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More coastal erosion likely as low pressure system brings dangerous surf to east coast

By Kate Doyle, Tuesday July 28, 2020 - 12:23 EST
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Attempts are underway to stop further coastal erosion at Wamberal, after damage the previous weekend. - ABC

As parts of NSW sit teetering on the edge after last fortnight's storms, a low pressure system is bringing yet more dangerous surf to the east coast.

These destructive storm systems often come in a series of events and the impacts are only expected to get worse as the sea level rises.

So why do they do so much damage and what can we possibly do to combat coastal erosion?

Storm surge

'Storm surge' is the term used to describe is the increase in sea level as the result of a passing storm.

When this high water combines with high tide and ferocious waves it can spell disaster for our sandy dunes.

"A really strong storm surge usually comes at the same time with pretty large powerful waves because they're both generated by the same storm," University of Queensland geography lecturer Daniel Harris said.

"That increase in elevation allows for waves to reach higher levels on the beach and that leads to greater erosion into the dune systems."

If the surge comes on top of the high tide there is even greater damage.

Dr Harris said there was a list of familiar locations for coastal erosion events along the east coast.

Palm Beach, Kingscliff, Old Bar, Jimmy's Beach, Wamberal (which suffered so much damage in the last round of storms) and Narrabeen (with the infamous pool in the ocean incident back in 2016) are just a few well known erosion locations.

suffered from coastal erosion.

"Even places that are pretty well known like Manly, or where I'm from Cronulla have had some erosion issues as well," Dr Harris said.

Erosion can be a good thing

According to Dr Harris, dunes naturally moved in response to a storm event.

"Erosion isn't an issue if you don't have anything built near the coast," he said.

"The dunes get eroded and that sand is put in the surf zone, which protects the coastline by increasing wave breaking and taking the energy out of the waves that are coming to the coast.

"It's a very natural process. It's well known; we've known about it for decades."

Kathleen McInnes, leader of the climate extremes and projections group at the CSIRO, said it was a seasonal cycle.

"If there weren't buildings there, then during these stormy seasons you would get erosion of the back dune area and then during the calmer seasons of the year the more moderate waves actually transport the sand back onto the beach and build up those dunes again," Dr McInnes said.

"But the problem is that when the dune system is intersected by buildings it creates a situation where the coastline can't respond in a natural way to the natural forces that occur on a seasonal basis.

"Added to that, of course, we've got rising sea levels, which are pushing the area of impact further inland anyway.

"So that makes it an even worse situation."

What can we do about it?

Dr McInnes put it bluntly.

"There's no easy solution to protecting a sandy coast from coastal erosion," she said.

Putting in place hard structures like concrete or rock walls along the coastline could protect the dune, but Dr McInnes warned there could be consequences as a result of that protection.

"If we value our coastlines for their beaches, building seawalls, depending on how they are constructed, can actually accelerate the loss of the beach in front of it," she said.

"It might protect the buildings behind it, but you're not going to have a beach in front of it.

"It's quite a complex problem because you've got to understand what it is you're trying to protect, why, and what it is you may lose in the process of protecting it."

No-one wants to be at the end of the wall

According to Dr McInnes, the sea walls could also be problematic if you did not have a consistent approach along the entire coastline.

"One of the issues around when people try to protect their own properties is that they can make it worse for their neighbours," she said.

"This is why it can be quite a tricky problem to deal with, to try to get a solution that is a solution for everyone and doesn't benefit some and make other people experience even worse impacts."

The other major option for immediate protection is nourishment regimes, where the sand is manually replaced on eroded beaches.

One of the most well known nourishment regimes is currently in action on the Gold Coast.

But Dr Harris warned there were always long-term costs involved with both of these measures.

"One of the things that I would like to see more of are plans that are put together to have a fairly long-term view of how we're going to go with the beach system," he said.

"You want a continually functioning beach system; you don't want the coast to be concrete."

How to factor in the rising seas

Dr Harris said there had been a push in the geographical literature to stop seeing erosion itself being a problem, because erosion was the process that naturally allowed shorelines to move up in response to higher sea levels.

"The ideal approach of a lot of management is to try and get the coastline to be able to respond to these events without there being all the damage," he said.

"'Managed retreat' is the term that gets used a lot and it probably strikes terror into the hearts of people who are right near the ocean."

It's the process of removing infrastructure in locations of risk.

"But the idea is that, not now, but over decades, many decades, you'll slowly create a system that allows for some of that erosion to occur without it ending up getting houses."

The aim was that over longer-term timescales the natural movements of those shorelines would be able to return.

In the meantime, things like seawalls were being used to try to protect current infrastructure, according to Dr Harris.

"This is one of the questions that I wish I had the perfect answer for, but there probably isn't a perfect answer," he said.

"I live near the coast as well. There's a lot of emotion in play here."


© ABC 2020

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