Australia’s longest dune system stretches 190 kilometres from the mouth of the Murray River to South Australia’s south-east, part of the thin strip of coastline that separates the wetlands of the Coorong from the crashing waves of the Southern Ocean.
The coastline here is rugged, remote and beautiful, accessible only to the lucky few who can come in by 4WD and boat.
It’s also eroding and changing at an alarming and accelerating rate, which scientists say should be a lesson for coastal communities around the country as they prepare for the effects of sea-level rise.
Flinders University professor Patrick Hesp first came to the area around 42 Mile Crossing, near Salt Creek, in the 1970s as a young PhD student.
He returned in 2013 as a world expert in coastal-dune geomorphology and was shocked to see the amount of change that had taken place.
“In 1978, when I drove along here you had 100 metres more of beach and dunes with a 60m-wide foredune. Entirely gone now,” he said.
With PhD student Marcio DaSilva he began to visit regularly and examine historical photographs and satellite data.
“Every few months we come, two or three months and it’s gone more, and the dunes are rapidly, massively changing,” he said.
They found that an initial rate of erosion of 1 to 1.5m per year in the 1990s had accelerated and is currently 3.5m per year.
As the beach disappears the foredunes become cliffs and collapse and the sand is moved over those behind, smothering vegetation and destabilising them.
“In the last 10 years or less, a new dune field has developed that’s gone up to 200m wide across the older dune system and continuing to expand landwards,” Professor Hesp said, adding that the erosion sites were also becoming wider.
The dramatic changes here are thought to be due to a combination of increasing wave power in the Southern Ocean, a rise in sea levels, and breaking down of an offshore limestone reef that once absorbed the power of the waves before they crashed onto the coast.
Professor Hesp said if the major shoreline erosion he was seeing in the Coorong started to be seen elsewhere, Australian coastal communities could see “remarkable change” and would need to consider how to protect their assets.
“Especially where you’ve got decent dune systems. They’re extremely good at translating upwards and landwards with sea-level rise and erosion but if you’ve got infrastructure in the way then there’s going to be huge problems,” he said.