“Protective works are a far preferable measure to a vertical seawall,” he said. “The community is not happy.”

Northern Beaches Council said there had been comprehensive community consultation about the council’s coastal zone management plan for Collaroy Beach.

Senior Lecturer at the UNSW Water Research Laboratory Mitchell Harley said many of the erosion issues that Collaroy faces stem from poor planning almost 100 years ago. Many other coastal communities face similar legacy issues, with councils in desperate need of greater support to address contentious issues, he said.

“There are a number of these places up and down the coast, and we are trying to solve issues that were put in place hundreds of years ago. The lesson from that is with climate change and sea level rises, there is an increase in pressures on the coasts,” he said.

“We will see more and more of these issues come up, and so the important thing is that we don’t create additional legacy issues by poor planning decisions that we make today.”

The La Nina weather pattern declared this week will add further pressure on many coastal communities, with cooler temperatures, rain and storm events likely to worsen erosion.

Dr Harley and his colleagues have been measuring the erosion on Collaroy for 45 years, and found it was usually worse during La Nina. The team will be monitoring the beach through newly installed instruments to observe how weather systems impacted on beaches and seawalls.

“Normally we get waves coming from the south or south-east. During La Niña events, they shift slightly anti-clockwise, so they are more easterly,” Dr Harley said.

This means there’s a higher risk of more erosion on the beach, particularly over the coming summer, and also “beach rotation” – where the beach realigns itself to the prevailing wind direction, he said. This typically means the northern end of the beach gets narrower and the southern ends get larger.

A report by the Insurance Council of Australia, released this month, estimates the Australian government will need to invest $30 billion in large scale coastal protection and adaptation projects over the next 50 years.

The projected figure represents just 1.2 per cent of the average yearly infrastructure spending by all local, state and federal governments. The report noted insurance cover for “actions of the sea” are generally not available and are further constrained due to the increasing risks from climate change.

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