Why do Rivers Curve?

Wednesday, 30 March 2016

Looking at curvy rivers on topographic maps or Google Earth has always been really interesting to me and for the longest time I’ve wondered how that snake like shape came to be. You would think that since a straight line is technically the shortest and easiest route to the ocean that nature would like straight lines. Nope.

After stumbling upon the video below about why rivers curve, I discovered that all it takes is a little bit of disturbance and a lot of time. Take for example a tree falls over and into the water. The current is diverted slightly allowing the riverbank to slowly erode on the opposite side. The slight change in current direction then bounces off that bank and gets diverted back over to the other side causing more erosion and eventually a curve in the river. Of course this doesn’t happen overnight and that is where time is the key factor.

A diagram of a river starting to curve due to erosion.

Check out this time lapse of a river Peru to how much the river chances even over that short number of years.

River erosion timelapse.

Here is a final fun-fact for your next boring office party. It doesn’t matter how wide or big the river is, if it is flowing over soft ground, the length of an s-bend curve will be roughly six times the width of a river. So that means while a narrow river will look wigglier when comparing to a large wide river the ratio of length/width of the wiggles will always be the same no matter which river it is. Hydrodynamics are amazing.

River curve ratio. The length of an s-curve is six times it's width.

David Johnston

David Johnston

David Johnston has been introducing people to the sport of sea kayaking for the past 15 years. He is a senior instructor trainer with Paddle Canada and teaches for several paddling schools in Ontario, Canada. Full Bio.

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