International
Coastal erosion at Cronulla Beach weeks after storms lashed the coast.CREDIT:BROOK MITCHELL

AUS - ‘These seas have stolen front yards’: Sydney beaches at risk of being washed away

Australian beaches could struggle to recover if a third La Nina weather event occurs this year, threatening coastal communities, experts warn.

Australian beaches could struggle to recover if a third La Nina weather event occurs this year after many of the most popular sandy stretches suffered back-to-back weather events that stripped away their sand.

As more extreme and intense weather events occur, once protected areas of beaches will become more exposed, threatening coastal communities, experts warn.

Dr Mitchell Harley, a senior lecturer at the University of NSW Water Research Laboratory, said Australian beaches are very dynamic and tend to fluctuate depending on the season. During storms, beaches lose more of their sand, while in warmer months beaches usually grow.

Beaches can take months to recover after an erosion event.
Beaches can take months to recover after an erosion event.CREDIT:BROOK MITCHELL

“We’ve been measuring Collaroy and Narrabeen beach for 46 years and, with those measurements, there have been fluctuations over a huge amount of space – up to 100 metres back and forth. The coastline is breathing in and out but when we look at long-term records they have generally been recently stable,” he said.

“During big storm events, like what we have seen over the past couple of years, what we see is that the waves strip the beaches of sand. It doesn’t disappear, it just moves into deeper water. The sand slowly returns to the beach during calming conditions.”

In normal summer months, waves move from a south or south-east direction. This typically means the northern end of the beach gets narrower and the southern ends get larger.

But during La Nina events, they shift slightly anti-clockwise and are more easterly, which leads to a higher risk of more erosion on the beach, particularly over the summer, and also “beach rotation” – where the beach realigns itself to the prevailing wind direction.

As a rule of thumb, it takes between five and ten days for every metre of sand from the shoreline to return to the beach, Harley said, and recovery can sometimes take months if beaches lose up to 40 metres of sand. But if there are back-to-back storm events, such as what has occurred over the past two years with La Nina, beaches may struggle to recover and begin to threaten infrastructure.

Read more.