Sydney coastline “dodged a bullet” with bombogenesis, threat of coastal erosion still looms

After a week of serious predictions and preparation, it seems we’ve reached the end of the severe low pressure system hitting NSW, with rain ceasing and the sun returning. For our coastline, however, the damage is still being measured. 

The Lorikeet chatted to coastal erosion expert Associate Professor Mitchell Harley, from the University of New South Wales, about what this storm showed us, and what we have to come.

North Shore Lorikeet: How significant was the coastal erosion caused by this most recent storm?

Mitchell said that, for most of coastal New South Wales, the weather event hasn’t fully concluded. 

“They’re still mopping up the impact, because while the storm disappears, the waves are generally the last thing that remain.

“But from the assessments, it looks like to an extent, we've dodged a bullet.

“The original forecast had the cyclone a bit further north, more intense as well, and that was a huge concern for areas on the central coast of New South Wales, places like Wamberal and The Entrance North. From when we had big storms back in April, there are already houses which are really in a vulnerable position.”

Are we already at the point where there's a strong concern about houses being swept into the ocean or severely damaged?

“Yeah, at the moment, they're in a very vulnerable position. And there's certainly a risk of houses potentially being undermined and collapsing onto the coastline.”

Generally, are Sydney beaches adequately equipped to endure weather events like this?

“Typically, yes, except for the known erosion hotspots. … Colloroy and Narrabeen are obviously one, Bilgola Beach, for instance, and Mona Vale basin. These areas are just the hotspots.

“[There’s] nothing peculiar about the beaches per se, but simply because poor planning in the past has meant that they've been built far too close to the active coastal zone.”

In these areas where there's serious concerns of erosion, what do we really need to endure future weather events like this, that might be even more severe?

“The first thing is strong planning policy to ensure that we are not repeating the mistakes of the past, putting more and more assets close to the coast. Already we're seeing — despite the known threat — increased infrastructure in the active zone, right?

“That's a huge issue going forwards, where we continue to repeat planning mistakes and not consider, firstly, the natural fluctuations and the hazards that are already existing, but also the future ones, with sea level rise and climate change.”

Sea level rise and climate change

According to the Intergovernmental Panel on Climate Change, the global mean sea level “continues to rise at an accelerating rate” due to human-generated climate change. In 2017, a NSW-wide assessment into coastal erosion found that this projected acceleration in sea level rise is expected to increase the impacts of coastal erosion caused by storms.

“And look, there's no one size fits all,” said Harley. “It's all a question of the unique local conditions. But obviously what's called nature-based solutions where appropriate, so things like soft engineering approaches, where you can nourish the beach with sand and grow naturally, that can be an option.

“As a last resort, sea walls are very effective at stopping erosion, but that needs balance. It needs to balance the interests of all parties, right? And it's a very contentious issue.”

Some groups, such as SurfRider, have had criticism of seawalls in the sense that they help to protect properties to a certain point, but beyond that, they worsen erosion. Is that something that happens?

“It's a gray area about whether seawalls actively enhance erosion. It's an area of active study … but certainly, if you put them too close to the coastline, you're basically restricting the natural sand buffer, so that it can, in times of erosion, completely cut off the beach. 

“You can see that sometimes in Colloroy/Narrabeen, where the seawall is quite close to the active zone, and during these times it can completely restrict beach access.”

Has the installation of artificial reefs been considered as a strategy?

“That's an appropriate solution in some coastal environments. It's a lot more challenging in Sydney. The continental shelf in Sydney gets deep very quickly. It's not a shallow continental shelf where typically these types of approaches work or have been implemented.”

While it seems that, largely, Sydney was spared the worst of this weather event, the effects it has had on our coastlines give serious indication of what we need to prepare for in a worst case scenario. 

A Griffith University report published earlier this year forecast worsening flooding events and less frequent, but more intense storms as a result of sea level rise.

Image credit: Bureau of Meteorology, Narrabeen-Collaroy sea wall image courtesy of Rowan Hanley, Unsplash