The Chicago River is flowing backwards, rather than going downhill from inland Illinois into
Lake Michigan instead it goes that way, in the opposite direction.
This isn’t some quirk of nature, but an engineering megaproject - indeed four engineering
megaprojects - on a scale quite unlike anything else on Earth.
So, what does it take to reverse a river?
To find out why you might want to do that we need to go back to 1850s Chicago.
Over the preceding two decades the city had grown from a tiny outpost of 100 souls into
a thriving industrial center of 100 thousand.
Nestled between the banks of Lake Michigan and the Chicago River it formed the central
node of a sprawling North American trade network.
Unfortunately, it was also a very flat, effectively lake-level swamp where stagnant pools of human
waste formed the perfect breeding ground for pathogens.
In 1845 an outbreak of Cholera had killed 6% of the city’s population.
In 1855 the Chicago Board of Sewerage Commissioners brought in Boston engineer Ellis S. Chesbrough
to construct what would become America’s first sewage system.
The idea was to lay some pipe, feed it into the river, and have the river take all of
our human waste out into the lake.
In order for pipe to work it needs to be installed at a bit of an angle so that gravity can bring
all of that sewage downhill.
However, since the streets were already effectively at river level, this meant that the new pipe
would need to be laid up to four meters above the existing street.
That was ok, we did that, put in some soil, and called it a day; effectively redefining
street level for the entire city.
Apparently the city’s buildings didn’t quite get the memo and soon found now their
ground floors several meters beneath the new street.
This didn’t just make egress really inconvenient, but also provided a new home for the stagnant
pools which we were trying to get rid of in the first place.
In 1858, engineers James Brown and James Hollingsdale, rose to the challenge.
Employing a team of 50 workers and using 200 jackscrews they were able to lift a 700 tonne
building some 2 meters back to the level of the new street level.
The pair raised another 50 buildings that year and soon engineers from all over the
country were in Chicago competing to see who could lift the most spectacular structures.
While some used hydraulics brought in from California, most instead preferred to use
manual labor and an insane amount of jackscrews.
These combined the mechanical advantages of a twisting inclined plane with the extra torque
you get from using a super long rod.
Incredibly Chicago’s bustling city center was able to continue on with business as usual,
with one guest at the Tremont House Hotel writing in bafflement that the steps onto
the street seemed to be becoming steeper and steeper with every passing day for no apparent reason.
I think this first Chicago megaproject would perhaps be better well known if it wasn’t
for the 1871 Great Chicago Fire which incinerated the city and erased everyone's hard work.
Another problem had also started to become evident.
As the city, its population, and its industries grew, so to did the level of pollution in
the Chicago river.
When it wasn't spontaneously catching fire you could walk across it on floating rafts
of sludge.
All that muck eventually made it’s way out into the lake.
The same place people were getting their apparently clean drinking water.
Cholera deaths and illness continued pretty-much unabated.
In 1863 Chesbrough then proposed a second Chicago megaproject; digging the world’s
biggest, longest, deepest, underwater tunnel with which to collect water from some three-kilometers
out in the lake and bring it into the city for people to drink.
Using the tunnel shield technique discussed in our Boston episode, during the day diggers
would remove the required material and at night brick layers added in the required supports.
Working from opposite ends it took them two years but eventually they met in the middle,
celebrated for a while, and then got right back to work.
This time digging a six kilometer long tunnel.
As it turns out, the initial water collection crib was still too close to the polluting
waters of the river and people were still getting sick.
Eventually nine of these intake cribs were constructed of which two are still in use today.
However, putting them further and further out was only ever going to be a temporary solution.
Something serious would need to be done.
Obviously a little bit upset, Chesbrough then proposed his third and most insane megaproject yet.
If the problem was with the river taking its pollution out into the lake, then why don’t
we take the river and its pollution somewhere else.
Ideally, into the Mississippi where it would then empty out into the Gulf of Mexico.
This would have an extra benefit of connecting the city to yet more trade routes.
Unfortunately there was a slight problem, the Subcontinental Divide was in the way.
Although construction delays brought about by a civil war meant that Chesbrough never
got to see his project underway, eventually the work of explosives, steam shovels, and
thousands of laborers took to the task of removing the required 33 million cubic meters
of soil and rock.
This provided an excellent training ground for the engineers who eventually went on to
build the Panama Canal; they had indeed constructed a 45 kilometer long canal right through the
divide - downwards sloping in order to allow the water to flow through.
When it was completed in 1900 the revered Chicago river contained a substance that actually resembled water.
That isn’t to say though that the project was entirely without it’s downside.
Where the waters empty out into the Gulf of Mexico they form state-sized algal blooms
which have been devastating to marine life.
Although a fourth Chicago megaproject - the construction of the world’s largest wastewater
treatment plant - has improved water quality somewhat, it still hasn’t been enough to
remove the bloom-inducing levels of phosphorus mineral.
Where the waters pass through farmland they have inundated the soil, which has really
damaged crop yields.
Although you might expect that all these downsides are limited to downstream, as it turns out
this new watercourse has provided an unexpected back door for invasive species such as carp.
For the moment these are kept at bay with a bubble curtain and an electrified fence
near the town of Joliet, but if they were to ever break through this could put the Great
Lakes’ seven-billion-dollar-a-year fishing industry in jeopardy.
Despite these drawbacks, Chigago’s four megaprojects are a triumph and wonder of engineering.
They turned a Cholera-infested swamp, into a river that occasionally caught fire, into
a backward-flowing waterbody, and finally into the semi-pristine waters at the heart
of one of America’s most important cities.
As for what’s next for Chicago I’ve got no idea but I’m sure it will be suitably mega.
This has been James Dingley from the Atomic Frontier.
Keep Looking Up.