Travelling in a Sinking City
Updated: Feb 5
Water is both a blessing and a curse. It is of utmost importance for human survival, so why is it also problematic? While I am currently gunning for my P.Eng Certification in the next couple of years, I cannot sit here and say I have designed and built an entire city before. However, I did spend a very long 11 years in schooling, in addition to working in the field, consequently learning a thing or two. One of those things being that the study of hydrology and hydraulics is crucial for design.
My actual hydrology notes circa 2018
Engineering designs go way back, some brilliant, some terrible. Not terrible because of lack of intelligence but terrible because there was yet any history to base it off of. The Incas shaped their Yucay limestone blocks with perfection, the rock cuts seemingly as smooth as butter. The Romans managed to construct an aqueduct towering nearly 50m in height without the construction equipment we have today. The Egyptians assembled enormous pyramids...or was it extraterrestrials? Regardless, what do all three of these places have in common? They are still standing today.
How can these historic structures still be standing strong today but others have re-routed the future for failure? When you think of a sinking city, your mind may automatically veer towards the obvious...Venice, Italy. However, there is a different city in particular I wish to discuss, as it was a quick stop along my recent travels.
Mexico City or Ciudad de México is home to a few people...just over 22 million to be exact, making it the 5th largest city in the world. To give you some perspective, Mexico city spans an area of 1485km2, while Canada is nearly 10,000,000km2 with a population of 39 million people.
Travelling through Mexico City - December 2022
Let's flash back to the year of 1325 and ask ourselves, who in their right mind would plan and build a city expecting it to grow to over 22 million people in the year of 2023? Here I'll give you the answer...absolutely no one. So it didn't seem too crazy at the time to build a city on an artificial island in the middle of a lake. Nor did it seem to be a big deal later on when they started draining the lake to prevent further flooding of their ever growing city.
Tenochtitlán in the middle of Lake Texcoco
Lake Texcoco is the lake that once covered the region that is now known as Mexico City. Having a city close to such accessible water is convenience at best but when we fast forward to the 1500s, the Spanish conquered the City and depleted the Aztecs of this fresh water by streaming salt water in. Fast forward again to the 1600s, following a 5 year flood, the solution at the time to keep the city going was to completely drain Lake Texcoco.
This explains the clay foundation that Mexico City is built upon today and the lack of groundwater. Once a lake and now covered in concrete and asphalt, the City is depleting any water resources they have without sufficient time for them to replenish. How could they in a concrete jungle? This is exactly why permeable materials (AKA grass being one of the best) should not just be considered when designing but required.
Travelling in Mexico City - February 2014
What is the result of all of this? Well the thing is, Mexico City is sinking and has already done so by 30 feet (or just over 9 meters). I know I am pretty short but that's nearly 6 of me. How crazy is that? At the exponentially rate that Mexico City is sinking at, what you might find even more alarming is this drastic meterage does not even categorize this city in the top 36 cities to sink first. This is because the city is located at such a high sea level to begin with, resulting in 25% lower oxygen levels than those cities at sea level (but we can speak about this more when we discuss air pollution in the near future)!
So in my recent travels, did I notice the difference from my first time to Mexico City in 2014 versus the second time in 2022? I recall learning about this sinking situation in school but to be completely honest, I wasn't really looking too far into that in 2014. Now I wish I had paid more attention to the building foundations around me back then!
Travelling in Mexico City - December 2022
Hopefully those civil engineers can work together and come up with a solution because this is a difficult one to solve! This situation demonstrates how important the study of hydrology is when designing for the future :)