Foreword

Like many large infrastructure projects, the story of the Thames Tideway Tunnel goes back a long way before any construction started, with a growing recognition well over 20 years ago that the increasing frequency and volume of raw, untreated sewage spills into the tidal River Thames was unacceptable and that something significant needed to be done about it.London’s sewer system, designed and built by Sir Joseph Bazalgette some 150 years ago, was, and is, working well and doing exactly what it was designed to do to protect the streets of London when the sewers reached capacity – to spill to river by way of the numerous combined sewer overflows (CSOs) that were a fundamental part of the design of the system. Originally, back in the 1870s, this was an infrequent occurrence, but it has progressively increased. This is primarily because the majority of the London sewer network is a combined system that not only receives sewage from buildings but also the rainwater that discharges down the road and street drains throughout much of London. This is not necessarily how you would choose to design a drainage system nowadays, but it is how it was done then. There are three factors that led to the increased frequency and volume of spills to river.This was the backdrop for any new system or upgrade. In a typical year, there could be over 50 CSO spills, with approximately 39 Mm3 of untreated combined sewage entering the tidal Thames.London was thus facing a significant problem and needed a solution as quickly as possible. An unhelpful debate developed around whether a ‘big engineering solution’ was the right thing to do or whether progressive sustainable drainage systems (SuDS) schemes should be considered over a (much) longer period of time. This should never have developed into an either/or ‘binary’ debate. Both approaches should have been pursued, and this polarised argument did not serve London well. An ultimate decision on what to do was delayed, and served, subsequently, to suppress the widespread and prolonged development of SuDS solutions across London. This has still not evolved in any meaningful way, and needs to change if London is to avoid building another tunnel in perhaps five or six decades’ time. The ultimate decision reached was to design and construct the Thames Tideway Tunnel alongside two other components – the Lee Tunnel and the upgrade of numerous sewage treatment works (most significantly Beckton Sewage Treatment Works). Together, this was called the London Tideway Improvement (LTI) scheme. To deal with 39 Mm3 of CSO spills in a typical year, the combined volume of the newly built system was established to be 1.6 Mm3 – it is easy to see that this kind of volume would have been impractical to create through SuDS solutions alone in any meaningful timeframe.With the decision to proceed with the LTI scheme, a phase of value engineering and site selection commenced, which informed the Development Consent Order (HMG, 2014), hand-in-hand with the design development to support procurement of the works. It had been decided that direct delivery by Thames Water was not the best way to proceed. This led to the development of the innovative delivery and financing arrangement that saw the entity subsequently called Bazalgette Tunnel Ltd (trading as Tideway) being established as an independent regulated water company to build, finance and own the project works – all enabled under the newly established Specified Infrastructure Project Regulations (HMG, 2013).A significant engineering challenge in its own right, the task was further complicated by the need to create new land along the river to accommodate construction and operational shafts, and the need to work adjacent to aged sewers, utilities and river walls, and underneath most of London’s iconic river bridges. Imaginative and sometimes innovative approaches were needed, some of which are presented in this special issue of Civil Engineering.Strong support from investors to do the right thing for the environment and for society drove new and interesting approaches to delivering environmental and social value at every opportunity, and these are also discussed in some of the papers in this special issue.The overall project performance has benefitted significantly from the commitment and passion of the people who worked on the project, in many cases for a significant number of years of their careers. Driven by a strong belief in the benefits to be delivered, the career development opportunities that were available and by a positive and enjoyable culture, the significance of this point is not always understood.At the time of writing this foreword, the entire system has been built, integrated into the existing Bazalgette network and is fully up and running, protecting the tidal Thames as originally intended (Figure 1 shows a section of the main tunnel). Further commissioning tests – some of which depend on fairly extreme weather – are ongoing as part of the process of handing routine operations over to Thames Water. To date, over 9 Mm3 of combined sewage has been captured and transferred to Beckton Sewage Treatment Works rather than being spilled into the river.It has been a daunting prospect to collate the key aspects of our learning and, while we could not hope to cover everything that was done on the project, it is hoped that the papers included in this special issue are of interest and use to readers. My thanks go to the authors and to our lead editor/coordinator, Ingrid Lagerberg, for being so diligent and committed to the production of this special issue.