The River That Flows Both Ways or “Things I Learnt While on a Train Passing Through the Monotonous Midwest Countryside Part 1”

Photo: Wikimedia commons

Photo: Daniel Schwen (CC BY-SA 4.0)

Corn, Soybeans, Barns, Corn, Barns, Soybeans, Small Town, Corn…. The view today from the California Zephyr, rattling across the Interior Plains of the US, is a little monotonous. It makes the dull Canterbury Plains look like a World Heritage Site. A perfect time to research a little about the area, and my next stop – Chicago Illinois – on my smartphone.

The Midwest has been geologically stable for the last nearly 2 billion years: it is the centre of a continental plate, covered with debris from mountain ranges to the East and West. Thus, it is flat. So flat that sanitation-minded Engineers could reverse the flow of the Chicago river in 1900, by digging through the two-storey high ridge that separates the Great Lakes watershed from that of the Mississippi. People made Lake Michigan flow into the Mississippi more than a century ago!


Reversing the flow of the Chicago, 1899. Public Domain

This meant sewage stopped flowing into Lake Michigan – a source of drinking water for the burgeoning city. Apparently no-one cared that Chicago’s sewage now flowed into the Mississippi watershed (because that was already pretty polluted?). It also opened shipping from the Great Lakes down to the Gulf of Mexico via the Des Plaines and Mississippi.

The Chicago River has a mind of its own though – in winters, when boat traffic on the river is low, water underneath the surface starts to flow back into Lake Michigan, while the surface water continues to flow away from it. This is, apparently because of some weird fluid dynamic effect I’ll never understand called a “gravity current”, or “density current”.  That must be one pretty flat river to be able to flow both ways at once.

Chicago River at Night

Public Domain

(edited twice for clarity and zest)