Rudi Kiefer: Flash flooding poses a deadly danger, don’t ignore warnings

Harvey will make it into the history books as one of the great disasters of the 21st century — “great” because of the unprecedented losses caused by the storm. For the Hall County area, there are things we can learn from it.

It’s been emphasized by the National Weather Service time and time again, but gets ignored just as often: Don’t drive into a flooded street. News images and videos show plenty of fresh footage of people trying to plow through the waters in their cars and trucks.

Having four-wheel drive doesn’t make a vehicle more apt at river crossing. The problem isn’t the loss of traction; it’s the gain in buoyancy. Just a foot of water on the road will make the average car start to float. It takes more for a tall truck. But it, too, will float as soon as its critical depth is reached. 

Floodwaters on the road don’t tend to sit still. They can have a very strong current, and that’s what will grab the vehicle, lift it off the road surface and drift it away. At that point, the driver will have zero control. 

Flood currents usually find a deeper basin somewhere to pour into. That’s where it gets really dangerous because as soon as the car gets dropped into deep water, it can roll and overturn with its occupants trapped inside.

Even if the flood is only shallow, the engine is still going to stall. The car then fills up with water and, if lucky, its driver gets to sit on the roof waiting for emergency rescue.

Area flooding of the Houston type isn’t going to happen in Gainesville. We aren’t located in a flat coastal plain. When the remnants of Hurricane Katrina passed through Hall County, it didn’t cause widespread inundation. What we got instead was flash flooding. It has a smaller footprint but is more deadly than area flooding. 

A flash flood is the sudden surge of waters in a stream, combined with the runoff from slopes and storm sewers. The more area is paved over by streets, parking lots and businesses, the quicker and more powerful the flash flood. When the Weather Service issues a flash flood watch, avoid walking, driving and parking in low-lying areas near rivers and streams. If water is covering the roadway ahead, find an alternative route.


Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at gainesvilletimes.com.

Regional events