Episode 4: Inside London's Super Sewer

0:02The system does not have enough capacity when it rains because it's a combined system. So when it rains, the rainfall combines with the sewage and we have to pump that and treat that. The original system that Sir Joseph Bazalgette designed was designed for four million population. We're now over double that. So yeah, there is a capacity infrastructure problem.

0:26Lucy Tobin: That was Dina Gillespie speaking to us in the last episode inside Abbey Mills Pumping Station in East London. In this episode, we discuss one response to the growing capacity problem. For years, London has been building the Tideway Tunnel, one of the largest upgrades to its sewer system since the Baseljet era. A 16-mile tunnel beneath the Thames, designed to stop millions of tonnes of sewage spilling into the river. It's now operational. But as climate change brings more frequent and intense rainfall, what are the limits of the tunnel built beneath London? This is Thames Unfiltered from The Standard, in association with Thames Water.

1:16Lucy Tobin: I'm your host, Lucy Tobin, business journalist and author. Across the series, we're asking how healthy the Thames really is, who shapes it, who's responsible for it, and what needs to happen to safeguard its future. In this episode, we're asking what happens when London's hidden wastewater system is pushed beyond its limits.

1:52Lucy Tobin: To understand what the Tideway Tunnel can do, we need to go back to 2011, when London's sewers first began to be upgraded. Hey, George. Keep bringing it down, Melbourne. Martin puts himself on the front line. Lizzie's close enough to touch, but it's the only way to guide her past the scaffolding. That's a clip from the TV series Dirty Great Machines when a Channel 5 film crew shadowed Thameswater's engineers at work. How's she looking? She's still clear. How much can we slow to your right? OK, George, just slow it right, mate, because it's nice and easy, mate. They followed the lowering of a gigantic tunnel boring machine called Busy Lizzie down a 75 metre deep shaft at Becton Sewage Works.

2:49Lucy Tobin: Lizzie was deployed to dig the Lee Tunnel, 4.3 miles connecting Becton with Abbey Mill's pumping station. The Lee Tunnel was the first major section of a wider upgrade to London's network, one that would eventually include the Tideway Tunnel.

3:09It's taken four hours, but finally Lizzie's home and dry. Now work can begin on London's deepest ever tunnel.

3:23Lucy Tobin: That was a risky and expensive project fraught with danger. At the time, as little as two millimetres of rainfall would release sewage into the Thames. There were 36 sewage pipes lining the river known as combined sewage overflows Something needed to be done to stem the sewage and modernise London's Victorian sewage network And after years and years of consultation, political negotiations, legal reviews and fundraising from private investors A decision was made A massive 7.2 metre wide tunnel would be dug beneath the riverbed Diverting the poo away from the Thames Well that was the plan Such a tunnel had never been built in Britain before Let alone in the middle of its thriving, busy capital city Avoiding London's gridlocked roads The Thames would become the highway The way in for construction materials and another six tunnel boring machines.

4:30Lucy Tobin: And the way out for thousands of tonnes of excavated soil. Chris Livett, 7th generation waterman, explains more.

4:46My involvement with Tideway Tunnel really starts from conception. I was a consultant to them in design of jetties, moorings, types of barges, locations for disposal, passage planning, training. There was a cultural shift for the people that worked on the project.

5:03Lucy Tobin: Chris's firm built eight huge new barges with names like Churchill, Pegasus and Valiant, capable of carrying over 1 ,000 tonnes of material. To tug these barges safely required a new generation of highly trained watermen. There was a huge training programme we put everyone through. Tideway sponsored a simulator for tug captains, which was the first ever in England, I think, local tug captains. And we helped Thames, well, Tideway, Tidewall and Thames Water raise the bar, raise the standards of transportation afloat. Once the Lee Tunnel was completed in 2016, work began on the main 16-mile section, from Acton in West London to Abbey Mills.

5:48Lucy Tobin: Like most Londoners during this period, I rode the Tube to work every day and had no idea that something so consequential was happening. Chris was one of more than 25 ,000 people working on one of the most ambitious infrastructure projects London had seen in generations. We transported 1.25 million tonnes of spoil downriver for land reclamation and we brought in approximately 600 ,000 tonnes of tunnel segments to build the tunnel itself. We also brought in cranes and offices, slipways we built for it up at Putney. And we worked all through Covid. We were one of the few people working during the Covid period.

6:2624 hours a day, seven days a week, on time, on budget, no accidents. And to shift that amount of tonnage through London without anybody blinking was quite an achievement, I think.

6:39Lucy Tobin: Sections of the Tideway Tunnel opened in August 2024 and it was fully operational six months later It cost£4.6 billion which was£1.1 billion more than planned although disruption from the pandemic was one factor in that increase The project has attracted international attention both for its scale and its safety record But for Tim Davies, Thames Water's head of waste operations in North London, there's really only one stat that he's interested in. The Tideway Tunnel is having such a massive impact on reducing those intense rainfall spills to the river. We have prevented 20 million tonnes of wastewater from going into the Thames.

7:25And just to try to put that in some sort of way for people to understand, the volume of the Tideway Tunnel is about 600 Olympic swimming pools. So it's about 1.5 million tonnes. And the total volume that we've prevented from going into the Thames since the tunnel was put into service is 20 million tonnes, which is the equivalent of 8 ,000 Olympic swimming pools. So as a consequence of that not going into the Thames, that is really helping to improve the water quality in the Thames. I also love the fact that cormorants, this is my favourite fact, In fact, cormorants, which you see all the time on the river, eat a quarter of a tonne of fish every year.

8:08So whenever I see a cormorant, I think, well, there must be a lot of fish in this River Thames here if they eat a quarter of a tonne a year. So the Tideway Tunnel is having a big, positive ecological impact on the Thames.

8:22Lucy Tobin: The Tideway Tunnel is not only making the river cleaner, it's also reshaping London. Public spaces have been constructed on top of the various access tunnels along its route. Sir Peter Bazalgette, great-grandson of Sir Joseph, is taken with the Thames' new look. They've created seven new public gardens along the river. I've opened one of them and been to the opening of about three others. I went to the opening of the one by Chelsea Hospital, which again Princess Anne opened. And it was rather good to see the royal family coming along to applaud and celebrate public works. In the same way that the Victoria Embankment was created to hide Sir Joseph's first trunk sewer, these seven new gardens are a showy addition to the Thames' waterfront, complete with public art, herbaceous borders and curved stone.

9:15Lucy Tobin: They might be the prettiest giant manhole covers around. Perhaps the most elaborate is called Basiljet Embankment, and that's the one by Blackfriars Bridge now open. And if you stand in the middle of it at the right place, you can just get a wonderful view of St Paul's. What could be lovelier than eating your Pret sandwich looking at St Paul's at lunchtime? For Londoners, which is one of the great cities of the world, these seven new gardens celebrate a river that we used to ignore. We didn't really take the river seriously. We didn't regard it as a great piece of beauty, an environmental asset.

9:51It means that the river is a great enhancement now. And if you think of that added to the fact that the river is going to be so much cleaner going forward, and I guarantee you, I predict with confidence that you will see many, many more fishermen up and down the river, whiling away their day, catching a really wonderful array of fish going forward in the future.

10:15Lucy Tobin: The main access point to the Tideway Tunnel is via a 51-metre drop located at the Baseljet embankment So as Londoners stroll along the riverbank beneath their very feet, sewage is being captured and diverted sewage that would otherwise be spilling into the Thames But while the Tideway alleviates poo pollution in the tidal Thames it's no fix for London's flooding problem

10:48Now I should just clarify that there are some overflows that are not connected to the tunnel so in heavy rain those discharge points can still discharge.

11:00Lucy Tobin: Tim Davies of Thames Water again. While the tunnel is not designed as a flood alleviation scheme it should give some relief. It's reducing the environmental impact of storm overflows to the tidal Thames by 95%, but it hasn't intercepted every single storm overflow. So in terms of what it hasn't done, there are still about 10 connection points which are not connected to the tunnel. Flash floods are defined as more than 30 millimetres of rainfall in an hour. The Met Office predict that by 2070, they will happen twice as often as they did in 1990. At the same time, London's built environment has become even more ill-equipped to handle these intense downpours.

11:45When you stand in some parts of London and you look on the ground and you think, if we have a massive rainstorm, where does the rain go? And everything has been paved over. It's been measured that London is one of the least, what they call, spongy cities. so the ability of the ground in central London to absorb water is one of the poorest cities in the world at doing that.

12:12Lucy Tobin: Since the start of the 21st century, central London has lost green spaces equivalent to the area of two Hyde parks. We've paved over our front gardens to allow us to charge our electric cars and put patios and decking in back gardens to make the most of the summer. The growth of high-rise developments is another factor in what professionals like Alex Nixon, head of catchment management for Thames Water, calls urban creep.

12:43Urban creep causes rainwater to run more quickly off those surfaces into our sewers and is a very pressing challenge to manage. Our drainage systems are not designed for the climate we will experience in the future. So it is important that we take the strain off our drains by re-greening London.

13:04Lucy Tobin: Thames Water and other utilities reckon one solution is something called Sustainable Urban Drainage Systems, or SUDs. These slow down the water going into the sewers during flash flooding or divert it entirely. We were co-founded something called the Flood Ready London Partnership. So this brings together all the London local authorities, the Greater London Authority, Transport for London and the Environment Agency together. We looked at what were the key problems that were driving this flooding and we identified that it was largely due to this large increase in impermeability. Bigger, more expensive SUDS projects are taking place across London.

13:47So you've got two options, slow the flow into the sewer or take the rain out. We have an office near Hammersmith and there's a road that leads to our office called Chancellor's Road. and the local authority Hammersmith and Fulham we're working very closely with them to work together on how to resolve these flooding problems and Hammersmith and Fulham took all of the road drains and it piped them into the local park so it dug a big hole in the park and put what's called a soak away which is a gravel bed that allows rain water to soak into the ground so it took all of the rain out of that sewer along Chancellor's Road and connected a pipe into the park so that that rain now gravitates down into the ground rather than causing our sewer to be overwhelmed.

14:36Lucy Tobin: Architects now have to implement suds into their designs for new buildings. Existing houses, flats and offices however are reliant on the effectiveness of community planning for flooding. They've been very helpful in helping us identify things like flood flow routes. Where does the water run from? So we can use that information in our flood models. And then the community plan then starts to look at, well, what can we do to protect ourselves? So some of it is just very simple stuff. You know, can as a community, can we come out and maybe clear the leaves off the drainage gullies in autumn? Also, what these communities have been very helpful in doing is identifying locations for installing things like rain gardens or street trees that can absorb that rainwater and take the strain off our drains.

15:24So, you know, picking one community in Camden, the South Hampstead Flood Action Group, they've been very successful in identifying locations within their community for these rain gardens and have succeeded in getting funding for four projects in their area. and these cumulatively build, you know, as we deliver more of these, they gradually help us reduce the amount of rainwater getting into our drains. And what they also are is very powerful advocates because you may not be surprised that sometimes our customers don't want to hear what Thames has to say, but if they hear it from a community that's been affected, then people may be more minded not to pave over their front gardens.

16:05So they become very powerful advocates of the necessary change.

16:13Lucy Tobin: There is no single fix. Instead, London is looking at lots of smaller interventions that together can slow the water down. Some are big schemes organised by councils, others are small changes on individual streets. But they are all trying to do the same thing, stop rainwater from overwhelming the sewer network all at the same time. So it's the creation of more parks, it's the creation of soak-aways, it's the creation of permeable paving where we would lay roads that allow the rain to soak through it. Tanks on the side of buildings that capture rain and allow it to drain slowly into the system rather than it surging into the system.

16:57Lucy Tobin: Ultimately, thinking about what we individually flush down the toilet and drain down the sink can also make a big difference. blockages in the sewer are public enemy number one, if you like. We're removing about 75 ,000 blockages a year from our sewer system, which is costing our customers an absolute fortune. When you pour fat down a sink, that fat congeals into a really hard concrete-like substance in the sewer and can produce a fatberg. And those fatbergs can sometimes be absolutely massive. You know, we've got sewers that are one metre in diameter that might have, you know, potentially 100, 200 metre long fatberg that we have to send people in to chisel out by hand.

17:42So please, if there was one takeaway from this podcast, it would be to beg our customers. I'll go down one knee if you want to say, please, please, please. Whenever you're in the bathroom, the only thing that goes down the toilet is toilet paper. kitchen roll tissues wet wipes sanitary items all of that belongs in the bin and when you're at your kitchen sink please don't flush the milk down please don't flush the yogurt down or the gravy from the sunday roast all of that has to go in the bin because you will be helping to protect your river and you'll be helping to keep your water bills down thinking twice about what you

18:22Lucy Tobin: flush down the loo will not replace the bigger work. Investment, planning, regulation, drainage, parks, roads and the way London prepares for heavier rain. But it is a reminder that this system is connected to everyday life. What we build, what we pave, what we flush, what we pour, it all ends up somewhere. The Tideway Tunnel has changed what happens beneath the Thames, but London's next challenge is above ground. As climate change brings more frequent and intense rainfall, the question now is whether the city can adapt quickly enough.

19:04Lucy Tobin: This is Thames Unfiltered by The Standard, in association with Thames Water. Next time on Thames Unfiltered, we'll hear from an MP who has caught up in a sewage flood. and I'm asking Catherine Ross, a director at Thames Water, the questions that customers want answered. Although we are called Thames Water and Thames Water is very important for what we do, we're not the only contributor to the health of the River Thames.

19:42Lucy Tobin: This podcast was produced by The Standard and Message Heard in association with Thames Water with all content created under The Standard's editorial control. I'm your host, Lucy Tobin. From The Standard, Tori Frost is our executive producer and Vanessa Cutt is our senior project manager. From Message Heard, Mark Kendrick is our senior producer, Will Aspinall is our producer, Martha Tipper is our assistant producer. Lizzie Andrews and Alan Lear are our audio engineers. And James Cox is our production coordinator.