Perth's Kwinana Freeway Will Be Permanently Flooded By 2100, Oceanographer Warns

ABC News - Emily Piesse

The report estimates the freeway will flood at least four times a year by 2050. (ABC TV)

Infrastructure likely to be affected by sea level rise: Kwinana Freeway Riverside Drive Langley Park Old Swan Brewery apartments WACA stadium Gloucester Park Maylands Peninsula Golf Course

Climate data modelling has found key infrastructure near Perth's Swan River, including part of the Kwinana Freeway, is at risk of permanent flooding by 2100 due to rising sea levels.
The study by University of Western Australia masters students examined data from the Intergovernmental Panel on Climate Change, and Fremantle tidal gauge records to predict what impact a rising sea level would have on the Swan River until 2150.
Professor of Coastal Oceanography at the UWA Oceans Institute Charitha Pattiaratchi said the most vulnerable areas for flooding were on reclaimed land — including Langley Park, Riverside Drive and Kwinana Freeway in South Perth.

"Most of the low-lying area around the Swan River is all reclaimed land. It didn't exist 100 years ago," Professor Pattiaratchi said.

Professor Pattiaratchi says areas of reclaimed land around the river are most at risk. (ABC News: Ben Tessler)

"If you actually go to the Supreme Court Gardens, there are rings where they used to tie ships."
The report said Fremantle's mean sea level was expected to rise 23 centimetres by 2050, and 83 centimetres by 2150, under a climate change model of medium severity.
However Professor Pattiaratchi said the Swan River water level could rise significantly by 2025, due to a peak in the 18.6-year lunar tidal cycle and the possibility of a La Nina weather system.
He said if the two events occurred simultaneously, the Swan River could rise by as much as 20 centimetres — which is more than the entire water level increase for the past century.
"What we are predicting to happen in 2050 can happen in the next eight years," he said.
The report estimates the Freeway will flood at least four times per year by 2050, with more frequent and severe storm surges exacerbating a steady increase in the mean sea level.
"By 2100, the Freeway will be underwater all the time," Prof Pattiaratchi said.

'We need to be looking at solutions'

Dr Kerry Trayler says Perth needs to look overseas for guidance. (ABC News: Emily Piesse)

Dr Kerry Trayler, who is the principal scientist in the Rivers and Estuaries Division of the Department of Biodiversity, Conservation and Attractions, said more frequent flood events in the Swan River would be caused by two trends.
One of these trends would be increasingly severe summer storms, causing upstream flooding, and the other, estuarine flooding from rising sea levels and storm surges.
"We need to be looking at solutions that are around the world. We're not dealing with this on our own," Dr Trayler said.
"There's a lot of places that are a lot more low-lying than us that are moving a lot more quickly than we are to look at this central problem, so we can learn from them, and I think that the beauty of the UWA report is it brings that into that local setting."
Dr Trayler said mitigation strategies could include retreat — moving key infrastructure away from the shoreline — or retractable walls next to the Freeway.

Main Roads considers rock barriers, river walls

The Swan River frequently sprays northbound traffic on the Kwinana Freeway during storms. (ABC TV)

In a statement, Main Roads said it was aware of the "potential future risks" posed by a rising sea level on the Como section of Kwinana Freeway and other road infrastructure.
The agency said a number of options were being considered as part of the Kwinana Freeway Foreshore and Infrastructure Protection Strategy, which covers the area from Mt Henry Bridge to Narrows Bridge.
The options include beach renourishment, rock barriers and river walls.
The UWA report proposes a much more significant investment — a storm surge barrage located at Fremantle Rail Bridge or Blackwall Reach — at a cost of between $185 million and $493 million.
The authors estimate the cost of the barrage would be recovered by 2030, and it would likely be closed 38 times a year to prevent flooding by 2050.
Professor Pattiaratchi said the storm surge barrier could be part of a broader discussion about mitigating flood risks.

"Are we just going to say, we'll just do some mitigations so that the Freeway is open, but some other areas will get flooded?," he said.

"It's a whole lot of policy decision-making which needs to be taken into account before you actually go to build a barrage."

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