Sand dunes lining Australia’s longest beach are marching inland the width of a tennis court each year, due to rapid erosion triggered by the heightened lapping of the Southern Ocean.
Measurements painstakingly gathered by Flinders University scientists reveal a central section of shoreline along South Australia’s Younghusband Peninsula is disappearing at a rate of 3.3 metres annually.
More alarming, sand exposed to the wind as the beach is carved open is retreating from the waves at 10 metres per year. In its path is the iconic Coorong.
Some 180 kilometres southwest of Adelaide, the Ramsar-listed wetlands extend to the mouth of the mighty Murray River. On the land of the Ngarrindjeri people, they were the setting for Australia’s much-loved children’s story, Storm Boy.
The network of critically endangered coastal lagoons is home to Australia’s largest pelican rookery and a menagerie of exotic birdlife including pied oystercatchers, red-necked avocets, rapidly vanishing orange-bellied parrots and the furtive Australasian bittern.
If the creeping dunes keep on, the future of the unique stretch of wilderness will be imperilled, according Flinders’ environmental science head Patrick Hesp.
Yet it’s happening within plain sight and in the geological blink of an eye.
“This is an extraordinary rate of development and, if the shoreline erosion trend continues to expand north and south as it appears to be, it will dramatically change the national park dune system,” Professor Hesp said.
“And it may also significantly impact the Coorong Lagoon as dune sands invade it.”
Within the 190 kilometres long peninsula, at 42 Mile Crossing, a major shoreline erosion phase is in train.
This coastal barrier was largely barren in the 1940s but gradually changed as rabbits and domestic animal grazing were removed. Even so, the shoreline has eroded 100 metres since 1980 at an average rate of 1.9 metres per year, Prof Hesp said.
A new dunefield took less than five years to develop and has since extended landwards more than 100 metres in eight years.
“We tend to think of most dune formation phases having developed over a long period of time but our research has shown the opposite to be true on the Younghusband Peninsula,” according to Dr. Marcio DaSilva who wrote his PhD on the subject.
“We are witnessing the evolutionary trajectory of that coastal sand sheet as it responds to sustained erosion and the dune sheet transitions to a dunefield.”
While several hypotheses have been forwarded to explain what has happened, the few proven factors include increasing ocean wind speeds and wave heights.
Prof Hesp said the sea has been rising for more than a century, while wave energy has increased notably in the past decade. Offshore reefs that would have protected the coast have also been disintegrating.
He said the findings are a call to action for increased research on coastal processes and particularly relationships between sea level rise, future climate change and the response of coastal dune systems.
“This study provides direct evidence shoreline erosion and subsequent cannibalisation of a formerly vegetated dunefield has produced a new transgressive dune field at an extremely rapid rate and in less than a decade,” he said.
“It’s the proof there is cause for alarm.”
