Research shows cars can be carried away by even shallow water

Researchers at the University of New South Wales have demonstrated that cars can be swept away easier than people in flooded water.

Researchers at the University of New South Wales have demonstrated that cars can be swept away easier than people in flooded water.

A team from the university's Water Research Laboratory dropped cars into a large tank at Manly Vale in Sydney's north on Friday to show how much force it would take for them to be washed from the road.

Principal engineer Grantley Smith, who led the research, said he was surprised at "just how little water it took to make even a large vehicle unstable".

"They became vulnerable to moving floodwaters once the depth reached the floor of the vehicle. Even in low water depths and slow flow speeds, floodwaters had a powerful enough force to make them float away."

In world-first tests using actual cars instead of miniature models, the researchers found a small car like a Toyota Yaris – which weighs 1.05 tonnes – was moved by water just 15 centimetres deep that had a flow speed of 3.6 kmh. It was carried away in 60 centimetres of water.

A larger Nissan Patrol four-wheel drive, at 2.5 tonnes, was moved by 45 centimetres of water and began floating in 95 centimetres of water, able to be pushed along by just a finger.

The cars were moved so easily partly because even shallow water can be deceptively strong, and partly because modern cars are so air-tight that instead of taking on water they get pushed along by it.

"People don't realise that even slow-moving water packs a powerful punch.

"Water is heavy: each cubic metre weighs about 1000 kilograms."

Greg Newton, the Acting Commissioner for NSW's State Emergency Service (SES), who helped to fund the experiment, said more than 80 cars were rescued in June when they became stranded in water during a storm that hit eastern areas of Australia.

"People need to re-think their actions and not drive into floodwater, because by doing this they are not only placing their lives at risk, but the lives of our volunteers who have to go out and rescue them," he said.

"Entering floodwater is the number one cause of death and injury in flood, so everyone should stay out and stay alive."