Year: 2017
Every year floods cause enormous damage and loss of life on a global scale. A detailed analysis of flood fatalities in Australia by Haynes et al. (2016) noted that 1,859 people have died in floods since 1900, more than any other type of natural disaster, including bushfire.
The study noted that while flood fatality rates are generally falling per capita, the number of fatalities that occurred in vehicles, particularly four wheel drive (4WD) vehicles has increased in the last fifteen years.
It is clear from this brief overview that there is a need for an understanding of the mechanisms by which vehicles become unstable in floodwaters.
In a world first, the flow vulnerability thresholds for two vehicles were tested at full scale in a specially configured tow tank at the UNSW Water Research Laboratory.
The test program and analysis presents a novel approach to the derivation of stability curves for vehicles in flood flows, by dissecting the forces that impact the vehicle, applying appropriate factors of safety for real-life flood conditions (as opposed to controlled laboratory conditions), and evaluating vehicle stability directly from the stability balance equation.
Observations from the testing confirm that where floodwaters impact the body of the vehicle, the vehicle is at greater risk of losing traction and being washed downstream. Flows that do not impact the body of the vehicle (hitting the wheels only) are generally considered safer for that vehicle.
The research testing and analysis described in our report aims to improve the knowledge and information available describing the vulnerability of vehicles as they enter floodwaters and quantify the flow conditions that might cause vehicles to become vulnerable to being washed away.
WRL technical report
Smith, G P, Modra, B D, Tucker, T A and Cox, R J (2017) "Vehicle stability testing for flood flows" WRL Technical Report 2017/07 May
Vehicle stability failure mechanisms in flood water
Illustration by Anna Blacka, UNSW Water Research Laboratory
Cars in floods - Stability and toppling at a causeway
Illustration by Anna Blacka, UNSW Water Research Laboratory