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So reading about the the Chicago Sanitary and Shipping Canal, you can see on the map that the route travels about 15 miles parallel to the Des Plaines River.

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I've been trying to find out why. This was built in the old days, very hard and expensive labor even with primitive steam shovels, and very expensive. But I cannot figure out why they went this extra 15 miles when they could have just cut the path straight into the Des Plaines.

I did find the older Illinois and Michigan Canal and for some reason this one too took a southern turn instead of continuing west into the Des Plaines, which would be a much shorter route.

Was there something wrong with the Upper Des Plaines that made it unavigable to shipping? Was there some expensive land or buildings that they didn't want to encroach upon? Every cause that I can think of, when searched specifically, gave me no good results. So I'm now more curious than ever. There must be a reason for this longer route in both canals.

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    I suspect it's about keeping the watersheds separate, rather than about navigation.
    – Pieter Geerkens
    Commented Nov 4, 2022 at 15:43
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    Well, the ~70 foot elevation difference between the Des Plaines near current O'Hare airport and the lake (the river is higher) is one clear indicator. Canals go out of their way to have very gentle water level changes.
    – Jon Custer
    Commented Nov 4, 2022 at 15:49
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    @PieterGeerkens The Lock at the entrance to Lake Michigan will regulate the flow between watersheds. Once you connect with waterways, there is no way to keep the watersheds separate anymore. The best you can do is regulate it with locks.
    – DrZ214
    Commented Nov 4, 2022 at 15:59
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    @JonCuster I just checked on google earth, Lake Michigan at 175 m and the Des Plaines (at the part where the CSSC turns SW) is at 177 m. But then why not just use another lock? They already built one at the Chicago mouth and also at the junction where the CSSC and Des Plaines actually converge.
    – DrZ214
    Commented Nov 4, 2022 at 16:23

1 Answer 1

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The answer is there in the name:

Chicago Sanitary and Ship Canal

Notice "Sanitary" comes first -- the primary purpose of the canal was sanitation, and shipping was only secondary. As Chicago grew, its eponymous river turned into a big sewer. The Chicago River flowed into Lake Michigan, from which the city drew its drinking water.

In order to keep the city's poo and industrial waste out of the lake, they had to send it somewhere else. Fortuitously, the precursor to Lake Michigan had drained south during the last Ice Age, and in that channel, the nearby Des Plaines river drained south to the Illinois river and eventually the Mississippi.

The idea behind the project was to make the Chicago River run backwards, and drain into the Mississippi watershed instead of Lake Michigan.

However, as you said in the comments, the Des Plaines River was 2 meters higher than the canal at Portage Creek, where the canal approached it. A lock would have permitted shipping, but would have prevented the city's wastewater from draining south and becoming somebody else's problem.

So, the canal was dug parallel to the river until the river's elevation had lowered enough to join it. It would have meant more digging to follow the river's course.

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  • This makes sense, however is there any source talking about this? I'm trying to find some book that talks about the surveyed route and why. I already tried free sites like wikipedia and youtube and as usual came up empty. And also, why would it mean more digging to connect directly to the Des Plaines? Do you mean a drastic deepening of the Des Plaines?
    – DrZ214
    Commented Nov 4, 2022 at 18:07
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    @DrZ214 The World Book Encyclopedia used to have this kids' supplement called "Childcraft" where I read it for the first time when I was about 7.
    – Spencer
    Commented Nov 4, 2022 at 19:51
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    @DrZ214: Also worth noting is that if you're working mostly with hand tools, as they would've been in those days, it's a lot easier to dig a channel when it's dry than when there's a river flowing through it. So, in order to deepen the Des Plaines River, they probably would've first had to dig a channel alongside it anyway, and then divert the river into the new channel, just so they could dig in the original riverbed.
    – Ilmari Karonen
    Commented Nov 5, 2022 at 11:14
  • So Lake Michigan is slowly being drained into the Gulf of Mexico?
    – Dan
    Commented Nov 6, 2022 at 16:32
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    @DanSheppard Only by as much as the Corps of Engineers allows. There is also this "rain" stuff that tends to replenish the lake.
    – Spencer
    Commented Nov 6, 2022 at 17:18

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