This is an excerpt of an interview soon to be included in a little zine I’m helping with. If all I got to do in life was pick the brains of scientists, it would be enough. –Jake
A RIVER IS THE AUTHOR OF ITS OWN GEOMETRY
Rivers are ephemeral. Their unique shapes are works in progress, lines continually redrawn by factors large and small. What’s the source of their peculiar behavior and beauty? We sat down with John, a graduate research assistant at the University of Minnesota’s Department of Civil, Environmental and Geo-Engineering, to talk about water, people and the dynamics (physical and historical) that bind them together.
What got you hooked on rivers?
As a kid growing up on a farm in Tennessee, streams are all over the place. Romping in rivers has always been part of my life. My “watershed” moment came hiking the Appalachian Trail. On those river crossings, you step through what seem like little creeks, but go up to your waist. You can feel the force, even if it doesn’t look that deep. When you’re IN it, when you feel it, you realize how powerful even small rivers can be. That trip connected me to rivers and flowing water.
What’s your focus these days?
My dissertation is on meandering river dynamics, how rivers move about their flood plains and rework the surface of the earth. You see the effects of winding rivers in very diverse environments: on the Mississippi, on glaciers, on Mars, Saturn’s moon Titan, even underwater when fresh water flows into saltwater before they mix.
So why do rivers wind like that?
All kinds of factors cause rivers to move: landscape, soil, rock, precipitation, human impact. Once you change anything in a system, nature adapts. An interesting study was done in Yellowstone National Park, where the streams were considered wildly meandering. After wolves were reintroduced to the park, the meandering stopped. Turns out that when the animals hunted by wolves were chased off, the vegetation they were eating grew again and strengthened the banks.
Up until the 1980s, people explained the meandering pattern by invoking the river as a conscious entity—“the water wants to move”—without a physical basis. Now there are many good theories. I think the best one is that turbulence in the fluid causes the patterns. But we’re still looking for a unified theory of river meandering.
Tell us about your river.
I study the Ucayali River in Peru. It has very high sinuosity, which is a measure of how winding it is (higher number = more winding). This river has moved 100m per year laterally. That’s comparable to the rate of movement on the Mississippi River pre-settlement. But the watershed of the Mississippi is 10,000-times larger than the Ucayali. This wild migration is a result of lots of eroded sediment from the Andes Mountains to the west and rains from the Amazon to the east.
How are people part of the dynamic?
Rivers are very active. Every time you build a bridge or a dam, you cut off some of the hydrodynamic processes that would affect the channel. When we somehow lock the system into place, we drastically reduce the changes. How does human impact affect meandering dynamics? When we do an activity, how far does it propagate? I want to better understand the dynamics. It’s what the stream restoration industry is all about.
Can we build a better stream?
In the industry now, if you put in a stream and it moves, they say your design has failed. But we need to remember if we want a stream in anything like a natural state, it needs a framework so it can move. We need to learn to design for migration.
Ecologically, it’s very important. Water in a stream will seep into the ground water and then pop up later, and winding its own way encourages that process. They say, “a river is the author of its own geometry”—its own engineer, in a sense. And meandering is the mechanism.