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Beach erosion and big swell forecast for South Australia prompts warnings to stay away from beaches

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Beach erosion and extremely hazardous boating conditions are expected across most of the South Australian coast this weekend, with a massive swell prompting the Bureau of Meteorology (BOM) to warn people to stay away from affected cliffs and beaches.

A heavy swell of up to 10 metres in some parts of the state is expected to arrive Saturday evening and peak Sunday morning, although the Adelaide coastline and Mid-South Coast will be protected by Kangaroo Island.

BOM senior meteorologist Brett Gage said a series of intense low pressure systems passing well beneath Australia were going to send up significant wave heights of about 8 metres at SA’s wave buoy — Cape du Couedic off Kangaroo Island.

“With a south to south-westerly direction, the swell will push nicely up into the Victor Harbor and Goolwa area and, given that [area] might be quite busy with school holidays, that will be an area we’ll be very concerned about,” he said.

“We’re trying to let the public know that the surf on the ocean coasts will be quite hazardous, so it’s a good idea to stay away from the beach, or walking on cliff tops, and certainly don’t go out in a boat.

“All those sorts of activities are not a good idea for late Saturday through Sunday.”

The breaking waves in the area, which are currently forecast to be above 10 feet, will be impacted by onshore winds of up to 19 knots on Sunday that will ruin their potential for surfing.

Other breaks across the state will be similarly affected.

Spencer Gulf ‘dangerous’

The swell is expected to push up into the southern half of Spencer Gulf where Mr Gage warned people not to go out on the water with the exception of protected enclaves, such as Point Turton on Yorke Peninsula.

“It will be pretty dangerous for boaties out there,” he said.

BOM’s sea-level pressure analysis on Friday shows a strong low pressure system below SA.(

Supplied: bom.gov.au

)

Due to the swell’s direction, Mr Gage said it would not make it through Investigator Strait into the Gulf of St Vincent.

The state’s south east, however, is expected to cop the full brunt of the swell.

“I’m estimating a significant wave height Sunday morning just offshore from Robe at about 9 metres, but just that little further south, if you went 40 kilometres off Port Macdonnell, we could be getting wave heights of 10 metres down there,” he said.

On the shore, this could translate to breaking waves more than 15 feet high — accompanied by a strong onshore wind of 23 knots.

Maximum waves bigger

Significant wave height is a statistical definition calculated as the average height of the highest one-third of waves.

But BOM estimates that one in every 2,000 to 3,000 waves — or about three or four waves a day — can be about twice the height of the average wave.

“In some other states they have hazardous surf warnings,” Mr Gage said.

“We don’t have those here yet, and the good thing is most of SA’s infrastructure doesn’t get damaged by these events, but we might get significant beach erosion.”

Bobcat working to protect sand dunes at West Beach during storms
Beach erosion at affected beaches is expected as a result of the swell.(

ABC News: Malcolm Sutton

)

Mr Gage said it was likely the Kangaroo Island ferry would have to be moored on Sunday because the energy was likely to refract around its eastern tip as a 4-metre swell.

“That could be an issue for Kangaroo Island and I would say there’s every chance services won’t be running,” he said.

He said the swell was a one-in-one-year event, but it normally took place in the middle of winter when the strongest, deepest low-pressure systems were generated in the Southern Ocean.

“To get a one-in-one-year event in early April is really unusual,” Mr Gage said.

He said the highest significant wave height recorded at Cape du Couedic was about 10.7 metres.

The highest ever maximum wave height recorded at the buoy was 17.39 metres.

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