by Roma Agrawal
Thomas McLean’s etching ‘Monster Soup commonly called Thames Water’ of 1828 was a grotesque satire on the city’s water supply.
That London’s waste was ruining the capital became particularly apparent during the unusually hot summer of 1858, which warmed up the banned but festering cesspits and the sewage-filled Thames and its tributaries, so that the city smelled even more horribly pungent than usual. And so the ‘Great Stink’ (as it was called) began. It became so unpleasant that people soaked their curtains in a lime chloride mixture to try and hide the stench. The smells were so noxious that ministers working in the House of Commons, and the lawyers at Lincoln’s Inn, were unable to work, and they made plans to abandon the city.
The only upside of all this was that, having been affected by the awful conditions first-hand, the government finally became determined to get rid of the stench and the cholera that came with it. In 1859, after years of rejecting plans from engineers to solve the sewage problem in London, officials finally approved the works proposed by Joseph Bazalgette.
Bazalgette was described as having an indifferent temperament but a pleasant and genial smile. He was considerably below average height but his long nose, keen grey eyes and black eyebrows gave him the impression of being a powerful man. He was born in Enfield on the outskirts of London in 1819 and pursued a career as a civil engineer. A taxing stint working on the rapid expansion of the railways led to a nervous breakdown in 1847, after which he became a surveyor for the Metropolitan Commission of Sewers, tasked with solving the problem of drainage in London. He was later appointed to the Metropolitan Board of Works, whose job it was to devise a solution to London’s problems with waste disposal.
Bazalgette’s plan made use of the Thames’ old tributaries, which were now basically sewers, and which had been diverted to flow along brick culverts or channels. The diversions helped to satisfy the demand for more housing: restricting the rivers to narrow culverts allowed people to build homes close to the edge of the water. These culverts were often buried under roads, freeing up even more space. Their highest point was away from the river, and they flowed down in a north–south direction until they reached the Thames (which flowed west to east), where they deposited their putrid water.
Joseph Bazalgette decided he would intercept these culverts and their horrible contents. He did this at various points, creating a web of new sewers that sat below the old culverts. Inside these old culverts, to partially block the water flow, he constructed weirs (a form of water barrier) that were half as tall as the height of the culvert. Then, in front of these weirs, he bored holes through the floor so that most of the waste water would be redirected into his new sewers below. Hold up your left hand with your fingers spread out, then put your right hand below it at right angles to the left, and you’ve got a good representation of Bazalgette’s system. Your left hand is the series of old tributaries flowing through their culverts; your right is Bazalgette’s new sewers.
North of the river, Bazalgette installed sewers below the culverts at three points. The first was far north, where the culverts were relatively high (for those familiar with London, this branch runs from Upper Holloway through Stamford Hill and Hackney down towards Stratford). About halfway between this ‘high-level’ sewer and the river, he installed a ‘mid-level’ sewer, running from Bayswater, below now world-famous shopping area Oxford Street, and Old Street. This collected more of the wastewater as it hit the weirs and poured down through the holes in the base of each culvert. Finally, very close to the river, he put in a ‘low-level’ sewer to capture the remaining water. South of the river he did something similar but used only a high-level sewer (running from Balham through Clapham, Camberwell and New Cross to Woolwich) and a low-level one (going from Wandsworth through Battersea, Walworth and on to New Cross). This was because there were fewer people living there, and the extent of the city south of the river was less than in the north. In total, this system, end-to-end, would have measured 160km.
Bazalgette’s main sewer network that reached across London.
The Victoria, Albert and Chelsea embankments in London are all products of his work. These contain the low-level sewers that run alongside the River Thames. Just as engineers before him had restricted the width of the tributaries of the Thames by putting them in culverts, Bazalgette narrowed the mighty river itself with these embankments. His new underground routes not only housed the new sewers, but also created space for the first underground railway: the London Tube.
When designing the five main sewer pipes and the hundreds of offshoots, to calculate the size required Bazalgette made a generous allowance for the amount of waste produced by every one of the 2 million inhabitants of the city. Then, figuring that these sewer constructions would only be done once, he doubled the size. His five sewers were at their highest point where they began in the west, and they sloped two feet for every mile as they travelled east towards two new pumping stations. Designed by Bazalgette and the architect Charles Henry Driver, these were Crossness (which served the two southern sewers) and Abbey Mills (which served the three northern ones). Solid, imposing and cathedral-like, both pumping stations are masterpieces of late-Victorian architecture. The real surprise is the interior of Crossness, in which the vast pump machinery is surrounded by gleaming brass and extravagantly ornate, colourfully painted wrought ironwork. In fact, the stations have appeared on screen several times, notably in films such as Batman Begins and Sherlock Holmes.
The interior of the Victorian pumping station with its decorative ironwork at Crossness Sewage Treatment Works, Erith, London.
Having travelled through the sewers and reached the pumping stations, the waste had to be lifted back up to a level high enough that it could flow naturally to large sewage storage tanks further east. North of the river, the waste was stored at Beckton, while south of the river it was stored in a tank next to the Crossness pumping station. The reason the waste needed to be raised was so it could flow under gravity into the Thames when the river flowed out towards the sea on its ebb tide. At this time, the contents were still being dumped into the river untreated.
Bazalgette was told to make sure his tanks were far enough east so that, in the worst case, if they had to be emptied during an incoming tide because they were full, the back-flowing sewage wouldn’t come as far west as Westminster – the ministers didn’t want a repeat of the smells they experienced in 1858. In fact, by narrowing the river, Bazalgette inadvertently caused its tidal range to go further back than before, so occasionally the smells did get quite fusty.
Although the idea behind Bazalgette’s sewage system was in essence quite simple, executing it was not, as building the new sewers meant digging up London’s roads. It must have been an incredibly invasive and complex piece of work, digging down to the right level, constructing egg-shaped brick sewers and the connections to the culverts, then filling the hole and redoing the roads. But it was worth it, because life in the capital slowly began to get better.
The quality of water in central London improved dramatically. Bazalgette’s sewers (2,100 kilometers of them, made up of more than 300 million bricks) were finally completed in 1875. By that time, the ravages of cholera in London were a thing of the past, in large part due to Bazalgette’s practical, efficient and imaginative piece of engineering.
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Bazalgette took the sewage from central London and deposited it outside the city into the River Thames, which ultimately took it out to sea. The waste was not treated, so the system basically moved the disease-causing elements from a populous area to a deserted one. If this sounds to you like a somewhat old-fashioned approach, then it may come as a surprise to learn that we use exactly the same system today.
Nowadays, in new waste systems, the water collected from rainwater goes ideally into pipes that are separate from those that pick up sewage from homes and offices and industrial waste from factories and restaurants. The idea is that the rainwater, which is not polluted, can be discharged into seas o
r rivers, while the sewage and industrial waste are taken to treatment plants.
At the plants, the polluted waste is broken down into its base chemicals, using a series of physical, chemical and biological processes. ‘Physical’ could mean filtration: passing water through membranes to remove impurities. ‘Chemical’ is the addition of substances to the waste, which react with it to break it down. ‘Biological’ is a similar process, but using bacteria to break down the waste. The aim is to create ‘treated effluent’ – an environmentally safe fluid for disposal – or ‘sludge’, solid waste that can also be disposed of or used as an agricultural fertiliser.
That, at least, is the theory. In practice, it rarely works like that. Shockingly, estimates by UN-Habitat (an agency monitoring places where people live) state that, globally, 90 per cent of waste water is released into the environment untreated or after only primary treatment. And at the moment, London is no exception. This is because Bazalgette’s sewers are ‘combined sewers’, which means that they carry everything – rain, sewage, industrial effluence. Bazalgette was incredibly forward-thinking in designing the sewers for the waste of 4 million people (twice the population of Victorian London) plus rainwater. Now, though, the population in London is 8 million and we are still using this system, which is nearly 150 years old. The reason it still works most of the time is because the sewers are big enough to cope with the 1.25 billion kilograms of poo they receive each year. But since the system is working at relatively full capacity, it can’t cope with rain as well, so even if it rains just 2mm in a day (which is a common occurrence in dear, damp London), these combined sewers fill up and overflow.
Dotted along the sides of the River Thames are 57 pipes that discharge this overflowing waste directly into the river. You can see the exit point for one of these at Battersea, where there is a large, reinforced iron door set into the river bank; there’s another under Vauxhall Bridge. The Vauxhall one alone currently releases 280,000 tonnes of waste a year. Some of these exit points were built in Bazalgette’s times, while others were added later. In 2014, excess flow had to be discharged into the river more than once a week, equating to 62 million tonnes of untreated sewage released into the Thames every year. That’s the equivalent in weight of more than 8,500 blue whales plunging into the river every week. If we do nothing, that will almost double by 2020. Such statistics are liable to make anyone breathe uneasily. Fortunately, however, between now and 2023 a huge project to deal with this problem will be under way, under the feet of unsuspecting Londoners: the Thames Tideway Tunnel.
I made an appointment to see Phil, one of the directors of the project to create a new ‘bowel’ for the capital. We settled down in a large canteen to chat about urine and faeces – or, more specifically, how they will now be removed in a more modern manner.
‘Our scheme is an extension of Bazalgette’s legacy,’ Phil explained. ‘One that, I believe, he would have done himself if London’s population had grown to such extents during his lifetime.’ The premise of the project is simple: 150 years ago, Bazalgette intercepted the decaying tributaries. Now, the Tideway Tunnel will intercept Bazalgette’s sewers: instead of the wastewater from his sewers overflowing into the river, it will overflow into a new network of tunnels.
The scale of the project is impressive. At 21 sites around the city – including one at the Vauxhall discharge point – new vertical, cylindrical shafts will be dug up to 60m deep to collect the excess sewage. Most of these will be built at the edge of the river. The first step is to build a large cofferdam, a watertight enclosure where the construction site can be set up. Within this area, a new shaft will be installed close to the existing sewage discharge point. Chambers will then be built to connect the existing discharge point to the shaft. So, instead of flowing into the river, the sewage will flow through the chambers into the new shaft. As Phil pointed out, while it’s fine providing a new system, it’s also extremely important that it’s invisible, both to sight and smell (I pictured living next to a large toilet). Acres of public gardens and parks will be developed on top of these shafts. So in a few years’ time, you’ll be sitting on a bench by the river sipping your cappuccino, surrounded by grass and trees, while literally tonnes of sewage per second pour from Bazalgette’s sewers into the shaft below you. When the waste reaches the bottom of the vertical shaft, a pipe will carry it through to the new tunnel.
Intercepting sewage via the planned Tideway Tunnel; the future of the sewage system within London.
This main artery is 7.2m in diameter: large enough to contain three double-decker buses side by side. It starts at Acton in West London and falls 1m for every 790m that it runs east. By the time it reaches the pumping station at Abbey Mills, the tunnel is as deep as a 20-storey building is tall. From Abbey Mills, the sewage is pumped to the Beckton sewage treatment works.
The majority of this tunnel runs below the River Thames in central London, which is a really interesting engineering strategy. It’s an excellent idea to do this, because running new infrastructure under a busy city is difficult at the best of times. But London in particular has a large underground tunnel network and thousands of buildings with deep foundations. By running the tunnel below the water itself, it passes under only 1,300 buildings (which might seem a lot until you consider how many more it would have been if the tunnel had run under land instead). It also goes below 75 bridges and 43 tunnels, including the Tube tunnels, as it burrows under the city.
The ground itself poses another huge challenge. Since the tunnel runs across the city, and slopes downwards from west to east, it encounters different soil at different places. At the start in Acton it goes through clay, which is prone to expanding and contracting. In the middle section, through central London, it runs through mixed sands and gravels, which are problematic materials to tunnel through because they move around and aren’t cohesive. Finally, in the east, in Tower Hamlets it runs through a chalk layer with big chunks of flint in it. It’s impossible to predict where all this flint will be, and, because it’s difficult to cut through, it can cause delays as the tunnel boring machines (TBMs) struggle to slice their way through the ground. The tunnel needs to be strong, especially at the junction between two different types of soil, because one type of soil might be much more cohesive or drier than the other, and apply different forces to the tunnel as it expands and contracts. Five TBMs will work at the same time in different parts of the city, moving in different directions, to form tunnels that will eventually join up to create the ‘super sewer’.
The aim of this mind-boggling project is to bring down the number of discharges into the river from 60 a year to four, reducing the amount of wastewater from 62 million tonnes to 2.4 million tonnes a year. I asked Phil why the discharges couldn’t be completely stopped, and he explained that these four discharges would happen only when there is very heavy rain: during such storms, the sewage is diluted considerably as the storm water mixes with the waste, so the discharge into the river is not toxic. The oxygen levels in the river would not really be affected by these diluted overflows because of the natural biological processes in the water that maintain its ecosystem. To reduce the discharges to zero, the Tideway Tunnel would have had to be twice as big.
Engineers often need to compromise in this way: the ideal solution is not always the most practical one. Ideally, we would have separate sewer pipes for rainwater and for waste, but this would mean having to more or less shut down London and dig up all the streets to put in a brand-new system. Even more ideally, we wouldn’t discharge into the Thames at all, but this could actually be worse for the environment. Creating a tunnel of the necessary size would mean removing twice as much soil from the ground, resulting in a much longer construction process with bigger machines and much more energy. This method would also reduce the amount of water in the river itself, as the flow of the natural tributaries would be completely shut off.
The Thames Tideway Tunnel project will clearly have a momentous effect on the quality of the river: n
o longer will swimmers and rowers have to worry about sloshing through human waste. But what made me even happier was when Phil pointed out that the project will incorporate new treatment plants. We’ve come full circle from Bazalgette’s solution, and are adding another network of shafts and tunnels to his system to meet the needs of the modern city. But this time we will be decontaminating our waste so we don’t contaminate our seas.
Today, we pay homage to Bazalgette for having the skill and imagination to create a sewer system we are still able to use, 150 years later. Hopefully, the current expansion of the system will serve us just as long and, in a century’s time, city dwellers will be thanking us for giving London a new bowel.
That’s probably enough about poo.
IDOL
When I walk into a room for a meeting, I’m often the only woman there. Sometimes I keep a tally – 11 men and me, 17 men and me. The most, I think, was 21 men and me. Surrounded by men, I conduct my business, bemused when one of them swears, then looks sheepish and apologises directly to me (they’ve clearly never seen me driving my car in heavy traffic). I have opened countless work-related letters addressed to ‘Mr Agrawal’ – after all, if you can’t tell my gender from my name, you have a greater than 90 per cent chance of being right if you go for male. Because, much to my frustration, I am in a minority in my profession.
Working in a man’s world can be challenging in all sorts of ways, sometimes comical, other times trying. It’s hard to keep a straight face and conduct professional conversations about finite element modelling or soil strength profiles when I’m in a site office surrounded by pictures of naked women. On one occasion a builder asked me if I wanted my picture taken in my ‘costume’, in other words, the hard hat and hi-vis jacket I wear regularly for all the site visits that are part of my job. I’ve heard stories from other women in the industry about how they’ve been (illegally) asked in job interviews when they plan to get married and have children.
