‘Managed retreat’: Should Australians withdraw from our beloved coastlines?

Experts are calling for a “managed retreat” from residential development on coastal areas as rising sea levels and climate change-fuelled storm surges increase the rate of erosion, jeopardising an estimated $25 billion worth of Australian property.

As global temperatures continue to rise, so, too, are our sea levels, playing havoc with our vanishing coastlines.

People take photographs of a garden swimming pool that was washed away from a property on the beachfront after heavy rain and storms at Collaroy on Sydney’s Northern Beaches in 2016.Credit: AAPIMAGE

Eminent coastal geomorphologist Professor David Kennedy, who has decades of experience studying coastlines, said Australians’ love affair with beachfront developments must change.

“We’re going to have to look at managed retreat,” he says. “We can’t keep building in the current hazard zone, let alone the future one. And we’re building more and more stuff in the current hazard zone.”

Property research group CoreLogic in 2022 estimated that $25 billion worth of Australian residential coastal property – 12,694 houses and 9441 units – were at high or very high risk from coastal exposure. Coastal erosion would have tangible effects on property valuations, home loan viability and insurance premiums, it said.

Australians’ love of coastlines – about 90 per cent of us live within 50 kilometres of the coast – has set us up with a conflict. Many of the most at-risk properties are legacy developments built on “fore-dunes”, or areas immediately behind beaches.

Groynes are effective at saving the beaches in Loch Sport.Credit: Jason South

A paper in the Australian Journal of Emergency Management argued that authorities must consider strategic planning to direct residential development away from high-risk beachfronts.

Bond University PhD student Mark Ellis, who co-authored the paper with associate professor of urban planning Dr Bhishna Bajracharya, said coastal communities would have two options as sea levels rose: retreat or adapt.

“When you adapt to it, you build [sea] walls, and that kind of creates a systemic problem and an ongoing one: it stops the house falling in the ocean but creates problems everywhere else.”

On Sydney’s Northern Beaches in Collaroy – which has been one of Australia’s most-studied coastal erosion sites – a swimming pool collapsed into the surf in 2016 during damaging storms that cost home owners and the state government $25 million.

The private seawall filled with sand with beach erosion below along the Collaroy beachfront.Credit: James Brickwood

After more ferocious storms in 2020, a controversial seven-metre concrete sea wall was installed to protect 49 private properties, a car park and a surf club.

But opinions differ on the value of sea walls in mitigating the worst effects of coastal erosion. Kennedy said the “rule of thumb” was that sea walls doubled the rate of erosion at either end of the wall.

“Really what a sea wall does is protect a property boundary,” he said. “So if the beach remains, that’s a bonus, but the primary reason for a sea wall is to protect whatever’s behind it.”

In 2021 the Intergovernmental Panel on Climate Change (IPCC) warned that sea levels could rise by 1.1 metres by 2100.

Lake Victoria is eating away at the shore in Loch Sport.Credit: Joe Armao

“Coastal areas will see continued sea level rise throughout the 21st century, contributing to more frequent and severe coastal flooding in low-lying areas and coastal erosion,” it said.

“Extreme sea level events that previously occurred once in 100 years could happen every year by the end of this century.”

Between 2014 and 2023, global sea levels rose by an average 0.48 centimetres per year, doubling the rate of sea level rises before 2002.

Former climate commissioner Lesley Hughes has welcomed UniSuper’s climate commitments but said more action is needed. Credit:

Emeritus Professor Lesley Hughes was a co-author of the fourth and fifth IPCC assessments, and told this masthead that the accelerating effects of climate change meant the sixth IPCC predictions – delivered just four years ago – could already be out of date.

“2024 was the world’s hottest year, and we seem to have seen a real uptick in both warming and in the melting of sea ice,” she said.

“The melting of polar ice in the Arctic and the Antarctic is a big contributor to sea level rise, as is the warmer water, so the climate models that we have been using, for example, by the IPCC, seem to be quite significantly underestimating climatic trends.”

Warming oceans magnified the impacts of storm surges on coastlines, Hughes said, and the east coast of Australia – home to the majority of the population and the majority of development – carried warmer waters than the rest of the country.

“We are a very vulnerable country as a whole to sea level rise, and we really need to do some serious planning for that.”

Erosion due to wild weather at Wamberal Beach on the Central Coast of NSW in 2020.Credit: Dominic Lorrimer

It’s not without precedent. After 12 people died when a three-metre “wall of water” swept through the Queensland town of Grantham, the Lockyer Valley Regional Council bought 378 hectares of land on which to build the new Grantham. After the federal and Queensland governments contributed $18 million in funding, hundreds now call the new town home.

Emeritus Professor Bruce Thom, an expert on coastal morphology who has advised successive NSW governments on coastal management for decades, did not support the calls for managed retreat, which he said would be prohibitively expensive.

However, he said authorities should be most concerned about new development in coastal systems in Victoria and NSW that operate as estuaries (with enclosed systems and tidal flows).

“The big issue for the future are in our estuaries: Sydney Harbour, Botany Bay, Port Phillip Bay, Western Port. These are the places where you’ve got massive, massive investments in the areas where sea levels are rising,” Thom said.

Erosion on Portsea beach, after the dredging of Port Phillip Bay in 2010.Credit: Paul Rovere

“And these are the places where the national interest is at stake. As sea level starts to rise 50cm to one metre above present sea levels, we got massive adjustments that have to be made, and this largely has to do with drainage efficiencies as well as inundation.”

The world’s oceans have absorbed more than 90 per cent of the heat generated by greenhouse gases since 1971. As the oceans warm, warmer water expands and sea ice melts, sea levels rise.

With higher seas and climate change come increased frequencies of storms and storm surges, and with both come coastal erosion.

In Victoria, the towns most affected by coastal erosion have been Loch Sport, in the Gippsland Lakes region, and Inverloch on the Bass Coast. CoreLogic has identified the Melbourne suburbs of Port Melbourne, Aspendale and Brighton as being particularly at risk, while in Sydney, Cronulla, Manly and Collaroy were at particular risk.

In August, UN Secretary-General Antonio Guterres said sea levels could eventually rise by 20 metres.

“Emerging science suggests that a two-degree temperature rise could potentially lead to the loss of almost all the Greenland ice sheet, and much of the west Antarctica ice sheet,” he told reporters in Tonga.

“That would mean condemning future generations to unstoppable sea level rise of up to 20 metres – over a period of millennia.”

When most people look at a house nestled above dunes on the beach edge, they see privilege and luxury. Kennedy, meanwhile, sees looming danger.

“Can we afford it at the individual level, but also can we afford it at a societal level?” he asks.

“If we [keep building there], we’re going to end up with ad hoc sea walls, which get larger and more expensive, and then they have to be maintained … and that’s an ongoing cost for future generations. But with sea levels rising, the cost will be going up exponentially.”

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