In Darwin’s Ghost, Steve Jones states:
“Measurements of dozens of real rivers and computer simulations of many more show that the relationship between the shortest possible path across a plain and their actual length is always the same. It is pi. Each river, whatever its size, goes a little more than three times farther than it needs on its way to the sea.”
How is this possible? I’m completely floored! Is it true?
Maybe the average ratio is pi. But it’s impossible for it to always be pi.
Is the ratio really pi? Right out to the zillionith decimal place? Or is the ratio just about 3.1 or so?
100% bullshit.
The study of river forms and their interaction with underlying geology is called fluvial geomorphology. While the science is quite complicated, Some of the factors used in classifying a river are slope, underlying geology, and sinuosity.
Sinuosity is basically what Mr. Jones is referring to: a measure of actual stream mile distance vs. distance “as the crow flies”. I assure you that his claim that all streams have a sinuosity of 3.14 is entirely false. Sinuosities of streams may approach unity (1:1), in the case of steep, mountain streams, or may be greater than pi in the case of some coastal plain streams.
People want to see magic numbers and symbolism often where there is not. Perhaps this was a literary device that used a bad, made up example, rather than one that can actually be demonstrated like the golden section 1:1.1618… , which is found often in nature, particularly in spiral forms such as nautilus shells and glaxies.
I would think that for a river in a flood plain pi would be somewhere near the upper limits of sinuosity - once a given loop of a river nears pi shouldn’t a new channel form and the old one become an oxbow lake?
My guess is that someone did a simulation showing that, what with channel formation, a stream straight across a level flood plain deforms in such a way that its sinuosity converges relatively steadily to pi.