Weather Notebook
Bryan Yeaton

Cars and High Water
Mon Jun 27, 2005

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Flooding, particularly flash floods, kills more Americans annually than tornadoes, hurricanes, or lightning. The majority of deaths—about sixty percent—occur when victims are trapped in a vehicle swept away by rushing floodwaters. Hi, I’m Bryan Yeaton for The Weather Notebook.

We greatly underestimate the power of moving water. Moving at 4 mph—walking speed—water exerts a force of 66 pounds/square foot against any object. A liquid depth of only six inches can sweep you off your feet. A typical flood moves at 12 mph, or nine times walking-speed force, and flash floods may exceed 60 mph in narrow gaps.

Another factor helping to push your car off the road is buoyancy; cars will float. We consider cars heavy objects, but for each foot rise in water level, their downward weight on the road decreases by around 1500 pounds. At a depth of only two feet, about up to door level, moving water can easily sweep away a car or light truck. Six o’clock newscasts around the country show dramatic footage of many such events.

Here are some safety tips:

1.) During flooding, avoid places where water can suddenly rise or accumulate, such as river bridges, highway dips and low areas.

2.) Never attempt to drive over a flooded road. Water depth is not always obvious, and the underlying roadbed may be completely washed away. If your vehicle stalls, you can become trapped. Many deaths occur when rapidly rising water engulfs occupants in their vehicles and sweeps them away. As the National Weather Service says: "Turn Around—Don’t Drown!"

3.) If your vehicle does become surrounded by water or the engine stalls: if you can safely get out, abandon your vehicle immediately then climb to higher ground.

Thanks to our contributing writer, meteorologist Keith Heidorn. The Weather Notebook is funded by Subaru of America. Find us online at

Today's Links

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