The seawall protecting the Gold Coast from Tropical Cyclone Alfred

With Tropical Cyclone Alfred approaching, the Gold Coast’s decades-old hidden rock wall acts as the city’s line of defence against a surging ocean, according to an engineering expert.

For about 50 years, the Queensland government has had a policy that meant seawalls must be constructed along the “A-Line”.

The decision came after severe storm erosion in the 1960s and 1970s. The seawalls were constructed to protect coastal infrastructure from erosion.

The Gold Coast has been buffeted by Tropical Cyclone Alfred, which is slowly moving towards the south-east Queensland and northern NSW coasts.

The southern end of the Gold Coast, Coolangatta, has already felt the force of the cyclone winds, recording gusts of up to 100kph on Thursday night.

Gold Coast City Council acting mayor Donna Gates said one of the major concerns was the significant erosion along the beaches.

“There’s extreme erosion between the Southport Surf Lifesaving Club and Narrow Neck, and the council engineers are actually assessing the damage at the moment,” she said.

How Gold Coast built resilience on its coastline

Engineer Michael Bale, from Michael Bale & Associates, says the requirement for all new developments on the Gold Coast’s coastline is to be protected by a seawall.

The local council, he said, had built seawalls in front of public land.

“All of the private developments that have been constructed sort of since the 70s, it’s a requirement that they have to build a wall on this line,” he said.

“It’s a foreshore seawall that’s essentially 5 metres thick, and it extends down underneath the sand dune.”

According to the Gold Coast City Council, there are about 14 kilometres of public urban shoreline and nine kilometres of private urban property that require seawall protection.

The properties that did not have seawall protection were often older, near Palm Beach and the southern areas of the Gold Coast, Mr Bale said.

He said those properties were likely built before the A-Line was established about 50 years ago.

“If the rock wall is not there, then they’re basically at the mercy of having to put sandbags or something down temporarily to try and stop that erosion.”

Gold Coast City Council has made both the construction and maintenance of the seawall on private property the responsibility of the owner.

The council’s city plan sets out that before any development or redevelopment of beachfront properties occurs, a seawall is required.

“It’s a requirement of the city planning condition that you have to construct [a seawall] on that same alignment [as the A-Line] so that as they all get built and joined together, they’ll end up being a foreshore barrier that essentially protects from waves and erosion,” he said.

“So once the sand gets ripped away, the rocks are protecting the properties behind. So the waves could go over the top, but a little bit, but at the end of the day, it stopped the erosion.

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Five decades of building

The construction of the seawalls along the coastline of the city has been happening for about 50 years.

It’s a policy that Mr Bale believes has strengthened the city’s resilience.

Additionally to the construction of a seawall, he explained, there were also requirements on how developers built the foundations of properties along the coastline.

“How deep the foundations the properties that are being constructed have to be, to make sure they’re designed for this beach scour and erosion,” he said.

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