A section of Bermagui’s popular Long Swamp track was washed away in early July. Photo: Marion Williams.
Wild weather this year has highlighted the impact of coastal erosion on the Far South Coast.
In early July, part of Bermagui’s popular Long Swamp track washed away. With the track now closed to the public, volunteer group Bermagui Flora and Fauna Reserve Land Manager is remediating to save the precious wetland area by protecting the remaining hind dunes.
In April, flooding brought on renewed calls for action on coastal erosion affecting Surfside, a northern suburb of Batemans Bay.
Eurobodalla Shire Council’s coastal management plan to protect the shire’s northern beaches from coastal erosion and inundation proposes the construction of a coastal inundation levee – a raised embankment – to reduce the volume of seawater reaching low-lying areas at Surfside during large coastal storms. The plan identified beach nourishment, using sand from the Clyde River to replenish certain beaches.
Last month council began work on a new 250 m-long rock wall at Long Beach, Batemans Bay, after east coast lows caused erosion along much of the coastline and exposed the edge of Bay Road.
Region Group asked University of Wollongong Senior Professor Colin Murray-Wallace if there are any effective solutions to coastal erosion. His personal research interests are coastal environment changes over hundreds of thousands of years and modern sedimentary processes.
Dr Murray-Wallace said sandy coastlines were more susceptible to coastal erosion than rocky ones. Orientation, such as exposure to south easterly swells and incoming storms and waves, is another factor.
How much sediment is being brought into the area also has an impact. In the case of some Batemans Bay beaches, the Clyde River would play a role.
“We have had some wet years so there is potentially higher river discharge which may affect the local coastal environment with enhanced erosion possible,” he said.
In the case of beachside developments like Surfside, the rate of erosion would also be affected by how much vegetation was removed and if there were foredunes.
Schematic diagram of longshore drift dispersing sediment along a beach. Photo: Key Concepts in Geomorphology by P R Bierman and D R Montgomery.
Longshore drift is an important influence.
“It is the net movement of sand along the beaches of NSW,” Dr Murray-Wallace said.
“Over hundreds of thousands of years, sediment has gone from NSW to Queensland, so the sediment on Fraser Island and Moreton Island originated from NSW.”
With several Batemans Bay beaches being relatively open environments, there is potential for net loss of sand as opposed to horseshoe-shaped beaches where the sediment tends to remain and does not bypass the headland.
Dr Murray-Wallace outlined three approaches to slowing the impact of coastal erosion amid human-induced climate change and ongoing rising sea levels.
He said conceptually, “nourishing” a beach by replenishing with sand from elsewhere was a good approach. It would be an ongoing process that must be repeated regularly.
“Nourishing does allow natural beach processes to occur and is possibly a better solution than a hard structure,” he said. “Even rock wall structures can be undercut, undermined and ultimately fail.”
Groynes are another engineered hard solution. Unlike sea walls they are constructed perpendicularly from the ocean shore.
Dr Murray-Wallace said groynes slowed down the rate of sediment loss. Over time though, the sand builds up on one side of the groyne and ultimately bypasses it and moves to the next compartment.
The third solution is planting species such as mangroves, as has been done at the Wagonga Inlet Living Shoreline.
Some people have suggested moving towns away from the coastline to avoid the flooding and inundation problems that Surfside is facing.
“An extreme view is to let a new equilibrium get established,” Dr Murray-Wallace said. “I can understand that argument, but it isn’t a nice one.”
He said people would always want to live near the coast so a balanced, more nuanced approach was needed. He would like to see a coastal geomorphologist involved in any form of coastal development.
“If you can involve those experts in the design process of development, these situations of inappropriate development won’t occur,” Dr Murray-Wallace said.
“When you think of our use of landscapes, it is a small cost to have someone with that expertise to say no, build elsewhere. It really does need involvement of someone with understanding of modern coastal processes.”
