Over the next couple weeks, I’ll post on happenings in my research group over the last year. I’ll kick things off with a problem I’ve been wrestling with: what defines a meander bend in a river? This is a peculiar question to ask, particularly for someone who dedicated a doctoral dissertation to meandering rivers. But these days, familiar things are starting to look strange to me. One of those strange and beautiful things is a meander bend.
Across Earth’s surface, rivers great and small form meander bends. Some of them are symmetric like bell curves, while others are asymmetric like bananas. A fascinating quality of meander bends is that their basic proportions are consistent: the wavelength of a meander bend is about 10 times the width of the river channel, give or take. Luna Leopold and Reds Wolman made this discovery in the 1950s, establishing one of the foundations of quantitative river studies.
Another interesting observation: the same meandering pattern occurs not only in rivers, but also in other natural, channelized flows: think of a pure-blue stream flowing on top of glacier, or lava that once flowed through a lava tube.
Considering these examples, meander bends seem to be a basic characteristic of natural flows in channels. But many rivers have also been drastically reshaped by humans through damming, straightening, and other adventures in engineering. A substantial industry has developed to restoring rivers, which often requires developing a nature-based design.
So from trying to understand one of the most common landforms, to designing plans for river restoration, there is a need to identify patterns in the shapes of meander bends. Over the years, this need has motivated several interpretive approaches for mapping and classifying meander bends. But it’s been hard to pin down a set of objective rules that one could use to define what a meander bend is. Another pitfall is the human bias to seeing patterns where none exist — a phenomenon Prof. Tom Coulthard at the University of Hull (UK) colorfully termed “fluvial apophenia.”
So what exactly is a meander bend? And how might one test for patterns in their meander bend shapes, without assuming that such patterns exist? I’ll describe a new solution to these problems in the next post.