Thames Tideway 'super sewer' infrastructure must provide a blueprint across the UK

14 mins read


The tunnel’s diameter is as wide as three London buses side by side

The tunnel’s diameter is as wide as three London buses side by side (Image: Jonathan Buckmaster)

The heavy stainless steel box, attached to breathing apparatus, provides 30 minutes of oxygen and is obligatory for visitors to the Thames Tideway Tunnel – otherwise known as London’s “super sewer” – being built beneath the capital.

BOWELS OF THE EARTH: Cross section of the Thames Tideway Tunnel

BOWELS OF THE EARTH: Cross section of the Thames Tideway Tunnel (Image: Jonathan Buckmaster)

This is because it’s considered too risky for ordinary firefighters and paramedics to reach people below ground in an emergency.

But John Clifton, a section manager for the tunnel’s west section and my chaperone, assures me it’s not been necessary to activate a single tank since construction began in 2016, which is a relief.

Despite that reassurance, I have a newfound respect for the thousands of workers who have toiled in such challenging conditions for the past six years.

After a summer of heatwave and drought – and growing complaints that privately-owned water companies have not invested enough to tackle leaks or increasing capacity while draining billions of pounds of profits from customers – the £4.3billion, 16-mile tunnel is one of the biggest infrastructure projects ever undertaken in Europe.

Once it opens for business in 2025, it will dramatically reduce sewage overflows into the Thames by providing storage and outflow for the capital’s creaking sewerage systems, especially when they are overwhelmed by stormy weather.

With added encouragement coming from Downing Street’s new resident, it will also, hopefully, be the blueprint for further massive investment in the country’s ageing water infrastructure.

Campaigner Ash Smith from Windrush Against Sewage Pollution said: “Any major investment is welcome. There is an absolutely desperate need because of years of under-investment.”

Kat Hopps visits the tunnel

Kat Hopps visits the tunnel (Image: Jonathan Buckmaster)

Mr Smith urged privatised water giants to invest more of their profits into improving infrastructure, rather than in shareholder dividends or pay rises for bosses.

Currently, more than 40 million tonnes of sewage are released into the Thames each year.

That’s 50 individual spills a year, a picture reflected nationwide as the dumping of raw sewage into our rivers and lakes by the various private water companies has risen 29-fold over the last five years.

As we descend, a statue of Saint Barbara, the patron saint of tunnellers and miners, keeps a protective eye over workers from a wooden box at the side of the shaft.

“It’s a reminder that this isn’t a walk in the park,” explains Roger Bailey, chief technical officer at Tideway, the company managing the super sewer project.

“When you go down a tunnel and see Saint Barbara, you think about the risks as it is very much a life and death scenario. It’s a spiritual thing, and if that helps people and reminds them to be careful and look out for each other then that’s great.”

Father Bill Bowder from Our Lady of Perpetual Help in Fulham, west London, blessed the statue as tunnelling began.

The Catholic priest wore full robes for the ceremony but not PPE (health and safety regulations need not apply if you are afforded the protection of a higher power). Thankfully there have been no fatalities.

Father Bill Bowder blessed the statue

Father Bill Bowder blessed the statue (Image: Jonathan Buckmaster, Getty)

“We have a good safety record so far but we are by no means complacent,” says Roger.

I am at Carnwath Road Riverside, the tunnel’s westernmost section at Wandsworth Bridge, Fulham, because London has been battling a super-sized, stinky problem.

The current 150-year-old sewer system, containing 1,100 miles of drains, was built to serve a mere four million people but now caters for nine million Londoners.

“What that does in terms of the ecology, wildlife, litter, pathogens in the river for rowers and other people engaging in leisure activities is quite disgusting,” says Roger.

“Time of the year, water temperature, fluvial flow can all conspire to create a really serious environmental incident if they happen at the wrong time.”

Part of the problem is the increasing rainfall caused by climate change. Inner London runs on a combined sewer system that carries wastewater from homes and run-off rainwater from roads and gardens.

During heavy downpours when the system becomes overwhelmed, valves are opened into Combined Sewage Overflows (CSOs) feeding directly into the Thames. This prevents sewage from backing up into homes and businesses.

The sewer’s creator is the Victorian engineer Sir Joseph Bazalgette

The sewer’s creator is the Victorian engineer Sir Joseph Bazalgette (Image: Jonathan Buckmaster, Getty)

The sewer’s creator, the Victorian engineer Sir Joseph Bazalgette, could never have envisaged the city’s incredible growth – nor how people would pave over gardens for drives, thus reducing ground space where rainfall can be absorbed. “The actual Victorian infrastructure is in a remarkably good condition and is working remarkably well,” explains Roger.

“But because there are so many people in London now, and the storm capacity in those sewers is reduced because of other factors, as little as two millimetres of rain can cause it to overflow.”

This explains the need for the UK’s largest ever water infrastructure project. The tunnel stretches from Acton, west London, to Abbey Mills Pumping Station, in the east of the capital, where it connects to the Lee Tunnel servicing Beckton Sewage Treatment Works, taking sewage from the worst-affected CSOs.

Once opened in 2025, it should prevent 94 percent of sewage overflows and reduce spills to fewer than five a year. Tunnelling was completed in April and Thames Water is due to begin test flows shortly.

My visit starts in the acoustic shed, a large warehouse where one of 21 gigantic shafts has been excavated along the length of the tunnel to allow access and machinery. Noise and light pollution are blocked out, allowing operations to run day and night.

An external shutter closes at 6pm and the interior is illuminated by floodlights, making it as bright as a lit football stadium. Peering over the shaft is not for the faint of heart. John, my guide, describes it as a “manhole similar to what you would find at the bottom of your garden…but on a bigger scale”.

Cavernous world of cathedral-like proportions

Cavernous world of cathedral-like proportions (Image: Jonathan Buckmaster, Getty)

Descending by a lift, we enter a cavernous world of cathedral-like proportions. A smell of diesel hangs in the air from the trains transporting concrete up to four miles along the passageway.

Water has flooded the floor after heavy rainfall and we hopscotch about to avoid wet feet but none of the engineers, electricians or fitters appears alarmed. Down here, a leak from above is just another problem to be solved.

John directs me to a section of tunnel where a secondary lining of concrete was recently applied to improve strength and durability so the super sewer meets its 120-year guarantee. “It’s fancy,” he says. “It’s not like the stuff you set your driveway with.”

Each batch must meet rigorous quality control standards or otherwise be discarded.

The shaft connects two main tunnel sections, one leading to Acton and the other to the Nine Elms residential district, the former home of the Battersea Power Station.

Measuring 23ft in diameter – the width of three London buses – in another life, the tunnels’ smooth, snaking curves would make the ultimate skateboard park. Construction of the super sewer is 80 percent complete.

Once finished it will have a storage capacity of 1.6million cubic metres, or 600 Olympic swimming pools. Some 360 cubic metres of concrete are produced every 10-12 hours for the secondary lining, pumped down a fat vertical pipe into the revolving drums of the trains.

Tunnel trials will soon commence

Tunnel trials will soon commence (Image: Jonathan Buckmaster)

There’s also ventilation and odour control to sort before testing trials commence.

Despite London’s continued growth, Roger believes the tunnel will stand the test of time. “It’s been designed by world-class engineering firms and we’ve followed best practice,” he says.

This should be welcome news for the 15 million Thames Water customers who have been paying an extra £19 per year (due to rise to £25) to foot part of the cost.

Of course, the tunnel cannot solve every freak weather event and we can all do our bit by reducing water usage. But the Thames is already far cleaner than in Victorian times, when excrement, industrial waste and abattoir parts were routinely dumped. The Tideway Tunnel will improve things even further.

The original sewers were created after a two-month heatwave in 1858 caused a stench so putrid it was dubbed “The Great Stink”.

Politicians passed legislation granting the Metropolitan Board of Works new powers and chief engineer Bazalgette was tasked with creating a system to protect public health.

Almost two centuries later, something similar is happening again.

The tunnel aims to reduce water usage

The tunnel aims to reduce water usage (Image: Jonathan Buckmaster)

Amid the constant clunking and clanging, it’s hard to imagine this shaft stood in total silence for four weeks at the start of the pandemic. Covid pushed back the opening by several months.

Many of the tunnelling experts previously worked on the Crossrail project and will move to jobs on the HS2 railway afterwards.

Some eight million tonnes of material has had to be brought in and out to build the project and five or six million of that has gone by river, reducing the use of HGVs on London’s roads from 500,000 to 150,000.

Three new acres of “micro parks” along seven locations of the route will also provide a legacy.

Three of these – at King Edward Memorial Park, Tower Hamlets, and Chelsea and Victoria Embankments – will be floodable at high tide so visitors can dip their toes in the Thames.

It’s a nice nod to Sir Joseph, whose sewage system created the Chelsea, Victoria and Albert Embankments so beloved by today’s Londoners.

As my two-hour visit finishes, I’m glad to hand back my oxygen tank to John but I won’t forget that our reliance on the clear, stink-free air outside is only thanks to a hardworking group of people burrowing deep beneath us.



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