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Earth Sense: Geology of an area can lead to flooding
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With the Louvre and the Musée d’Orsay threatened by flooding this month, Paris deserves prominent news headlines.

But my attention was riveted on the Hohenlohe region of southwestern Germany, my ancestral home. The cities of Kunzelsau and Schwabisch Hall, surrounded by pretty farming towns and villages, are no strangers to flooding.  

Locals recall Christmas 1993, when heavy rains put large areas under water. Right on the heels of that 100-year flood, another catastrophe followed in the first week of January 1994. Fast-forward 20 years, and again the aforementioned towns and villages found themselves inundated this month.

To understand why there are recurring floods, one needs to look at the geology of the province, which resembles the region around Bowling Green, Ky.

In Kunzelsau, flat layers of limestone alternate with sandstone, forming tall plateaus interrupted by narrow valleys.

While sandstone can absorb lots of water, limestone cannot. The top layer, clearly visible on the steep hill slopes, is limestone. Rainwater intrudes into countless cracks, natural conduits and caves.

With very little delay, it emerges again in springs from the bottom of the layer, where the sandstone is already saturated. From the air, it looks like the Kocher River caused all the trouble. But most of the water is coming from inside the rock strata, down the hills in torrents of mud and even rising below the riverbed.

In normal weather, drainage is adequate for keeping the river in its bed. But severe rainstorms quickly fill all the “internal plumbing” of the limestone layers, and the rock disgorges water like a bathtub with the plug pulled.

The other aspect is that the larger towns are located in the valleys, due to the steepness of the hill slopes. This puts most of their area into the floodplains of the streams. Smaller villages are present on the flat-topped ridges, and even a few castles from the early Middle Ages.

In ancient times, they were the equivalent of toll gates, controlling and taxing the transport of goods down in the valleys. As modern commerce evolved, merchants and transportation became concentrated in the valleys, and the hilltops were taken over by farms and a sprinkling of homes.

But the rivers are likely to continue claiming their floodplains. As long as the major institutions, businesses and residential districts in hard-hit Schwabisch Hall and Kunzelsau remain near river level, catastrophic floods will keep occurring.

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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