Aug 9, 2011

7 Wonders of the Industrial World - Part IV

The London Sewerage System

The word sewer means "seaward" in Old English. London's sewers were open ditches sloped slightly to drain human wastes toward the River Thames, and ultimately into the sea. The city of London housed hundreds of thousands of people in crowded conditions and the situation was deteriorating daily. Epidemics of cholera, typhus, "consumption" and other undefined maladies plagued the city over at least four centuries. Sewer ditches quickly filled with garbage and human wastes, which overflowed onto streets, into houses, and into marketplaces throughout London.

With a low population, the waterways were able to absorb the pollution without any serious detriment to the health of the populace, who continued to use the streams and rivers not only as the means of disposing of waste of all kinds, but as a source of drinking water. As London grew in size, however, these waterways became increasingly unable to cope with the associated growth in the flow of sewage, and the sanitary problem became a serious danger to health.

By 1810, the one million population of London was served by 200,000 cess-pits. When cesspits filled to overflow, they were built to drain to the street by means of a crudely built culvert to a partially open sewer trench in the center of the street. The nauseating stench permeated even the most elegant of homes. Indoor odours were often worse than of the garbage- and manure-filled streets.

Methane (swamp) gas generated by cesspits caught fire, exploded and brought instant death to those trapped in sealed homes. Hydrogen sulphide gases overwhelmed victims as they slept, their lungs paralyzed by the gas. Cesspit wastes often soaked foundations, walls, and floors of living quarters. Culverts were frequently blocked causing sewage to spread under buildings and contaminate shallow wells, cisterns and water ways from which drinking water was drawn.

In 1834, John Martin proposed that two intercepting sewers be built below the banks of the river, to terminate at the Tower on the north, and at the Surrey Canal on the south. Two immense receptacles were to be provided, to convert the sewage into manure, and the gas was to be burnt off by huge fires, thus assisting in forced ventilation.

In 1847 the newly-formed Metropolitan Commission for Sewers published a survey of London's sanitary arrangement above and below ground. Amongst other results of this survey was the banning of the use of London's cesspits and the provision of flushing devices to the sewers which carried their contents, untreated, into the Thames. Since drinking water continued to be extracted from the Thames, now converted into an open sewer, typhoid fever and cholera became the two principal scourges of Victorian London.

It is estimated that several hundred thousand Londoners perished from typhoid, cholera, plague and pestilence before it was understood that the city was dying from its own filth.

Part of the problem was due to the introduction of more the modern water closets, or flush toilets. While these were a step forward from the chamber-pots that most Londoners used, they dramatically increased the volume of water and waste now being poured into existing cesspits. These often overflowed into street drains originally designed to cope with rainwater, but now also used to carry outfalls from factories, slaughterhouses and other activities, contaminating the city before emptying into the River Thames.

The crisis came to a peak in the 'Great Stink' of London in 1858. The combination of an unusually warm summer and an unbelievably polluted Thames created a stench of mythic proportions. It was so bad that the curtains of the House of Commons were soaked in chloride of lime in a vain attempt to protect the sensitivities of MPs. A bill was rushed through Parliament and became law in 18 days, to provide more money to construct a massive new sewer scheme for London, and to build an embankment along the Thames in order to improve the flow of water and of traffic.

In 1859, the Metropolitan Board of Works approved a system proposed by its own chief engineer, Joseph Bazalgette to cope with the sewage problem. Constructing this system was a stupendous undertaking, involving 318 million bricks, 880,000 cubic yards of concrete and mortar, and the excavation of 3.5 million cubic yards of earth. The price of bricks in London rose by fifty per cent while it was being constructed.

Eighty-two miles of brick intercepting sewers were built below London's streets, all flowing by gravity eastwards. These were connected to over 450 miles of main sewers, themselves receiving the contents of 13,000 miles of small local sewers, dealing daily with half a million gallons of waste.

Six main interceptory sewers were constructed, some incorporating stretches of London's 'lost' rivers. Three of these sewers were north of the river, the southernmost, low-level one being incorporated in the Thames Embankment. The Embankment also allowed new roads to reduce traffic congestion, new public gardens, and the Circle Line of the London Underground.

The pumping mills, used at various point along the Victorian London Sewerage System, were (and still are) mostly house-like structures where people would work to keep the sewage flowing in the right direction. The sewers were designed to largely run using gravity, but the pumping stations ensured that in areas the needed it, the water and sewage levels were raised to keep it flowing towards the east.

There was no attempt to treat the raw sewage: Bazalgette believed that the drainage of the low-lying land in London was more important than cleansing the Thames. There were, of course, other regulations made concerning the supply of clean water to London at this time, but without Joseph Bazalgette's magnificent scheme, these would not have begun to deal with the essential problem - the appalling contamination of the River Thames. The success of these measures can be gauged by the fact that there was just one final outbreak of cholera in London in 1866 - just one year after the pumps were started at the opening ceremony.

Considering that the system was built during the wettest summer and the coldest winter recorded in the nineteenth century, it was an astounding achievement, even for Victorian civil engineers.

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