How the Thames Tideway Tunnel is cleaning up London

After eight years of construction, London’s super sewer is now  up and running. Last month, Tideway (the company set up to deliver the project) announced that the first steps had been taken to ensure that the harmful effects of sewage pollution in the River Thames through central London would be consigned to history.

The problem Tideway was set up to solve dates back to the mid 1800s, to an event flippantly described in the history books as the Great Stink. In reality, an unrelenting concoction of human and animal excreta, industrial waste and the runoff from abattoirs had poisoned the Thames. A foul-smelling miasma rose from the river. London’s air was tainted with the stench of putrid decay. Denizens pinched their noses and clutched hankies close to their faces. Politicians were eventually forced to act.

The not-yet-knighted Joseph Bazalgette, then chief engineer for London’s Metropolitan Board of Works, was tasked with solving the problem. He designed and oversaw the construction of a vast, pan-London infrastructure project that not only cleaned up London’s great river, but saved countless lives by limiting the spread of cholera. More than 300m bricks were used in the construction of an immense network of drains and sewers. Foul flows were diverted away from the city centre. The river recovered. Bazalgette built London’s Victorian sewer system to last – doubling the required capacity to cope with a population twice the size. Today, however, London’s population has more than doubled again.

Added to the increase in people, modern Londoners are using far more water than their Victorian counterparts. Meanwhile, successive generations have concreted over thousands of acres of natural soakage, paying little attention to the permeability of our city. And therein lies the problem. Where does all that rainwater go? Straight into the sewers, which quickly fill to capacity. In order that our streets and homes don’t flood with sewage, valves up and down the banks of the Thames creak open to spill the euphemistically named “storm flows” directly into the river. A century ago, this was a relatively rare occurrence. In recent times, however, an average year saw around 40m tonnes of sewage spill, untreated, into the Thames. Until now.

The Tideway solution is a simple one: intercept sewage spills before they hit the river and divert them away for treatment. In practice, the project has involved complex civil engineering work at 24 sites, the construction of a 25km-long, 7.2m-wide tunnel (London’s deepest), the work of almost 25,000 people and more than 40 million working hours. Connecting this new infrastructure to the existing Victorian system has been a meticulous operation, and we have faced many a challenge along the way. Yes, we’ve had the usual slew of “typical” problems that face all big infrastructure projects: unexpected ground conditions; navigating the interface between the new and the old; and working in the heart of one of the world’s global cities.

But we’ve also had to deal with the wholly untypical challenge of delivering a multi-billion-pound infrastructure project through a once-in-a-century global pandemic. Despite all this, the super sewer is now on. At 21 points along the banks of the Thames, we’ve built up to the spill points and installed new infrastructure that is intercepting spills and channelling them down into the new tunnel which transports the flows to a treatment plant in east London. And at the time of writing we are making good progress on the necessary connections, with the project on course for full completion next year.

The super sewer’s protection of the River Thames has begun – an essential step in responding to one of the greatest environmental issues of our time. With this milestone achieved, London now has the opportunity to change. We must be smarter about how we treat rainwater. Simply channelling rain into the same pipes and tunnels as our foul water is not a sustainable solution, and unless we are prepared to think and act differently about the way we grow our cities, the opportunity could be lost. The challenge for industry leaders and policy makers is to look beyond the next project, beyond the next decade – just like Bazalgette before us. The “spongification” of London is an essential part of transforming it into a sustainable, thriving city – and, with enough imagination and strategic thinking, I believe it is achievable.

The Tideway project is unique in many ways. Foremost among these is its funding model. Private capital funded the construction. And the cost of securing that capital was lowered thanks to government-backed guarantees (which have never been called upon). Having the state as the guarantor of last resort has been a key feature of the model, that has, crucially, kept the cost to the bill-payers low. This year, the cost is £26 per household – which remains within the cost range promised back in 2015, and well below early estimates of £70-£80. And at a time when investment in critical infrastructure is an issue at the top of the agenda, it is right that the Tideway model is being considered elsewhere.

We hope that part of our legacy is to raise the bar for the industry in meaningful ways, including in health, safety and wellbeing, and in setting new benchmarks for socially conscious project delivery. It is now up to others to build on that legacy. Infrastructure must be driven by clear objectives. But it must also be cognisant of its wider context, of its role beyond simply “upgrading” or “expanding”. We must consider how our infrastructure works to create the environments, communities, and cities in which we want to live for generations to come.