Question: I live in Alaska and there’s a lot of meandering rivers in this state. In fact, I’ve flown over this one not far from my home in Prudhoe Bay. Flying over them lets you see just how sinuous these rivers are. What I’m curious about is why do some rivers meander and others flow straight? — DW, Prudhoe Bay, AK
Answer: It all comes down to topography, DW. If a river is confined by a channel with steep rock walls, as is most of the Colorado River, then no — you won’t get much meandering. But if the river runs through a relatively flat landscape, meandering will almost certainly happen.
Even if you start with a perfectly straight stream, if the meander belt is wider than the stream, the stream course will be unstable. Random variations in stream flow and turbulence can initiate the processes of erosion and deposition. Once initiated they tend to be self-reinforcing through positive feedback loops.
Since a stream always flows faster on the outside of a curve, erosion will be enhanced there and lead to even greater curvature. On the inside of a curve flow is slower leading to enhanced deposition of silt, forming what is called a point bar. Here’s a graphic that shows the evolution of an originally straight flow into meandering, and eventual cutoff of the meander to form what is known as an oxbow lake (common around meandering rivers):
Oxbow lakes eventually fill with sediment and become valuable wetlands for wildlife. Though some have persisted for centuries, most will dry up at some point. A meander cutoff is usually caused by flooding, when water seeks to take the shortest path. But cutoffs are sometimes intentionally dredged to straighten (and shorten) a river used for cargo transport. This was done on the Mississippi River by the Army Corp of Engineers starting in the late 1800s. Here’s a detailed looked at how that works:
Oxbow lake formation in a meandering stream, Phil Reiker, NPS Geologic Resources Division
Due to the slope of the channel, erosion is more effective on the downstream side of a meander. Therefore, in addition to growing laterally, the bends also gradually migrate down the valley. Check out this amazing article by the National Park Service (NPS) showing historic course changes in the Mississippi:
https://www.nps.gov/vick/learn/nature/river-course-changes.htm
Restricting the meandering of a navigable river with levees and man-made oxbow lakes is not an easy or fast job, but it’s been done to many rivers in the US and other countries. The advantages of “river straightening” are obvious. But there are some negative impacts.
Coincidentally, as I was writing this post, I took a TV break and stumbled across an old Perry Mason episode — The Case of the Roving River (1961). The issue at hand was property lines along a meandering river. Turns out the law says property lines will follow a (gradual) change in the river’s course, so your length of riverfront doesn’t change. But if there’s a “rapid” change due to flooding, a property owner could lose access to the river. Interestingly, if the property spans a seismic fault zone, the originally surveyed boundaries remain at their original latitude/longitude coordinates. This means that the property owner will be continuously acquiring new physical land over time on the opposite side of the fault.
So river meandering is a naturally occurring phenomenon, DW, given the right terrain. If you ever fly over that river again take a photo and we can see how things have changed. There’s two prominent meanders in the photo you linked to, and the remains of several oxbow lakes, but the image is dated 1973.
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