Shaun Hollis, Yorke Peninsula Country Times
A ground-breaking study into the movement of coastal sand dunes paints a picture of what will likely happen to Yorke Peninsula’s extensive dune systems across coming decades, according to a leading global coastal studies expert.
Flinders University Professor Patrick Hesp said, as rising sea levels and less rainfall impact coastlines, dunes will increasingly migrate back from beaches and encroach on properties behind them.
“Certainly, farmers would be concerned about greater dune activity and losing some property,” Prof. Hesp said.
“The concern with declining rainfall patterns and then potential for greater dune mobility is there for the farming community.”
The findings come from an extensive case study of a long section of dunes on Younghusband Peninsula in the state’s South East, which Prof. Hesp said shows what to expect at some of YP’s more exposed beaches, including Ethel Beach, Berry Bay and Hardwicke Bay.
A section of the foreshore dunes at 42 Mile Crossing started eroding in the 1980s, causing a rapid acceleration of sand movement for the remaining dunes behind it.
Some of the dunes in the study have moved up to 100 metres further back from the beach, with the movement gathering momentum as their front sections are more rapidly eaten away by wind and waves.
“It’s a proxy for probably what will happen with sea-level rises along lots of sandy coasts in that, when you have shoreline erosion of this magnitude, it simulates, or is a proxy for, sea level rise doing much the same thing,” Prof. Hesp said.
“While we’re not seeing much effect of sea-level rise erosion yet, one would assume we’re going to get to some tipping point if it keeps going, and there’s every reason to think it will.”
Sea levels have risen about 30 centimetres in the past 120 years, but the rate of the rise is increasing.
The study has shown that, once the front section of any dune system erodes, wave action increasingly eats away at the shoreline and wind carries the sand further inland, where new dunes form at an average rate of nearly 2m per year, soon increasing beyond 3m a year.
“That’s equivalent to losing a tennis court from the front of your house every seven years,” Prof. Hesp said.
The dunes at 42 Mile Crossing are now marching inland at a rate of 10m a year, he said.
A new field of coastal dunes has developed in just over a decade, with the landward edge of the dunefield moving inland more than 100m in eight years.
Prof. Hesp said three factors may have caused shoreline erosion and dune evolution over the past 10 years: offshore reefs that would have protected the coastline are breaking down, the sea level is slowly rising and wave energy is increasing in the Southern Ocean.
“Such shoreline erosion and dunefield changes suggest what may happen in future to many Australian beach and dune systems as sea levels continue to rise with climate change,” he said.
“Once you’re up against this big older dune system and you scarp, or cliff, that, you end up with a 10 or 12m scarp, the wind accelerates that and then starts to cannibalise it, so you see much greater dune activity.”
He said sand dunes in areas such as Daly Head currently experience about a 3m per year migration inland.
“You would theorise that will increase.”
He said dune stabilisation techniques such as fencing and increasing vegetation do slow dune migration, but may not be feasible in remote dune systems.
“Where there’s significant infrastructure in the way you’ve got the same options you do on the Adelaide foreshore — you retreat, get the hell out of the way,” Prof. Hesp said.
“With dunes you then go and manually stabilise them.”
This article appeared in Yorke Peninsula Country Times, 23 April 2024.
