Lani Moore and Suzie Northfield, of Lismore, take a look at the flood water crossing Wyrallah Road in Lismore.
Lani Moore and Suzie Northfield, of Lismore, take a look at the flood water crossing Wyrallah Road in Lismore. Marc Stapelberg

Half metre deep flood flowing, like being hit by another car

AS OMINOUS storm clouds loom over the Northern Rivers threatening downpours, the SES are amplifying one clear message: if it's flooded, forget it.

Some carriageways remain closed while sections of other roads remain underwater and they're not predicted to subside any time soon with localised falls up to 40mm expected this evening and tomorrow.

Principal engineer at the University of NSW, Grantley Smith's research reveals the dangers behind what is the biggest killer during floods.

Many, Mr Smith said, underestimate the power of water, noting one cubic metre weighs a tonne.

Mr Smith headed experiments at the university's Water Research Laboratory mid last year which found that vehicles became vulnerable to moving floodwaters once the depth reached the floor of the car.

Researchers discovered small cars such as a Toyota Yaris can be moved by water only 15 cm deep and with a flow speed of one metre per second.

"The forces get very big, very fast," Mr Smith said.

He said even driving through flood waters half a metre deep flowing at a metre per second, slower than walking pace, pack a punch.

"If you can imagine two cars that weigh a tonne, it's like being hit by another car," he said.

Mr Smith said floodwaters 2m deep hitting a 20m-wide house at a speed of a metre per second is " a similar force to being hit by a 40 tonne semi every 15 seconds."

Talking from first hand experience, Casino woman Sonya Marks said what lies beneath unclear flood waters is just as dangerous as the water itself.

Ms Marks very publicly shared her first and last experience of driving through a swollen causeway near Ellangowan in 2006 for a nationwide SES campaign in January.

"For me, it was about 10 years ago but it's as relevant today," Ms Marks said.

"That's the first, last and only time I'd ever done anything like that."

 

A ute sinks in flood waters over the weekend near Grafton.
A ute sinks in flood waters over the weekend near Grafton. Jarrard Potter

Ms Marks reluctantly made the decision to cross the flood water with her kids in tow - two jumped out of the car to guide it through the water.

Halfway through the water, Ms Marks recounted the terror she felt as the road broke up under her 4WD.

"There's just too many things that can go wrong and it's just not worth it," she said.

"(The road) was the only thing I hadn't considered and it made a huge difference."

Ms Marks said sharing her story was worth being "hammered" by a handful of online trolls to campaign against the hazard of driving in flood waters.

"If one person stood up and said: "I saw that video and it made me re-think (driving through flood waters) and I turned around" ... then that makes it really worth it."



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