WET News

AUGUST 2014 WET NEWS 9 CV A Chartered Civil Engineer, Stride has worked for Thames Water for 40 years this Septem- ber, spending his whole career in either engineer- ing or operations. He was previously head of capital delivery and prior to that was project director in various areas of the engineering business. "I've had good operational experience in London of operating sewage systems which is good when you're building a project that is basically to extend the sewage system. "I've didn't have experience of building projects quite this big until I was responsible for the Lee Tunnel and the Thames Tunnel." I n just over a month's time Thames Water will know if its planning application to build the £4.2B Thames Tideway Tunnel (TTT) has been successful. Phil Stride, head of the Thames Tideway Tunnel, is confident it will go through. "We're confident in our application and whilst we're considering all possibilities we're planning on the basis that we'll get a development consent order." The Tideway Tunnel is needed to tackle the millions of tonnes of raw sewage that discharges into the tidal River Thames every year. When completed in 2023, it will act as an interception, storage and transfer tunnel. The tunnel's proposed route follows the Thames to Limehouse and then goes north-east to Abbey Mills Pumping Station near Stratford. From there it will connect to the Lee Tunnel, which will transfer the sewage to Beckton STW. Thames Water will be responsible for £1.4B of the cost of the project and the remaining £2.8B will be down to the independent infrastructure provider (IP). CH2M Hill has been the programme manager on the project, having been appointed in 2008. Fundamental The tunnel is a one in a 150-year project in the UK water industry, says Stride. "There hasn't been a project of this scale since the 1860s when [Joseph] Bazalgette built his inceptor sewers in London, which at the time was the largest civil engineering project in the UK in the nineteenth century. "It's a fantastic project and a privilege to work on it." He says that when Bazalgette built his sewers there were two million people in London but he had the foresight to design the network to be large enough to deal with four million. "There are now eight million people so it is a fundamental piece of infrastructure that's needed for London, and something that will provide a tremendous legacy for many generations to come. It's a very special project by any standard." The tunnel has attracted its share of detractors but Stride firmly believes it is the right solution to take London's sewage needs into the next century. "Last year, 55 million tonnes of sewage was discharged into the tidal Thames. That is a massive volume. "It's a scale issue. If we tackled half of the rainwater that went into the sewers we'd need an area 40 times the size of Hyde Park to take the flow to. That's only half of it, and as the UK we would still fail to comply with the Urban Wastewater Treatment Directive as well. "We estimate that a SUDs project to meaningfully reduce the amount of rainwater going into the sewers would cost something like £13B – and you would end up virtually digging up the vast majority of London streets. The scale of disruption would be immense." Stride continues: "You've got 1.6Mm 3 of sewage in that tunnel, and what is difficult to articulate to people sometimes is how that volume could be catered with if you had sustainable drainage systems. If you had water butts, green roofs, swales even green areas where you stored it until it evaporated or soaked away. It's dealing with that volume." Densely populated The Tideway Tunnel is certainly proving a challenge. "It's a large piece of infrastructure being constructed through the middle of one of the most densely populated capital cities so it has been a challenge working out how to construct 25km of tunnel from one end of London to the other." The project has been split into three packages, West, Central and East, and there will be 24 sites spread across the three with up to 9,000 jobs created. Stride says selecting the sites was one of the first challenges. "Had we done this 20-30 years ago, the availability of sites we had to choose from would have been greater. One of our key sites selection methodology caveats was that we wouldn't knock down residential development." Then there has been the type of tunnel boring machine used to cater for the varying geologies as well as the depth and pressure involved. "In the west we will tunnel through clay; the central section will go through mixed sands and gravels; and in the eastern section we will be tunnelling through chalk." Another challenge is going to be dealing with outfall drops into the main tunnel. Stride explains: "Take the Fleet sewer [at Blackfriars Bridge], for instance. The design flow for the future is to drop to 50t/s down into the main tunnel which is 50m deep. We've got to manage the amount of energy that would be involved in that, and how we can dissipate the energy. We've also got to make sure we don't entrain air into the tunnel. "That would be very bad." n Phil Stride Head of the Thames Tideway Tunnel INTERVIEW WhaT you didN'T kNoW! It's not good for my image but I like... Looking after my garden I drive... I'm a keen user of the train (we work in Paddington!) I'm currently reading... The brilliant Lustrum, by Robert Harris My greatest weakness is... Saying no to my daughters The album currently in my car CD player is... Jake Bugg "There hasn't been a project of this scale since the 1860s when Bazalgette built his interceptor sewers in London, which at the time was the largest civil engineering project in the UK..."

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