The first episode follows the creation of the first stretch of the supersewer in east London. Lead engineer Emmanuel Costes has to build a massive 80-metre deep shaft that connects to the supersewer and make it watertight using a specialist technique called 'slipform'. It is a risky approach as it involves pouring concrete constantly for 15 days - and delays could spell financial disaster. The programme follows Steve Perry and his team at the treatment works in Beckton as they attempt to install the biggest pumps ever used in Britain to deal with sewage. The pumps are critical - with so much more sewage due to head to Beckton via the new supersewer, each one has to be capable of pumping three cubic metres of sewage per second. If they aren't installed correctly, millions of tonnes of the capital's waste will be stuck underground. Originally built when the population was two million, the Victorian sewers now service nearly nine million Londoners. The episode shows how this growing population means the existing sewers need constant maintenance in order to work at full capacity. With huge residential developments being built across the city, a group of sewer technicians (aka flushers) are sent in to survey the old sewers and plan for new connections. The programme follows Emmanuel, Steve and the team, who are up against the clock to finish the first section of the new supersewer so that it can be put to work in time for the opening ceremony.
In this second episode, construction begins in the heart of London. Two key connection shafts along the Thames are to be dug to enable the super-sewer to be built. In Battersea, a challenging construction technique called 'diaphragm-walling' is employed to build a massive 90-metre-deep shaft. But these are the deepest tunnels ever dug in London, and with challenging rocks that haven't been disturbed for 52 million years, the digger struggles to cut through the ground. At Tower Bridge, engineers need to build a cofferdam structure out into the Thames to make enough space for the second shaft. Reclaiming 8,000 square metres of land in central London is a noisy operation, and not all of the neighbours are happy. Finally, with tunnelling about to begin, engineers need to solve the problem of where to put up to 1.5 million tonnes of earth and rubble that excavation will create. They plan to take the earth by barges out of London to Tilbury, but the current dock is too small to deal with the vast amount of dirt that will be excavated. It is decided to build a new dock by positioning a 70-tonne bridge on steel pillars and installing a massive platform.
In this third and final episode of the series, tunnelling in central London finally begins. To complete the 16-mile main section of the super sewer, four bespoke tunnelling machines have been designed and work is underway to prepare for their launch. In Battersea, one of the strategically most important sites on the project, the team must assemble the £15m tunnel boring machines on site. The 100-metre-long, 9-metre-diameter machines have been stripped down into component parts and sent from the manufacturer in France. Now the team has just three months to put together the 900-tonne jigsaws, before lowering them 60 metres into the ground, to begin tunnelling in earnest. Ahead of the machines setting off, the opening section of the tunnel in Battersea has to be burrowed by excavators and reinforced with spray concrete lining to prevent it collapsing. The team are on a tight two-month schedule, but when their tunnellers hit the 52 million-year-old compressed rock of the Upper Shelley Beds, progress is in peril. On the Thames, there's a much-needed boost for the tug and barge industry, as super sewer project managers commit to moving 90 per cent of waste material from the tunnels by river - and that means opportunities for ambitious crew who are looking to make a step up. But the mammoth engineering effort of the super sewer team isn't good news for everyone on the Thames. Bright yellow amphibious Duck Tours vehicles that take tourists through the city centre are forced off the river, as engineers need to take over the river bank they use to launch.
