The History of Sewers
This entry was posted on September 28, 2015.
Many people go about their daily lives without ever sparing a thought for the complex system of pipes and waterways that runs beneath their feet. Without the underground drainage systems that have been developed to serve modern industrialised cities the streets would be polluted by open sewers, with all of the disease and discomfort that this would entail. Think on this the next time that you are sitting outside enjoying a coffee or a snack at a restaurant on one of your town's relatively clean and pleasant streets.
The history of sewerage systems dates back not just hundreds of years, but thousands. The Indus Valley Civilisation, which was located in what is now modern day India, had extremely sophisticated sewerage systems that served their carefully planned cities. These ancient systems were actually more advanced than many in the Middle East and India today. They ensured that every house in the old cities of Harappa and Mohenjo-daro had access to water and drainage.
Later sewer systems were present in ancient Rome, where the Cloaca Maxima took waste water from houses and deposited it into the River Tiber. The Romans regarded this as an engineering marvel. The ancient Chinese also had advanced sewerage systems in a number of their cities.
After the fall of Rome, it took many centuries before sewers in the West reached a similar level of sophistication. Medieval European cities often incorporated natural waterways as a means of draining away waste. London's River Fleet, which ended up being covered over, was an example of a river that became part of a sewerage system.
The modern era effectively began in the nineteenth century when the rapidly industrialising countries of Europe and North America started to experience the consequences of industrialisation in their cities. Britain was the first country to industrialise and was the first whose cities experienced the horrors that massive urban expansion could bring. London in the early 19th century effectively used the River Thames as a huge open air sewer, which caused frequent outbreaks of cholera amongst the local population.
The man who was tasked with solving London's drainage problems and creating a more sanitary city was Joseph Bazalgette. He designed an extensive underground sewerage system that took waste water out into the Thames Estuary, down stream from where the main population lived. This consisted of six interceptor sewers totalling 135 miles in length that took waste from 450 miles of main sewers. The main sewers were in turn fed by 13,000 miles of local sewers. The sewerage system that Bazalgette designed is still in use today.
Mid-nineteenth century sewers tended to discharge waste out to surface water without treatment. As people became aware of the extent to which this practice was causing disease and pollution, cities began to add sewage treatment works to their sewerage systems. These were successful in reducing instances of typhoid and cholera and made a significant contribution to extending average life expectancy in urban areas across the developed world.
In addition to adding ever more sophisticated sewage treatment systems, modern drainage networks separate the sewage from the surface water run-off. This is due to the fact that combined sewers tend to pollute the local water supply whenever there is heavy rain. The surface water in a combined system runs through the same pipes as the sewage which means that an overflow needs to be built in so that in wet weather the sewage treatment equipment isn't damaged by excess water flowing through it. Sewage mixes with the overflow and thereby pollutes the local environment.
Combined sewers are still in operation in many major cities and the pollution from combined sewer overflows has been a topic of growing concern for governments and environmental campaigners. This has resulted in mitigation works being carried out to reduce the ability for combined sewers to pollute the environment during overflow conditions.
One solution that is currently being pursued across the world is sewer separation, where a separate pipeline is laid. However, this is often impractical and expensive in major cities. Another solution is to install combined sewer overflow tanks that can store the excess water following heavy rainfall, and tunnels linking different overflows can also be used for this purpose. Finally, treatment capacity can be expanded in order to handle more of the overflow and reduce the amount that is discharged untreated into the environment.
The constant development of sewerage systems over the past two hundred years has made it possible for people to live healthy lives in our major cities. Increasingly, it is playing a role in ensuring that the wider environment is protected and wildlife is able to flourish.
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