During the Industrial Revolution’s heyday, the Thames was the most polluted river in the world. Now, it’s clean enough for the occasional shark or seahorse, but the waters in London could still be cleaner.

In 2023, sewage was pumped into the London River for almost 10,000 hours, and during storm surges, sewage overflows into the river. Now, after eight years and a £5bn ($6.33B) investment, a new tunnel could solve much of that.

Called the Thames Tideway Tunnel, the 16-mile (25 km) pipe will divert some of the most polluting sewage outflows. Its lid alone weighs 1200 tons.

Finally cleaning up London?

The Thames has been London’s artery since pre-Roman times, but Londoners’ relationship with the river wasn’t always smooth. As early as the 13th century, London’s inhabitants complained about the Thames’ water quality. This prompted city officials to build one of the first organized water systems in the city. It was basically a large pipe that carried fresh water from a nearby spring.

As time went on, sewage pipes were also built. But London has constantly struggled to clean up the Thames — even, to this day. Granted, the Thames has seen some remarkable improvements in water quality, but there’s still a way to go, particularly when there’s a storm.

When existing drains can’t cope with precipitation (usually during storms or periods of excessive rain), the sewage overflow ends up in the Thames. There are also other issues. London’s sewage infrastructure is quite old and requires constant repair. Also, the wet wipes — wet wipes get stuck in sewage once flushed down toilets, and they don’t go away.

A particular issue is “sewage-based wet wipes”, which “enter the river through sewage pipes after they are flushed down toilets”, a spokesperson for the group said. Every few years, workers have to remove bus-sized chunks of wet wipes and other bits that won’t flush.

This is where the new tunnel comes in.

London’s super sewer

The tunnel stretches beneath the River Thames, connecting 34 of the most polluting storm overflow drains and taking them to a sewage plant in east London. Overall, this is expected to reduce the number of sewage discharges from an average of 60 a year to no more than five.

The project is completed over 90% and the tunnel has been sealed off — workers won’t go inside anymore. Trials are set to begin during the summer

Adrian Telford, an engineer on the “super sewer” spoke to the BBC and confirmed that the tunnel will help clean up the river, increase its health, and even reduce some environmental problems like algal blooms. The tunnel is expected to be in operation for over 100 years, with an expected functioning date running up to 2160.

But not everyone is thrilled.

For starters, there’s the cost. The tunnel cost £4.5bn ($5.6B) which will be paid by consumers. However, Lucy Webster, the external affairs director at Tideway, said this would be done gradually, akin to a mortgage on a house.

“What happens is we get private investment upfront, so the investors put money in to enable us to build it,” she said.

“Then bill payers pay for it over time through a contribution from their bills. So, you are spreading that across many, many millions of households and we are able to keep that contribution lower.”

Then, there’s an environmental component.

Not environmental enough?

Initial surveys showed that many Londoners preferred a different, more expensive option — but also more sustainable. This would be a nature-based urban drainage system under Central London streets and open spaces. This would create small pumping stations in key places, along with green spaces that can absorb some of the extra water. It would have also replaced paved, impermeable surfaces with soil, capturing some of the rainwater before it overflows the sewage.

This option would have had the benefit of providing extra green spaces but it would have been substantially more expensive. But supporters of this greener version say the tunnel won’t work as well in the long run. Climate change is expected to bring more intense rainfall to the UK, as well as more storms and extreme weather events.

“The super sewer is a massive, expensive pipe and I think the Victorians would be a bit embarrassed that we haven’t come up with a more modern solution than that,” says Theo Thomas from campaign group London Waterkeeper. “You could use nature to be dealing with this. You could have lots of areas that would soak up the rain rather than rush it off the streets and rush it off the roofs straight into the sewers.”

Ultimately, as cities globally grow and face the escalating challenges posed by climate change, there is a definite need for more substantial, resilient infrastructure to combat pollution and accommodate increasing stormwater volumes. The fight between conventional engineering and modern, nature-based solutions will undoubtedly continue, as both approaches offer unique advantages and face distinct challenges. However, the Thames Tideway Tunnel exemplifies how traditional infrastructure can be leveraged to make immediate improvements while longer-term, sustainable alternatives are explored and developed.

Modern cities must balance the urgency of now with the foresight of tomorrow. This is the only way to remain resilient in the face of a changing climate. This dual approach will likely define the next era of urban environmental management, where the integration of grey and green infrastructure becomes the blueprint for sustainable urban living.