In a little more than a year, the place where I stand will be pitch black, lifeless, and full of human waste on bad days. I’m in London’s new super sewer. The sewers are huge concrete pipes that run along the course of the River Thames for about 25 kilometers. It was designed to solve a problem that London and many other cities have been grappling with for decades: the discharge of raw sewage into rivers.
London’s current sewage system creaks at the seams. It was built from 1859 to 1875 after the Great Stink Incident of 1858. At that time, the city had a population of about 3 million. Visionary engineer Joseph Bazalgette designed a sewer system capable of handling a population of 4.5 million and rainwater. With around nine million people now on board, the weather has become wetter and London has been extensively concreted to prevent rainwater from being absorbed by the ground.
The system can no longer keep up. About 60 times a year, the river floods the Thames with a total of 40 million tons of raw sewage per year, plus wet wipes, sanitary napkins, condoms and anything else people deem fit to flush down the toilet. I am throwing it away.
“Our job is to build sewers that address this problem,” says Andy Mitchell, CEO of Tideway, which is behind the project. The answer they came up with was to build a huge overflow pipe deep under the sewers in Victoria to shut off the overflow. Tideway Tunnel is Mitchell said it is one of the largest urban sewerage projects in the world.
It doesn’t solve the problem completely. Discharge still occurs when the rain is very heavy. However, the frequency will be reduced to about 3 to 4 times a year, and overflow will mainly be rainwater. “Bazalgette’s system is full of undiluted sewage,” Mitchell says. “When it rains heavily, that rain flows into the sewers and fills them up. Then they run into the rivers. I catch it.”
We don high-vis clothing, helmets and boots and head to the Access Shaft, a yawning concrete caldera about the diameter of a cooling tower and 50 meters deep. It has to be this big to move a giant boring machine to where the boring work is done.
We climb into a “VIP lift” (actually a metal cage attached to a crane) and slowly lower down. From there we walk through the sewers themselves to get a feel for the scale of this gigantic engineering project. The circular tunnel is 7.2 meters in diameter. Construction took eight years and cost £4.5 billion. The total capacity is 1.6 million cubic meters.
There’s no sewage there now, and the dirty work will start next year, but the tunnels are eerily beautiful, like smooth alabaster in the cold glow of strip lights. “It’s one of his most photogenic tunnels I’ve ever built,” Mitchell says. That’s because it has a serpentine twist that’s strangely pleasing to the eye. It wasn’t planned, but they had to do a “rotate and fill” maneuver to get around the stuck tedious machine and get it out of the way. Baller is now sealed behind a concrete tunnel wall and will be there forever.
The tunnel gently slopes from west to east, a few millimeters per meter. This allows sewage to flow by gravity and does not need to be pumped. “It’s not much, but it’s enough to keep you going,” Mitchell says.
This descent will be up to 55 meters along the length of the tunnel. When the sewage reaches its destination, the Becton sewage treatment plant, it is 80 meters underground and must be pumped. However, the tunnel itself has no moving parts.
The project is expected to be completed in about a year. The lights will be removed, the access shaft will be capped, and the tunnel will remain in solitary darkness for at least 120 years. According to Mitchell, we may be among the last humans to set foot on the ground. Maintenance inspections are carried out by drone. “Technically, it could go down if it needed to,” he says. “But unless restoration takes place, it is highly unlikely that we will go there again.”
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