an average of eight inches, but the effect has not been felt uniformly.
The reasons are complex and range from epoch changes in tectonic plates that cause one region to rise and fall in another, while human activity can make an area more prone to flooding.
Australia’s coastline has been relatively stable, according to Robbi Bishop-Taylor of Geoscience Australia, who helped create a tool that uses satellite data taken since the 1980s to map shoreline changes.
He says only 21% of Australia’s coastline has suffered erosion in the past three decades.
“The reason is often much more complicated than erosion or pure growth,” explains Bishop-Taylor.
Even in areas where the changes have been dramatic, erosion in one area can be offset by gains in others.
Bishop-Taylor says Point Stuart, a swampy area near Darwin, has lost about 500 meters in three decades, but this erosion has been offset by growth in the Gulf of Carpentaria, where land is growing at a rate of 10 meters per year.
However, climate change is increasing the rate of sea level rise.
According to the IPCC6 report published in August, people born in 1971 saw the world’s oceans rise at a rate of 1.9 mm per year. For people born after 2006, this rate has almost doubled.
Associate Professor Ruth Reef, of the School of Earth’s Atmosphere and Environment at Monash University, says these numbers may seem small, but typically a 1cm rise in the level of the sea leads to a decline of one meter from the coast on the beaches.
“The relationship is not individual because the beach is on a slope,” says Reef.
This process is exacerbated as climate change disrupts the normal wind pattern, altering the amount of energy that can cause waves, especially during storms.
“We still think of climate as something that’s going to happen, but it’s already happening,” Park says. “We’re already seeing an impact and we’re already paying the price – but we’ll see a lot more because sea levels are rising. “