Coastal Heritage and Sea Level Rise

The Aboriginal middens that dot our coast are a valuable part of Australia’s heritage. Many are nearly as old as the current coastline – that is 4000 to 5000 years old – compared with which the European occupation of the last 250 years pales into insignificance. These middens, often identified as clear bands of charcoal and shells, are vulnerable to sea level rise and coastal erosion. One midden with which I am familiar, is located at the Red Bluff near Lake Tyers.

I have been visiting this site on a regular basis since 1986. Since that time the sea level has risen by about 100mm and the coast is gradually being eroded – perhaps having retreated by two or more metres during that time. In the short term it is coastal erosion and storm damage that is having the most effect on this midden and severe erosion of primary dunes is clearly visible in nearby parts of the coast.

Bruun’s rule states that the coast will retreat 50 to 100 times the vertical rise in sea level. Here the figure seems more like 20 to 30 although other parts of the coast with which I am not familiar may be retreating more rapidly. Another aspect of this is that sand and soil from the eroding coastline must be deposited somewhere – either back off the coastline making the sea shallower or moved along the coast and deposited elsewhere. The situation at Inverloch seems to be a case in point where severe and rapid erosion has occurred in front of the surf lifesaving club and much of the sands deposited in Andersons Inlet.

About the end of the 20th century the Red Bluff midden was fenced off from the public – but not the ocean. All that remains are the posts and a single wire – the erosion has continued well beyond the fence. About three years ago (pre covid?) the west end of the midden was shored up with sand bags (image above). Although this appears to be holding – the distinct lines of the midden are no longer visible – and high tides and storms appear to be continuing their slow but enveloping progress.

It seems almost inevitable the Red Bluff midden will eventually be lost to the sea in the not too distant future. Measures like sandbagging are short term and may be ineffectual. Perhaps it is time to start planning for an archaeological excavation of this site – and others like it – as part of a comprehensive program of adaption to just one of the many effects of a warming planet.