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05 October 2017

London's Super Sewer: Getting To The Bottom Of It

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11 September 2017: Thames Tideway workers commence digging a new shaft at Battersea from which Tunnel Boring Machines will set out to construct London’s new ‘super sewer’. It would be possible to put the dome of St Paul’s Cathedral down the shaft when it is complete.

If you stand on the roof of Battersea Power Station today and look east, you can see a massive boxy shed being erected. This will contain the noise and dust from a huge excavation which will see mighty tunnel boring machines set off beneath the river to create London’s new ‘super sewer’, the Thames Tideway. If you look south you can see another huge work area from which more boring machines have recently set out to construct the Northern Line Extension, a new Underground line to the Power Station.

The underlying reason for all this tunnelling is more people. London’s population has recently hit an all-time record at more than 8.5 million, and this naturally means a need for more transport and underground rail lines. More people also need more showers, more dishwashers and washing machines, more sinks. They need more ground covered by buildings and roads and car parks and so on, which means more drains. All of that means more and more dirty water, all needing to be dealt with effectively.

Not to put too fine a point on it, more people also generate more poo: which is significantly nastier and more dangerous than dirty water, though in London (as in most old cities) the two problems have always been handled by the same pipes. These issues have been around ever since cities were built, in fact: the Cloaca Maxima ('Great Sewer') of ancient Rome is thought to have been in use long before the Emperors, before even the old Republic, from the almost prehistoric era of the early Roman kings.

London was also a Roman city later on, and the Romans are thought to have given it some of its earliest sewers. They certainly built sewers in other British towns, for instance Eboracum – today’s York – where some of the Roman sewer network was discovered intact in 1972. These Roman sewers in Britain, like the Cloaca Maxima, actually dealt mainly with used water from the communal baths that the Romans regarded as an essential element of civilisation.

For a long time after the Romans left, the British didn’t regard baths as being terribly important: but they still needed to get rid of rainwater to avoid flooding, and London like other cities had drains and sewers built mainly for this purpose. These generally emptied into the Thames. As early as 1531, King Henry VIII found it necessary to provide some regulation and oversight of his capital’s sewerage, and he issued the Bill Of Sewers that year. The Bill set up eight different groups of commissioners and charged them with keeping the sewers in their districts in good repair, but there was no central authority and this meant that there were no common standards and no single map on which you could find all the city’s sewers.

As for the poo, a lot of it always did find its way into the London sewers by one means and another: but right into the 19th century cesspits remained in common use, meaning that the sewer water was not as unpleasant and unhealthy as it later became. But the cesspits caused awful smells and health problems, and were also subject to build-ups of flammable gas: they sometimes caused particularly disgusting explosions and fires. Early in the 19th century, new regulations decreed that all new buildings would have sewer connections rather than cesspits. The increasing popularity of flushing lavatories also led to more and more human waste going into the sewers: the famous Thomas Crapper, later to become purveyor of sanitary plumbing to the royal family, began his career in 1853. London’s burgeoning population – in the mid-19th century rising through three million – added to the problem.

By the 1850s the situation had become dire. The River Thames had effectively become a giant open sewer. Its powerful tides served to carry the excrement upriver as much as they took it out to sea, and some of the city’s water supplies were then drawn from points surprisingly far down in the tidal reaches. One example was the Battersea Fields waterworks, on whose site Battersea Power Station was later built, which supplied water described by the biologist Arthur Hassall in 1850 as 'the most disgusting which I have ever examined'.

This contamination of drinking water caused the frequent and deadly cholera outbreaks which plagued London in those days, though this was not understood at the time. The pioneering doctor John Snow had theorised that cholera was carried by drinking water in 1849, but it would take many years for the medical establishment of the day to accept this. Fortunately, as it turned out, the prevailing scientific belief was that disease was the result of bad smells or 'miasmas': and the increasing amount of human waste in the Thames was causing something quite special in this line. Public pressure to clean up the river began to build, assisted by the then widely accepted scientific fact that its terrible stench was actually causing the cholera outbreaks.

The Great Stink

Matters came to a head in 1858, when London suffered an especially hot, dry summer. Lack of rain caused the level of the river to fall so that sewage was washed away even less efficiently, and the thick layers of mixed sewage and mud exposed at low tide baked in the 36°C heat. The resulting awful stench became known as 'the Great Stink'. Fortunately for the people of the city, nowhere was worse affected than the Houses of Parliament on the river bank at Westminster: desperate politicians had the curtains of the riverside windows soaked with lime chloride, but this had little effect.

Properly speaking the national government was not in charge of the River Thames, of course: but there was now an organisation that was. Henry VIII’s disorganised sewer commissioners had finally been replaced, after more than 300 years, by the short-lived Metropolitan Commission of Sewers in 1848. This in turn gave way to the Metropolitan Board of Works in 1855. These bodies may in fact have worsened the state of the Thames by their efforts to eliminate the unhealthy cesspits and to flush through the existing smelly sewers with water on a regular basis: they had plans to deal with the river too, but lacked the money and authorisation to carry them out.

The Great Stink and its effects on Parliament provided both. In June of 1858, the new Chancellor of the Exchequer, Benjamin Disraeli, put through a bill ordering the Board of Works to clean up the Thames and move all sewage discharge out of the city. The Board was authorised to borrow the necessary millions of pounds and repay the loans by collecting a threepenny levy from all London households for the next forty years.

The chief engineer of the Board of Works was the great Joseph Bazalgette, who had been working on his plans for the city’s sewers for almost a decade by this point. Now, at last, he was able to carry them out.

Bazalgette’s plans called for two mighty Outfall sewers to the east of the city on either side of the Thames, which would carry the sewage to huge storage reservoirs at Beckton and Crossness. Here it could be safely released out to sea on the ebbing tide. These Outfalls would be fed by massive sewer lines running broadly west to east across London: those further from the river were set at higher levels to collect the waste from the northern and southern suburbs, generally on higher ground. The construction of these mid-level and high-level sewers was a relatively simple matter.

The difficult part of the scheme was the capture of all the effluent flowing into the Thames in the heart of the city. Bazalgette solved this problem in large part by building out into the river. He created the Victoria, Chelsea and Albert Embankments and built massive low-level sewers inside them, into which all the previous sewer outlets now flowed. Instead of going into the Thames, the sewage now travelled eastwards alongside it. The embankments also provided useful new roads, and in the case of the Victoria embankment, a new underground railway line as well. The Northern low-level sewer leaves the riverside at Blackfriars and continues eastwards below the City and the East End: a century and a half later the Crossrail tunnellers had to be careful to go beneath it.

‘The Cathedral Of Sewage’

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The Abbey Mills sewage pumping station. Nothing dull or utilitarian there.

Bazalgette’s higher-level and low-level main sewers all came together at Stratford to the north of the river and Deptford to the south, where the huge multi-tunnelled Outfalls began. But the need to provide a downward slope in the tunnels to keep the sewage flowing along meant that the outlets of the feeding sewers were much deeper down than the start of the Outfalls. This was dealt with by the construction of powerful pumping stations, driven by huge steam engines, which lifted the sewage up into the Outfalls. These pumping stations, in the manner of their time, were ornately decorated: the northern Abbey Mills station was dubbed the 'Cathedral of Sewage' and both are now listed heritage buildings. Strong approval for the sewage project was evident. Queen Victoria was only prevented by illness from presiding over the opening of the Victoria Embankment (the Prince of Wales stood in for her) and the sewage pumping engines at the southern station were all named after members of the royal family.

Bazalgette’s mighty scheme was finally completed in 1875 after sixteen years of construction: he was knighted in 1874. The work had required 318 million bricks and more than half a million cubic metres of concrete and mortar: altogether it had cost the then-staggering sum of £6.5 million. Though the prevailing theory that cholera was caused by bad smells had been wrong, the sewage project nonetheless eliminated the cholera threat by moving human wastes away from the water supplies. It has been estimated that Bazalgette did more good and saved more lives than any other single Victorian official: and he made the city smell better too.

Future Proofing, Victorian Style

Bazalgette’s great scheme has remained the backbone of London’s sewers to this day, though various changes and additions have been made. The long service of the works is partly due to the fact that they were very well constructed, with much innovative use of long-lasting Portland cement, subjected to very stringent new tests devised by Bazalgette before being used.

The other reason that the scheme has served so well and so long was that Sir Joseph famously calculated the maximum possible population the area could hold, assumed the largest possible amount of resulting sewage and worked out the diameter of tunnels required. He then said ‘we're only going to do this once and there's always the unforeseen’, and doubled the diameter of his conduits.

This decision meant that the sewers not only coped with London’s population rising faster than had been forecast at the time – it had passed four million by the time the works were complete – they did far better, even surviving the appearance of tower blocks in the 1960s. But even Bazalgette’s system couldn’t be expected to remain sufficient forever, and today’s record London population is too much for it. There’s no risk of cholera returning, as water is now taken from safe places and intensively tested, but the Thames is now being polluted with large amounts of untreated sewage once again.

This isn’t, in fact, entirely a matter of more people: London has had a population above 8 million before, in the 1930s and 1950s. Today it has even more, over 8.5 million, and they use a lot more water than Londoners used to, but that isn’t the whole story. Today the city also has more built-up area and less green space, which means more water runoff. When heavy rains fall on London, even Bazalgette’s mighty sewers can’t cope with the huge amounts of combined runoff and sewage. To prevent them backing up into people’s homes, they were built from the start to overflow into the Thames. When they were completed, this would happen perhaps once or twice a year: nowadays it happens on average once a week. Overflow events can now be triggered by quite mild rains.

These days when people build a brand-new city this sort of thing isn’t a problem, as sewage and rainfall are handled by separate systems. But separating all of London’s waste water systems along modern lines would be a truly colossal project: it has been estimated that the cost would be £50bn to £60bn at today’s prices.

A new ‘super sewer’ for London

Instead it has been decided to adopt the solution that Sir Joseph himself would probably have chosen: build another tunnel to catch the overflow and pipe it east – these days to be treated and cleaned before release, rather than simply dumped raw into the Thames Estuary at high tide. It’s not really feasible to build out into the Thames again as Bazalgette did, so this time the tunnel will run deep down beneath the river bed.

When the old sewers overflow, as they now do so regularly, they will overflow into new shafts and pipeways down into the new Thames Tideway tunnel, not into the river. This new tunnel will run beneath the river from Hammersmith in the west to Tower Hamlets in the east, before heading north to the Abbey Mills pumping station. Here the sewage will move on out of the city to the east, but not via Bazalgette’s Northern Outfall: the Outfall has been badly overloaded for a long time, causing major sewage overflows at Abbey Mills. As a result the Lee Tunnel, running deep beneath the Outfall from Abbey Mills to the treatment plant at Beckton, has already been in operation since 2016. It was deliberately bored deep down so that the new Tideway Tunnel can connect up to it, and through it the sewage will flow on to Beckton where it will be pumped up to the surface and treated.

The new Tideway Tunnel, also known as the ‘super sewer’, is expected to cost £4.2 billion. The equivalent cost of Bazalgette’s sewers would be £729 million if we account for inflation since the 1860s, so the Tideway will cost almost six times what the Victorian sewers did. However, household incomes have multiplied over the last century and a half, probably by more than sixfold in many cases: it seems fair to say that the cost of the Tideway on water bills will hit Londoners on average less hard than the Board of Works’ threepenny levy did in the 19th century.

Work on the super sewer is under way. One of the sites from which the Tideway boring machines will set out is at Battersea Power Station, close to the actual Power Station building which is now being restored and redeveloped as a mixture of homes, shopping and offices. When the tunnelling is complete, further mixed-use development will appear on top of the current Tideway works area, and there will be a new Underground line close by – just as the new buildings and roads of the Embankment appeared atop Bazalgette’s sewers, and a new Underground line ran alongside them.

So the story of the city and its sewers moves on: and oddly enough this particular London story also began here. Battersea Power Station was originally built on the disused reservoirs of the Southwark and Vauxhall Waterworks Company, whose 'most disgusting' and unsafe water provided much of the impetus which made Bazalgette’s plans a reality.

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