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Earth Sense: Be aware of your flood risk

POSTED: May 11, 2014 12:14 a.m.

Scenes that we’ve only seen in major hurricanes played out early in Florida and Alabama on April 29-30. The Florida panhandle received 2 feet of rain, causing floods in Pensacola and surroundings. The dramatic footage from the Gulf Coast, and the death of a driver whose car got submerged, speak for themselves.

But it raises the question: What types of places get flooded? Physical geographers distinguish between two types: area floods and flash floods.

The first happens where the terrain is flat, and a severe storm brings heavy rain. That’s what happened on the coast, where elevations are minimal, and drainage is slow. When area floods build rapidly, residents are sometimes desperate to escape in their vehicles, but “every which way we turned, there was a big pile of water,” a news report quoted one mother, trying to drive away with her 2-year old son.

Area floods are unlikely in North Georgia due to our hilly terrain. It drains more quickly than the coastal plain, but therein lies the risk of flash flooding. Had the April 29 storm produced similar rain totals here as it did in Florida, we would have seen torrents of water draining the stream valleys, and possible landslides from the mountain slopes. It happened at Peeks Creek near Franklin, N.C., in 2004, taking five lives.

Flood waters run downhill, so you can evaluate your flood risk. Are there two slopes coming together at your property? If so, their funneling effect can steer a torrent of water onto the house. Is the house built on flat ground, with one or (worse) two hillslopes near the property? This may constitute a floodplain, which is why the ground is level from stream sediment to begin with.

Is the house located on a hilltop? In that case, drainage is away from the property and flood risk is minimal. Are you located next to very large, paved-over areas like parking lots and big commercial buildings? Heavy rain could overpower storm sewers and send flood waters to your property. Does the driveway slope down into the garage? Expect water to enter underneath the garage door.

One crucial point to observe in all flood types: Never drive onto a flooded roadway. Cars begin to float in just 10 inches of water, making the driver lose all control. Waiting for rescue, on a rooftop if necessary, is the lesser evil.

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.


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