This stretch of northern New South Wales and southern Queensland had not seen such a thing in most people’s living memory – not since an unnamed cyclone hit the coast at Coolangatta on the night of 20 February 1954.
Wind gusts of 100 km an hour tore through Brisbane that evening, while floods reached two metres at Kirra, Queensland, and the Richmond River expanded to a width of 11 km in Lismore, New South Wales. The storm took up to 30 lives.
The tropical cyclone the Bureau of Meteorology warned would hit the same region 71 years later – this past March – was tipped to be even more devastating. Queensland stocked up on sandbags, the NRL and the AFL cancelled games, and schools and universities called off classes. Reportedly, Prime Minister Anthony Albanese postponed his planned date for the Federal Election to not distract from the response to what was expected to be a deadly and destructive storm.
Tropical Cyclone Alfred, as the low-pressure system had been named, did make its mark. It left 80,000 homes without electricity, caused $820 million in damage and killed one person. But the storm stalled and weakened as it approached the coast on 6 and 7 March, with slower winds than forecast and less structural damage as a result.
“We dodged a bullet this time,” Associate Professor Geoffrey Boughton AM told create. “It was a near miss, and whenever engineers have near misses, they should learn from them and work out what to do if next time it’s a direct hit.”
Devastating debris
Boughton is Senior Research Engineer with James Cook University’s Cyclone Testing Station, and co-author of a report into the damage to buildings caused by Tropical Cyclone Alfred.
When he says Australia dodged a bullet in March, he’s not exaggerating.
“I really was quite concerned when Cyclone Alfred was bearing down on South-East Queensland, knowing the extent of the damage that would be happening, because the wind speeds that were forecast were very similar to the wind speeds in Cyclone Seroja in 2021,” he said.
“It’s unlikely we would have escaped without deaths with that level of damage.”
A crucial mitigating factor this time, according to Boughton, was Alfred’s reduced wind speed – gusts up to 100 km per hour rather than the forecast 155 km per hour.
“If the winds were 20 km per hour higher, then they would have started to lift more roof tiles, pick up trampolines, garden sheds and rubbish bins, and caused fallen branches to fly further,” his report said.
“The low wind pressures and the lack of wind-borne debris contributed significantly to the low levels of structural damage in the area.”
Even though the buildings in the area had been designed to withstand wind speeds as high as the ones forecast, they had not been built to withstand the dangerous amount of debris that would result from such a storm.
“What is going to upset structures is not the wind speed, but the debris that wind is going to bring along with it – broken branches, rubbish bins, trampolines, broken bits of other buildings – and it’s the debris that is going to cause the problem,” he explained.
Wet and wild
Water ingress can also have greater ramifications than first apparent. Boughton’s report notes that wind-driven rain and basement inundation had such subsequent effects as damaging switchboards, short-circuiting fire alarms and cutting out emergency power.
“What often happens in a tropical cyclone is that there’s a reasonable amount of structural damage, and even a little bit of structural damage is going to let a lot of water in,” he said.
“It looks like in the worst affected areas that it’s going to be something like 2.5 per cent of buildings had enough water coming in to cause damage to the building.”
But he also describes water ingress as “low-hanging fruit” when it comes to improving the resilience of structures in at-risk areas.
“Often it’s a simple matter of detailing – getting the detailing right to keep water out, even when it’s windblown,” Boughton said. “The rain always hits the windward side of the building … and that’s the only side of the building that’s got positive pressure on it. So there’s a big pressure differential across the building envelope from the outside to the inside on the face that the rain is hitting.”
Getting warmer
Many of the issues Boughton identifies and the recommendations he makes are well understood in the most cyclone-prone parts of the country. The danger for the future, however, is that climate change exposes more and more areas to risk.
“Climate change could affect each and every one of us, and it means that we’ve got to be really smart about engineering our world to have the right level of resilience,” Boughton said. “I don’t think any of us know what the weather is going to be like for the rest of our lifetimes, but we do know that extreme events are going to get more extreme.”
That’s why an area such as South-East Queensland, which had been rated at a lower level of wind risk – or other parts of the country rated as lower-risk, such as Perth or Sydney – might need to begin building structures to higher standards than before.
And because the areas newly exposed to potential storms are more populated than the northern climes that are used to dealing with cyclones, the overall risk to the country is greater. The density of the population in those areas also makes addressing the problem more challenging.
“If you’re going in and changing how buildings are built, or retrofitting existing structures, that’s a much bigger task,” Boughton said.
“But we build buildings one at a time, so if we were to change the way we build in that area, it would happen gradually. New builds would have the features that are going to enable them to resist those kinds of events, and as the years go by, the proportion of buildings in that area that have been equipped to do the job are going to increase.”
“As a building is refitted or major work is done on a building, then that’s the time to bring it up to scratch. Over a period of time, a community can build its resilience to those kinds of events in the future.”
Boughton features in this EA OnDemand webinar on the topic of resilience in infrastructure.
