Sea-level rise in La Niña complicates Western Australian beach movement

Oceanographers say growth and erosion in Australia’s west coast is intensifying in La Niña conditions, due to the stronger Lewin Current and rising sea levels.

Australia has experienced La Niña weather conditions for the past two years, and the Bureau of Meteorology announced this week that it will form again this summer.

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Sand dunes began to disappear at Moore Point in Geraldton during the winter of 2020.(ABC Midwest & Wheatbelt: Chris Lewis)

The Lewin Current, which flows south from the tropics, is stronger in La Niña, pushing more water against the coast, said Jeff Hansen, associate professor at the University of Washington’s Oceanic Institute.

“The Lewin Stream is weakest in summer and strongest in winter,” said Dr. Hansen.

Picture of sand dunes falling into the sea
Beach erosion on some beaches is normal, but a La Niña event can intensify sand movement.(ABC Midwest & Wheatbelt: Chris Lewis)

“With this seasonal difference in strength, we have about 20 cm of sea level higher in the winter than we do in the summer, and then when we have La Niña, add another 10 to 15 cm on top of that.”

Graghic image showing the different sea levels between the El Nino event and La Nina
The mean sea level anomaly in red shows the difference in sea levels between El Niño and La Niña.(Supplied: Advancement of Earth and Space)

It was the opposite, Dr. Hansen said, during El Niño, when sea levels dropped 10 to 15 centimeters.

CSIRO Oceanic and Atmospheric Senior Principal Investigator Ming Feng said La Niña will likely lead to more storm events that will increase coastal erosion.

“If we had a sea level rise of 1 cm, roughly 1 meter of coast would be affected,” said Dr. Feng.

Diagram showing the four major systems present across Australia
Eastern Australia, the Lewin River, the Antarctic Ocean, and the Indonesian are the four major currents in Australian waters.(Supplied: Commonwealth of Australia)

“For example, if we have a sea level rise of 10 cm, 10 meters of the coastline will be affected.

Profile picture of research scientist Ming Feng
Ming Feng says that La Niña will likely lead to more storm events.(Supplied: CSIRO)

“I think when you have a sea level rise, whether it’s a steady rise or during an extreme event, the shoreline is going to be more affected.”

Dr Feng said the ocean response to La Niña and El Niño weather phenomena has been a relatively new focus for researchers, aided by more comprehensive ocean monitoring systems that did not exist 20 years ago.

dynamic coastlines

Aerial shot of Sunset Beach in Geraldton and erosion happening
Local and state governments are concerned about Geraldton’s Sunset Beach erosion.(ABC Midwest & Wheatbelt: Chris Lewis)

Since 2020, the state government has spent $13 million trying to stabilize the Western Australian coast.

Geraldton and Banbury beaches have been hit hard by erosion this year.

In Geraldton, the Marine Rescue Building that had 50 meters of dune in front and in front of it is now less than 10 meters in front.

Aerial shot of a building near the ocean
The Geraldton Marine Rescue Building is located meters from the incoming sea.(ABC Midwest & Wheatbelt: Chris Lewis)

However, Dr. Hansen said monitoring part of the beach versus the entire coast is important.

While some beaches eroded, he said, others grew.

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Envision 32 years of rapid coastal growth in Twilight Cover, WA.(Source: Digital Earth Australia)

“Coastlines are a very dynamic landform, they act as a buffer between the ocean and land, and therefore they respond to the ever-changing ocean conditions,” said Dr. Hansen.

Profile picture of Assistant Professor Jeff Hansen
Coastlines are dynamic terrain, says Jeff Hansen. (Supplied: University of Western Australia)

“If you go to the beach every day, in most cases, the waves you see, the tidal level, will be a little different every day.

“And this constant change in ocean conditions means the beach is always changing.”

The ever-changing coastline of Australia can be seen on digital land australia map.

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Digital Earth Australia began collecting data on the coast of Australia in 1988.(Source: Digital Earth Australia)

Beaches move

Geoscience Australia Coastal Earth Watch scientist Robbie Bishop-Taylor uses satellite data every two weeks for the past 30 years to understand how coastlines have changed over time.

“The interesting thing that came out of this study, this product and research, is that when you zoom in to beach level in Australia, there is a huge amount of variability,” said Dr. Bishop Taylor.

Robbie Bishop Taylor's photo
Robbie Bishop Taylor watching coastal changes.(Supplied: Robbie Bishop Taylor)

“So you get beaches that are eroding very quickly, but then what you find is that you start to get smaller, and on the shore of a beach that is eroding very quickly, you will often find that the beach is growing at the same rate that the sand is slowly moving along the coast.

“I think people, when they hear about sea level rise, they kind of think every beach in Australia is going to be underwater and eroded everywhere, but climate change is running on top of local factors.”

Clint Duak's photo
Clint Duke says the public is more aware of erosion.(Supplied: Clint Duak)

Clint Duak is a Principal Coastal Engineer at MP Rogers and Associates.

“The beach is a very dynamic system and small changes can affect where the sand is,” said Mr. Duak.

“You can have flows of up to 100,000 cubic meters per year [of sand] It moves in one direction in summer and the other in winter, and if something interrupts the flow like a calmer summer and not a heavy breeze, it will let sand build up in some areas and erode in others.”

Dark storm shot from the ocean
During the La Niña event, the Leeuwin current grows stronger along the coast of WA.(ABC Midwest & Wheatbelt: Chris Lewis)

Mr Duke said there may have been a greater focus on erosion today, but no more areas have been eroded than when he began monitoring coastal changes 20 years ago.

‘I think the general focus on [erosion] It is much louder now through the media and is advertised more widely when there is a problem.”

“But I think the challenge for them is that local governments and coastal managers may now have a bigger challenge that they have to satisfy a number of different stakeholders within the community.”

Sunset shot in the water showing the sunset
The Leeuwin Current pushes warm waters from the north and lowers them to the south along the coast of Western Australia.(ABC Midwest & Wheatbelt: Chris Lewis)

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