Thames Tideway Scheme


The Thames Tideway Tunnel will be a tunnel running mostly under the tidal section of the River Thames through central London to capture, store and convey almost all the raw sewage and rainwater that currently overflows into the river. Bazalgette Tunnel Limited is the licensed 'Infrastructure Provider' set up to finance, build, maintain and operate the Thames Tideway Tunnel. BTL is a consortium of investors that comprises Allianz, Amber Infrastructure, Dalmore Capital and DIF. From the licence award, BTL trades and is known to the public as 'Tideway'. On 3 November 2015, BTL received its operating licence from Ofwat, ensuring the start of the project.
Started in 2016, construction of the Thames Tideway Tunnel aimed to take seven to eight years with all work completed by 2024. Once constructed, the main tunnel will have an internal diameter of and will run from at Acton in the west of London for over under central London finally reaching at Abbey Mills in the east.
It will connect 34 of the most polluting combined sewer overflows, via transfer tunnels, and was expected to reduce the number of overflow events to a maximum of four per CSO per year at time of commissioning, although increasing gradually due to effects of climate change and population growth. The tunnel will transfer the captured sewage to the Stratford to East Ham part for onward delivery to Beckton Sewage Treatment Works for treatment. The recycled clean water will then be released into the River Thames.
The estimated capital cost – excluding unknown financing costs and ongoing operations and maintenance costs – is £3.8bn to complete, with an additional £1.1bn for preparatory works.

Background

Built between 1859 and 1865, Sir Joseph Bazalgette's original London sewerage system was designed to capture both rainwater runoff and the sewage produced by four million people. As a failsafe, to prevent sewage backing up and flooding people's homes, Bazalgette's system had the ability to overflow into the Thames via 57 combined sewer overflows along the banks of the river.
By 2012, the population of Greater London had grown to an estimated eight million and Thames Water said that the current system lacked the necessary capacity. Bazalgette's original system did not serve all the population, since as London continued to grow in the 19th- and 20th- centuries, outer suburbs were provided with separate sewerage and rainwater infrastructure. Overflows became increasingly common and by the beginning of the 21st-century occurred on average 50 times a year. An estimated total of some, or 39 million tonnes, of storm sewage entered the river in a typical year. These discharges, a mixture of raw sewage and rainwater, needed to be reduced to comply with the EU's Waste Water Treatment Directive and to improve the ecology of the river.

Options assessment

Instigated in 2001, the Thames Tideway Strategic Study, conducted by a group comprising Thames Water, the Environment Agency, DEFRA and the Greater London Authority, was intended to assess the impact of the CSO discharges into the Thames and to identify objectives and propose potential solutions, while keeping costs and benefits in mind.

Outcomes

After four years, the Thames Tideway Strategic Study report was published in 2005, and outlined the following objectives:
  1. To protect the ecology of the Tideway;
  2. To reduce aesthetic pollution due to sewage-derived litter; and
  3. Protect the health of recreational water users

    Potential strategies

Four potential strategies were discussed:
  1. Adoption of source control and sustainable urban drainage;
  2. Separation of foul and surface drainage and local storage;
  3. Screening, storage or treatment at the discharge point to river; and
  4. In-river treatment
After evaluation it was decided that only one strategy, the screening, storage or treatment at the point of discharge, would meet the objectives fully. The remainder were found to be either impractical or insufficient to provide a solution. However, a number of parties questioned the validity of this conclusion, in particular dismissal of SUDs/blue-green infrastructure as a solution. Some groups that opposed the tunnel stated that it is an unsustainable 19th-century solution to a 21st-century problem. They argued that rainwater should instead be captured or slowed down before entering the combined sewers, which would reduce pressure on capacity and take away the need for a tunnel.

Screening, storage and treatment

The three-part solution to implement screening, storage and treatment was collectively known as the London Tideway Improvements.

East Ham to Stratford

The first part was a deep storage and conveyance tunnel from Jenkins Lane, East Ham to Abbey Mills, Stratford. This long tunnel, running up to deep from Abbey Mills to Beckton was to capture, or 16 million tonnes, annually from the single largest polluting CSO in London. Thames Water awarded the estimated £635 million construction contract to the MVB joint venture, made up of Morgan Sindall, VINCI Construction Grands Projets and Bachy Soletanche, in January 2010. The construction of the tunnel began in 2010 and on 28 January 2016 Mayor of London Boris Johnson opened the tunnel for service.

Sewage treatment works modernisation

The second part was the £675 million project to modernise and extend London's five major sewage treatment works to treat a greater volume of sewage, significantly reducing the need for storm discharges to the river:
These upgrade works were intended to improve the standard to which the sewage was treated at each of the works, thus improving the river Thames water quality.

Deep storage and conveyance

The final part was the deep storage and conveyance Thames Tideway Tunnel, which should intercept the outflows from London's most polluting CSOs and direct them to sewage treatment works for processing before they could enter the river.

Thames Tideway Tunnel planning and consultation

Initial design and phase 1 consultation

Following the Thames Tideway Strategic Study, Thames Water consulted with relevant authorities to get feedback from stakeholders who would potentially be affected by the construction of the Thames Tideway Tunnel. Thames Water sought feedback on the proposed tunnel routes and potential locations of construction sites.
Three tunnel routes were considered initially:
  1. River Thames Route – the alignment of this route broadly followed the river from west London to Beckton STW and would cut across the Greenwich Peninsula, reducing the length of the tunnel at a location where there are no CSOs to be intercepted along the river.
  2. Rotherhithe Route – the alignment of this route was similar to the River Thames route, but would have cut across the Rotherhithe Peninsula as well as the Greenwich Peninsula, reducing the length of the main tunnel by approximately but requiring longer connection tunnels from some CSOs.
  3. Abbey Mills Route – this route was different from the River Thames and Rotherhithe routes in that it would connect the Thames Tunnel to the head of the Stratford to East Ham part at the Abbey Mills Pumping Station. This would have followed the same route as the first two options but then deviated from the river toward Abbey Mills. The main tunnel length would be approximately less than the River Thames Route and save approximately £900 million.

    Route and sites selection

A long list of 373 potential sites was created using a desktop survey of the land on either side of the 34 most polluting CSOs. These sites were then further evaluated against more detailed planning, engineering, environmental, property and community considerations resulting in a shortlist of sites.
The three tunnel routes, as well as the shortlist of sites, were then put out for consultation between September 2010 and January 2011. In total 2,389 feedback forms, 480 pieces of correspondence and five petitions were received.
In response to the comments received, changes and improvements to some of the sites, including the potential use of alternative sites and alternative technical solutions, were considered. Based on this a round of interim engagement took place from March to August 2011. Residents around 11 specific sites were sent letters explaining that these sites were being considered as alternative sites, and invited to attend drop-in sessions to pose questions and gain a better understanding of the project. In total ten two-day sessions and one community liaison meeting were held. These were attended by over 800 people. In all 168 comment cards and 147 pieces of site specific correspondence were received and considered.
Based on this first round of consultation and interim engagement it was recommended that, for the project to be as cost-effective as possible and cause the least disruption, while still meeting the requirements of the UWWTD, the preferred scheme for the Thames Tideway Tunnel would need to involve:
The new preferred route and sites were then sent out for a second round of public consultation and feedback.

Phase 2 and targeted consultation

The second phase of consultation was carried out between November 2011 and February 2012 when local authorities, land owners, local businesses and communities were consulted on:
A total of 1,374 feedback forms, 4,636 pieces of correspondence and nine petitions were received.
Following this consultation, and taking into consideration all the feedback received, the proposed route was finalised as the Abbey Mills route and the preferred construction and drive sites were identified. Several sites were also identified as needing further, targeted consultation which resulted in further refinement and improvement of designs at those sites.

Site list and type

To build the Thames Tideway Tunnel, four tunnel boring machines were needed to excavate the main tunnel plus two others for smaller connection tunnels. It also required two types of construction sites: main tunnel sites, where the TBM was either launched or received, and CSO sites, where interception tunnels and a connection culvert were built to connect the existing sewer to the new tunnel.
Construction of the shafts at the CSO sites, to transfer flows from the existing sewer to the tunnel, would vary depending on the depth, the amount of flow they need to carry and the geology. The shaft would be a concrete cylinder with an internal diameter of and deep. Ventilation structures at CSO sites to allow air in and out of the shaft were also required. Construction at these sites was expected to take between and years and once complete each site would be landscaped.
At the main drive sites, four main activities took place: shaft construction, tunnelling preparations, TBM assembly and lowering into the shaft, and then driving the TBM to excavate the main tunnel.
As the TBM moved forward precast concrete segments were brought in and fixed together to create the tunnel wall. Excavated material would be transported out the tunnel via a conveyor belt and processed before being taken off site. In order to minimise disruption, Thames Water committed to use the river as much as possible to transport materials both in and out of the construction sites. At the main tunnelling sites, work was expected to occur 24 hours a day.
In 2017 the public voted on a short-list of 17 to name the six TBMs. They were named after inspirational women with a connection to the area where each individual machine started its journey. One began tunnelling from Fulham in 2018 and was named after Rachel Parsons, an engineer and advocate for women's employment rights, who set up the first women-only engineering company in Fulham. The others were cryobiologist Audrey ‘Ursula’ Smith and suffragist Millicent Fawcett for the Central area and suffragist Charlotte Despard for the Frogmore Connection Tunnel from Wandsworth to Fulham. The TBM that would tunnel the east section from Bermondsey was named after doctor Selina Fox who set up Bermondsey Medical Mission for Southwark's poor and disadvantaged residents. The machine for the Greenwich Connection Tunnel was named after Annie Scott Dill Russell, the first female scientist to work at the Greenwich Observatory.

Planning application

In October 2012, the deadline for the Thames Tideway Tunnels' Section 48 closed. This lasted 12 weeks and was the last opportunity for the public to have their say on the updated proposal.
The Application for Development Consent – a detailed plan for construction of the Thames Tideway Tunnel – was delivered to the Planning Inspectorate on 28 February 2013. The Inspectorate then had 28 days to decide whether the application was valid and whether the consultation undertaken was adequate. On 27 March 2013, it was confirmed that the application was valid and that Thames Water's consultation for the project had been adequate. All the application documents were made available in their own section of the Planning Inspectorate's National Infrastructure website. Thames Water also made the documents available for scrutiny at six public locations along the tunnel's proposed route, three either side of the river.
On 3 June 2013, it was announced that the Secretary of State for Communities and Local Government had appointed five inspectors as the examining authority to consider any matters arising. As part of this process, interested parties were able to make representations.
A preliminary meeting, open to those who had registered an interest, began on 12 September 2013 at the Barbican Centre. Chaired by the Planning Inspectorate, this determined how the examination would be carried out, including consideration of more detailed hearings on site-specific matters, as well as project-wide issues. Once the Inspectorate concluded its examination of the application, a recommendation on whether or not to grant approval would be submitted to Government ministers to make the final decision.

Planning acceptance

On 12 September 2014, the UK Government approved the plans, overriding some of the findings of the Planning Inspectorate. The decision gave rise to at least three Judicial Reviews.

Funding and delivery

The budget for the scheme steadily increased since it was first estimated. For example, the budget in 2004 was estimated at £1.7bn, which included the East Ham to Stratford part and sewage treatment works upgrade costs. In the words of the Consumer Council for Water in 2011:
"The estimated cost of the project has escalated, from £1.7bn in 2004 to £2.2bn in 2007 to £3.6bn now for the shorter Thames Tunnel as far as Abbey Mills, plus some £1bn for the Lee Tunnel and upgrade of works at Beckton. The total costs of all the Tideway schemes have therefore increased from £1.7bn six years ago to £4.6bn today. There is no guarantee that the current estimate will not be subject to further escalation."

Less than a year later, in November 2011, a further £500 million was added to the estimate.
Following detailed analysis it was decided that the best means to deliver the project would be through a regulated infrastructure provider as this would maximise value for money. The IP, originally to be formed through a competitive process starting in the spring of 2013, would hold its own license from the industry regulator, Ofwat, and would build, manage and maintain the tunnel.
In January 2013, it was announced that procurement of the IP was to be delayed because Thames Water needed more time to define the funding model to secure financial assurances from the government. The subject of taxpayer support for the construction of a tunnel was a source of controversy, with opponents arguing that the government should not bear risks associated with the project. In a letter to the Financial Times in November 2012, Sir Ian Byatt and politician Simon Hughes MP stated:
If Thames is unwilling to make a rights issue, the owners, Macquarie, should be expected to return funds to the utility. If they do not, Thames should go into special administration and another company or financier allowed to take over its activities.

However, procurement for main contractors for up to three packages of work valued at around £500m each started in the summer of 2013. On 29 July, Thames Water announced that a contract notice for work on the tunnel had been published in the Official Journal of the European Union. Following prequalification questionnaires, Thames Water invited shortlisted contractors to tender between November 2013 and April 2014.
The successful contractors for the three main tunnelling contracts were announced in February 2015:
In August 2015, the independent investors to finance and deliver the scheme were confirmed. Bazalgette Tunnel Limited, a new special-purpose company appointed to take the project forward, received its licence from Ofwat as a new regulated utilities business, separate from Thames Water. The special-purpose company is backed by pension funds and other long-term investors represented by Allianz, Amber Infrastructure Group, Dalmore Capital and DIF.

Planned timeline

  • 2014: Planning decisions and approval
  • 2015: Main works and financing contracts awarded
  • 2016: Primary work completed; Main works preliminary construction begins
  • 2018: Tunnelling begins
  • 2019: Secondary lining begins
  • 2022: Tunnelling ends
  • 2024: All works completed.

    Controversy

Since the initial proposal, questions were raised about the scheme's cost, the location of construction sites, the project's duration, the disruption it caused, and whether a tunnel was the correct solution – or even necessary at all – for London and Thames Water customers.
Cost
The £4.2bn cost of the Thames Tideway Tunnel project was to be funded entirely by Thames Water customers. This has angered some customers who believe the company has benefited from tax breaks sanctioned by industry regulator, Ofwat, when it was allowed to add debt to its balance sheet, reducing its tax payments while allowing its shareholders to receive dividends – money some customers feel should have been spent on the Thames Tideway Tunnel. Thames Water maintained it has done nothing unusual by raising debts to reduce tax bills and that this was following conventional practice. It said the money raised was used for essential maintenance and upgrade works, although some have asked questions about how Thames Water paid so little corporation tax at the same time as distributing dividends to its shareholders.
Disruption
Some people who live alongside proposed sites were concerned about the noise, disruption and potential loss of public space resulting from construction. To address this Thames Water put together a Code of Construction Practice which outlined both site-specific and project-wide requirements and measures that it said would minimise the impacts of the construction and ensure that best practice standards and requirements were implemented across all sites and contracts. The Code also covered transport, noise and vibration mitigation, air quality and water resources, land quality, waste management and resource use, ecology and conservation and historic environment. In the report that concluded its inspection of these documents, the Planning Inspectorate found that Thames Water had "underestimated of impacts on those that have been identified as having a significant effect and underestimated the number of receptors experiencing a significant effect" and concluded "We do not consider that proposals meet the first aim of the NPS test to avoid significant adverse impacts on health and quality of life from noise".
The need for a tunnel
Some people maintained that a sustainable urban drainage solution or green infrastructure would remove the need for the tunnel. They argue that replacing paved, impermeable surfaces in London with permeable options and implementing green roofs, swales and water butts would promote the infiltration of rain-water, preventing it from reaching the combined sewer system, thus reducing peak flows and limiting the number of CSO overflows. Opponents of the tunnel felt that these measures would provide the level of control required and be cheaper than the proposed tunnel. They also argued that green infrastructure would have further benefits for London in addition to addressing the rainwater overflow problem, such as:
  1. Increased resilience to drought and floods,
  2. Reduction in urban air pollution,
  3. Climate change mitigation – contrasted to the tunnel's significant carbon footprint,
  4. Enjoyment, aesthetics and health benefits of green spaces and nature,
  5. Reduced urban heat island effects with an associated reduction in cooling load and carbon emissions,
  6. Improved urban biodiversity.
  7. Earlier avoidance of EU fines for not meeting water standards than under the scheme.
The earliest customers’ bills would be affected was 2014–15, with charges rising gradually after that. The project was estimated to add up to £70 to £80 to average annual wastewater bills from around 2019. However, these figures were subsequently revised downwards. In August 2015, the impact was expected to be around £20 to £25 per year by the mid-2020s.

Archaeological discoveries

Much like the Crossrail and High Speed 2 projects that were going on at the same time as Tideway, the development gave archaeologists the chance to uncover the hidden secrets of London's past. In late 2018, a 500-year old skeleton of a man found lying face down in the mud on the banks of the River Thames at the Chamber's Wharf site in Bermondsey was discovered. The skeleton was still wearing his knee-high leather boots, suggesting that he may have been a fisherman or mudlark who died an accidental death.
A World War II bomb was also discovered by Tideway engineers in Chelsea in December 2019.