It's feared the sea walls protecting a strip of million-dollar homes on Sydney's northern beaches will collapse if more work isn't done to rebuild them.
The concerns come as a major sandbagging operation is under way in the beachside suburb of Collaroy.
Up to seven properties are teetering on the edge of collapse after huge waves and king tides lashed the NSW shoreline.
Metre-long walls protecting homes neighbouring the devastated patch of properties were "built in a hurry" following similarly ferocious storms between the 1960s and 1970s, coastal engineer Angus Gordon says.
"They were tentatively constructed and weren't all that well engineered," Mr Gordon said.
"So the existing sea walls are slumping and will need further work to make sure they stay standing," he said.
The risk of coastal erosion along the Collaroy and Narrabeen coastline has been well-documented for years, Mr Gordon told AAP.
But the issue of who pays to protect homes or repair current walls is contentious.
Northern Beaches Council general manager Mark Ferguson said attempts to extend the existing seawall were abandoned 10 years ago after more than 3000 residents protested against the plan.
"There's a conflict between people whose properties are affected and beach users, including surfers," Mr Gordon said.
Sea walls strip sand from the beach and can also have an effect on wave patterns, meaning surf-breaks are ruined.
Mr Gordon, who's worked on coastal engineering projects across Australia and internationally for the last 40 years, is in discussions with the Northern Beaches Council about a plan to build a so-called rock revetment wall.
"It's relatively easy to upgrade at a later date so it's particularly important when you're facing an uncertain climate future," he said.
The council is also working on a plan which would allow for a wall to be built with "beach nourishment" mechanisms in place.
"This would mean bringing in new sand to effectively rebuild the beach in front of the wall to offset the damaging effects of a seawall," Mr Gordon said.
"It's the right solution, albeit a fairly expensive one".
Seawalls cost between $100,000 to $200,000 per property to build, while sand replenishment costs are also hefty.
Planning Minister Rob Stokes in May announced an $83.6 million funding package for councils to address coastal risks and hazards, including beach erosion, coastal inundation and cliff instability.
The existing coastal zone management plan prepared by Northern Beaches Council recommends that a sea wall be constructed, a spokeswoman from Minister Stokes' office said on Tuesday.
"The council can apply for state funding towards works authorised in their coastal zone management plan," she said.
