In simply over a yr’s time, the place I’m standing can be pitch black, devoid of human life and – on a nasty day – filled with human effluent. I’m in London’s new tremendous sewer, a monstrous concrete pipe that runs roughly alongside the course of the river Thames for 25 kilometres. It’s designed to resolve an issue that London and lots of different cities have been grappling with for many years: the discharge of raw sewage into rivers.
London’s present sewage system is creaking on the seams. It was constructed between 1859 and 1875 after the Nice Stink of 1858. On the time, town’s inhabitants was round 3 million. The visionary engineer Joseph Bazalgette designed a sewer to deal with 4.5 million folks plus rainwater. Round 9 million now use it, the climate is wetter and London has been extensively concreted over, stopping rainwater from being absorbed by the bottom.
The system can now not cope. Round 60 instances a yr it overflows, dumping a complete of 40 million tonnes of uncooked sewage per yr into the Thames plus moist wipes, sanitary merchandise, condoms and no matter else folks see match to flush down the john.
“Our job is to construct a sewer that can deal with that,” says Andy Mitchell, CEO of Tideway, the corporate behind the undertaking. The reply they got here up with was to construct a big overflow pipe deep underground, beneath the Victorian sewer, to intercept its overflows. The Tideway Tunnel is one of many greatest metropolis sewer initiatives on this planet, says Mitchell.
It received’t clear up the issue utterly: when the rain is basically heavy there’ll nonetheless be discharges. However it’ll scale back their frequency to round three of 4 instances a yr, and the overflow can be predominantly rainwater. “The Bazalgette system will get filled with undiluted sewage,” says Mitchell. “If it rains closely, that will get channelled into the sewers, and the sewers get full. They then flush into the river. But it surely’s that first flush, which is pure sewage, which is probably the most damaging. We seize that.”
We package ourselves out in high-vis clothes, onerous hats and boots and head to the entry shaft, a yawning concrete caldera concerning the diameter of a cooling tower and 50 metres deep. It must be this huge to get the large boring machines all the way down to the place they do their boring stuff.
We clamber into the “VIP carry” – truly a metallic cage hooked up to a crane – and are gently lowered to the underside. From there we stroll down the sewer itself to get a really feel for the dimensions of this colossal engineering undertaking. The round tunnel is 7.2 metres throughout. It took eight years to construct at a price of £4.5 billion. Its complete capability is 1.6 million cubic metres.
There is no such thing as a sewage in there now – the soiled work begins subsequent yr – and the tunnel is eerily lovely, like easy alabaster within the chilly glow of the strip lights. “This is likely one of the most photogenic items of tunnel I’ve ever constructed,” says Mitchell. That’s as a result of there’s a sinuous kink that’s oddly pleasing to the attention. It wasn’t deliberate however they needed to skirt round a boring machine that grew to become caught, doing a “flip and bury” manoeuvre to get it out of the way in which. The borer is now sealed behind the concrete tunnel wall and can be there endlessly.
The tunnel slopes gently down from west to east, a number of millimetres each metre. That allows the sewage to stream by gravity, no pumping required. “It doesn’t sound a lot but it surely’s sufficient to maintain it shifting,” says Mitchell.
This descent provides as much as 55 metres alongside the size of the tunnel. When the sewage arrives at its vacation spot, Beckton Sewage Remedy Works, it’s 80 metres underground and must be pumped again up. However the tunnel itself has no shifting components.
In round a yr, the undertaking can be full. The lights can be eliminated, the entry shafts capped and the tunnel plunged into lonely darkness for at the least 120 years. It’s doable that we’re among the many final folks to set foot in it, says Mitchell. Upkeep inspections can be carried out by drone. “Technically we might go down if now we have to,” he says. “However until there’s a restore, which is very unlikely, we’re unlikely to ever go down there once more.”
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