Graph Theory and The Great London Stink of 1858

How a new field of discrete mathematics helped London become less smelly

Keith McNulty

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One July morning in the mid-19th century, the people of London awoke to a disgusting, gut-twisting stench. They couldn’t leave their homes without being sick. The more well-off laced their handkerchiefs with perfume and walked around permanently covering their faces. Many of the poor left town to find work in the countryside because they just couldn’t bear it. It was without a doubt the smelliest incident in British history.

It was the beginning of what became known as the Great Stink of 1858. The River Thames, full to the brim with centuries of human waste that had been dumped directly from the medieval wooden sewer system, was finally getting its revenge. Washed up onto the banks of the river, the cholera-ridden sludge basked in the unusually hot summer temperatures and formed a miasmic stench that was inescapable for miles.

The City of London Corporation — not known at the time for being particularly proactive on public health — realized enough was enough, and invited submissions for the design of a new sewerage plan for the city. The man whose plans were accepted, Joseph Bazalgette, is now considered one of the major civic heroes of London’s past. A talented civil engineer, he oversaw a monumental project of public works which transformed hygiene levels and quality of life in London. Bazalgette’s sewer network is widely regarded as the first step in the creation of the modern city of today, as well as the beginning of the end of cholera in London.

Bazalgette’s sewer network is still going strong, carrying the waste of millions of people eastwards to processing facilities towards the mouth of the Thames. As an engineering project, it was an astounding example of human endeavor: 22,000 kilometers of sewers, 318 million bricks, 2.7 million cubic meters of excavated earth.

Bazalgette was known for how hard he worked himself. He left no stone unturned in making this massive effort future-proof. The gravity and slope of the network to ensure the flow of water, the diameters of the tunnels, all were details he obsessed about. But there were two questions that were crucial to answer at the very outset to make the project…

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Keith McNulty

Pure and Applied Mathematician. LinkedIn Top Voice in Tech. Expert and Author in Data Science and Statistics. Find me on LinkedIn, Twitter or keithmcnulty.org