Collapsing coast claims Collaroy. Again.

As Crikey reported at the end of January, Australia is collapsing around its edges.

Hundreds of beaches — and the communities, landscapes and infrastructure attached to them — are under imminent threat from accelerating erosion.

We reported that climate change, in the form of rising sea levels and more extreme weather events, was going to make this worse.

What we didn’t know at the time was that a case study was so close on the horizon.

Alongside the heavy rain in New South Wales over the past few days — which extinguished fires that had been raging in that state for nearly three months, just in case you weren’t already getting that “end of days” vibe — parts of the coast experienced a storm surge.

Foaming six-metre waves clawed away 25m from the Collaroy-Narrabeen beach, one of Australia’s worst erosion hot spots.

University of Sydney geoscience Professor Andrew Short told Crikey the narrowed beach would be more vulnerable now if there were another storm event before the beach had time to recover.

“The worst erosion always occurs when there are a series of such events, as it usually takes more than one storm to do severe damage,” he said.

Dr Mitchell Harley, a researcher who monitors Collaroy for the University of New South Wales, said there was potentially another storm coming next weekend which was “very concerning”.

Property owners in the area — subsidised by the Northern Beaches council with help from the state government — have spent millions of dollars on sea walls to protect houses in the area.

Short said these plans would not protect the beach.

“They have started building a seawall which will protect the houses but not the beach,” he said. “The only way to have a permanent beach is beach nourishment from the huge volumes of sand that lie in deep water directly off Narrabeen-Collaroy and, for that matter, much of the Sydney coast.”

Harley said the problem with nourishment was that it still had to be “topped up every few years”.

“So you’re locking in perpetual maintenance to keep the beach at a safe width,” he said.

Amazingly, it could have been much, much worse; back in 2016, the area lost 50m in a weekend. This time the waves weren’t as high, and the wind direction was different, which pushed the worst of the erosion away from the most vulnerable areas.