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Up a Lazy River

Meandering through a classic theory of why rivers meander

Brian Hayes

Water runs downhill—we all know that. As a rule, it follows the path of steepest descent, seeking out the shortest and fastest route from top to bottom. So how can we make sense of meandering rivers, which wiggle-waggle down the valley, prolonging their journey to the sea and greatly lengthening their course? Why doesn't the flowing water—acting under the tug of gravity—just carve out a shortcut across all those loops?

The Irtysh RiverClick to Enlarge Image

I first encountered the mysteries of meanders in an article by Luna B. Leopold and Walter Langbein, published 40 years ago in Scientific American. They gave a lucid account of how meanders form and why they assume their characteristic sinuous shapes. I was a student at the time, and the article made a lasting impression. Not that I was inspired to go off and pursue a career in potamology, but the Leopold-Langbein theory of meanders was an eye-opener all the same. It brought home to me the curious fact that the world is a comprehensible place: You can look at a landform, say, and expect to understand what you see. The patterns of nature make sense, if you know how to read them.

Luna Leopold died last February at age 90. Reading accounts of his life and work led me back to that fondly remembered Scientific American article from 1966, as well as another article published a few years earlier in American Scientist. I found them still lucid and engaging—and yet, on reflection, not quite fully satisfying. It's not so much that the answers now seemed less compelling, but they led to many further questions, which I had lacked the wit to ask the first time around. Maybe nature is indeed comprehensible, but I couldn't say that I truly understood river meanders. So I delved deeper into the work of Leopold and his colleagues, and I looked at how others have approached the same problems. I even tried a few simplistic computer experiments of my own. After all that, there's still no shortage of questions.

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