When a cyclone hits this far south, history shows flooding is the biggest risk
By Mike Foley
Tropical cyclones conjure images of tornado-like winds ripping roofs from houses, uprooting trees, tearing boats from their moorings and blowing in windows and doors.
But history shows that the biggest threat from the weather system is the possible flooding that will hit after the cyclone breaks down.
Residents in south-east Queensland and northern New South Wales are on high alert, waiting to see where Tropical Cyclone Alfred may cross the coastline this week.
However, the worst damage could come when the weather system becomes an ex-tropical cyclone – a huge, slow-moving storm system that causes widespread flooding.
The Bureau of Meteorology said up to 400 millimetres of rain could fall in some locations on a single day on Thursday or Friday.
Natural Hazards Research Australia chief executive Andrew Gissing said it was possible that an ex-tropical cyclone could emerge from Alfred, causing major flooding.
He likened the potential inundation to the flooding caused by Cyclone Zoe that hit the NSW-Queensland border in 1974 and the Great Gold Coast Cyclone in 1954.
“We’ve got flood watches out for moderate to major flooding from the Sunshine Coast down to Port Macquarie and there’s the other aspects of the cyclone too, with strong wind and coastal erosion,” Gissing said.
“The previous category 2 cyclones in 1974 and 1954 caused significant flooding across all those regions.
“We’ll only know in hindsight, but this could be another one.”
Ex-tropical cyclone Debbie caused widespread flooding in Brisbane in 2017.Credit: Glenn Hunt
Two cyclones have crossed the coastline at the NSW-Queensland border in the past century, causing major flooding in Brisbane and on the Gold Coast, and hundreds of kilometres south into NSW at Lismore and further to Coffs Harbour.
Cyclone Zoe was the most recent system to cross the coast, landing at Tweed Heads in March 1974 and causing flooding from Brisbane to Coffs Harbour. Around 200 people were evacuated from Murwillumbah, and 500 families were evacuated from Lismore.
In February 1954, the Great Gold Coast Cyclone hit near the NSW-Queensland border. The Bureau of Meteorology reported between 26 and 30 people died as a result of the severe winds, storm surges and flooding from Brisbane to Grafton in NSW, with rain up to 900 millimetres in some locations.
The most recent major flooding in northern NSW and Brisbane in 2022 resulted not from an ex-tropical cyclone but a slow-moving east coast, low-pressure system.
Brisbane’s devastating 2022 floods: Two residents use a boat to save items from their home in Auchenflower.Credit: Peter Wallis
Ex-tropical cyclone Oswald delivered torrential rain that isolated parts of Queensland and the northern rivers area of NSW in March 2013.
Seven people died, including a three-year-old boy, who was hit by a falling gum tree while watching the floodwater rise from the Kedron Brook bikeway in Brisbane’s north with his parents.
Gissing said flooding posed the greatest risk to life. Most lives were lost, he said, after people chose to enter floodwater.
“Flooding is the deadliest facet of a cyclone. Only a small error in judgement can be fatal,” he said.
“Previous research has found that 84 per cent of motorists ignore road closure signs. Those that are most likely to enter floodwater are younger men, those that work outdoors and drivers of 4WDs.
“It might be deeper or faster flowing than thought, the road beneath could be washed out, or conditions may rapidly change. Remember, if it is flooded, forget it.“
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