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Rudi Kiefer: Lake levels fluctuate more in South
Rudi Kiefer
Visitors to North Georgia from Minnesota or Wisconsin are sometimes surprised by Lake Lanier. Frequent changes in water level aren’t the norm in their own home states. The difference is that in Georgia, all lakes are artificial.

Some 25,000 years ago, during the latest of four known “ice ages,” giant glaciers covered half of North America. The ice never made it any farther south than Ohio and Indiana. The massive Laurentide ice sheet, up to 10,000 feet thick, put enormous pressure on the bedrock underneath.

Like a hydraulic press/bulldozer combination, the glacier carved out basins that would fill with water as the ice was melting away. Not only did America’s Great Lakes form through this process, it also produced thousands of smaller lakes in the states and provinces around them.

On a map, lakes formed by glaciers show rounded outlines, gouged out by glacial ice. Lakes in Georgia have a jagged, star-like shape. That’s because they are engineered from rivers. The pointy edges are the tributary streams merging with the main stream. It doesn’t make them any less useful and beautiful. But their levels are more prone to fluctuation than the glacial lakes of the North.

To have a lake like Hartwell, Chatuge, Lanier, Allatoona and so many others, you first need a valley. Most valleys have a stream draining them. You then need to find the narrowest point of the valley, where a dam can be built most efficiently. The dam, intended to block the river and accumulate water on the upstream side, can be made of stones and dirt, or as a solid concrete wall.

There must be a separate emergency overflow channel, in case the lake level gets too high. Usually, the outflow from the original river is run through a pipe and turbine, where it produces electricity before emerging below the dam. The amount of water allowed to leave the lake is constantly regulated by the Army Corps of Engineers. Depending on season, rainfall, even time of day, the lake and the river downstream are adjusted all the time.

Many of the lakes in the U.S. South were built for flood control, like Fontana Lake near Bryson City, North Carolina. But in their use as water reservoirs, wildlife and recreational areas, and for control of groundwater levels they are completely equivalent to their natural cousins farther north.

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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