Thames Tideway Scheme
|Thames Tideway Tunnel|
|Type||Urban wastewater infrastructure|
|Construction Period||2015 - 2023|
|Tunnel length||25 km (16 mi)|
|No. Of CSOs intercepted||34|
|Depth||30 m (98 ft) – 70 m (230 ft)|
|Tunnel diameter||7.2 m (24 ft)|
|Cost of construction||£4.2 billion (2012 capital cost est.)|
The Thames Tideway scheme is a proposed 25 km (16 mi) tunnel running mostly under the River Thames through central London, intended to provide storage and conveyance of combined raw sewage and rainwater discharges that currently overflow into the river.
The proposed solution favoured by Thames Water involves construction of a tunnel (the Thames Tideway Tunnel) running from Acton in the west of London through to Abbey Mills in the east, controlling 34 of the most polluting combined sewer overflows (CSOs) via transfer tunnels along the way or system modifications. The captured sewage would then be transferred to Beckton Sewage Treatment Works (currently being upgraded to increase capacity) via the Lee Tunnel (already under construction) for treatment before being released. The main tunnel will be approximately 25 km (16 mi) long and have an internal diameter of 7.2 m (24 ft). It will run through the centre of London, mostly under the River Thames, at a depth of 30 m (98 ft) in the west through to 70 m (230 ft) in the east.
Once constructed the system is expected to reduce the number of overflow events to a maximum of four per CSO per year at time of commissioning, increasing gradually due to effects of climate change and population growth.
Starting in 2015, construction of the Thames Tideway Tunnel would take eight to nine years. Its current planned target completion date is 2023.
The current estimate of its capital cost - excluding unknown financing costs and ongoing operations and maintenance costs - is £4.2 billion in 2012 prices. The budget for the scheme has steadily increased since it was first put forward - for example, the stated budget in 2004 was estimated at £1.7bn, which included the Lee Tunnel and sewage treatment works upgrade costs. In the words of the Consumer Council for Water:
"The estimated cost of the project has escalated, from £1.7bn in 2004 (including Lee Tunnel and sewage treatment works (STW) costs) to £2.2bn in 2007 (also including Lee Tunnel and STW costs) 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 (all costs at relevant year prices). There is no guarantee that the current estimate will not be subject to further escalation."
Less than a year after this writing, a further £500m was added to the estimate.
- 1 Background
- 2 Options assessment
- 3 Thames Tideway Tunnel planning and consultation
- 4 Funding and delivery
- 5 Controversy
- 6 References
Built between 1859 and 1865, Sir Joseph Bazalgette's original London sewerage system was designed to capture both rainwater run-off and the sewage produced by four million people. As a fail-safe, to prevent sewage backing up and flooding people's homes, Bazalgette's system has the ability to overflow into the River Thames via 57 combined sewer overflows (CSO) along the banks of the river.
Today, the population of London is an estimated eight million and Thames Water says that the current system lacks the necessary capacity. Bazalgette's original system does not serve all of these eight million people, as areas in outer London, built later, were provided with separate sewerage and rainwater infrastructure. Overflows have become more and more common and now occur on average 50 times a year. These discharges, of combined raw sewage and rainwater, need to be reduced to comply with the EU's Waste Water Treatment Directive (UWWTD) and to improve the ecology of the river. An estimated total of some 39,000,000 m3 (3.9×1010 l), or 39 million tonnes, of storm sewage enters the river in a typical year.
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 River Thames and to identify objectives and propose potential solutions, while keeping costs and benefits in mind.
After four years, the Thames Tideway Strategic Study report was published in 2005, and outlined the following objectives:
- To protect the ecology of the Tideway;
- To reduce the aesthetic pollution due to sewage derived litter; and
- Protect the health of recreational water users
Four potential strategies were discussed:
- Adoption of source control and sustainable urban drainage;
- Separation of foul and surface drainage and local storage;
- Screening, storage or treatment at the discharge point to river; and
- In-river treatment
After evaluation of the potential strategies it was decided that only one, the screening, storage or treatment at the point of discharge would fully meet objectives. The remainder were found to be either impractical or insufficient to provide a solution, although a number of parties are questioning the validity of this conclusion, in particular relating to the dismissal of SuDS/blue-green infrastructure as a solution. Some groups that oppose the tunnel state that it is an unsustainable 19th century solution to a 21st-century problem. They argue 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
It was decided that the best method of implementing the screening, storage and treatment approach would be a three-pronged solution collectively known as the London Tideway Improvements.
The first part consisted of a deep storage and conveyance tunnel known as the Lee Tunnel and is currently under construction. This 6.9 km (4.3 mi) long tunnel, running up to 75 m (246 ft) deep from Abbey Mills to Beckton, will capture 16,000,000 m3 (1.6×1010 l), or 16 million tonnes, annually from the single largest polluting CSO in London. The construction of the tunnel began in 2010 and is expected to be completed in 2015. Thames Water awarded the construction contract to the MVB JV, made up of Morgan Sindall, VINCI Construction Grands Projets and Bachy Soletanche, in January 2010. The cost is an estimated £635 million.
The second part is the £675M project to modernise and extend London's five major sewage treatment works. This is aimed at increasing capacity at the works so that a greater volume of sewage can be treated, greatly reducing the need for storm discharges to the river. The five treatment works (with planned improvements) are:
- Mogden Sewage Treatment Works – a £140M upgrade to extend sewage treatment capacity by 50 per cent
- Crossness Sewage Treatment Works – a £220M upgrade to extend treatment capacity by 44 percent
- Beckton Sewage Treatment Works – a £190M upgrade to extend treatment capacity by 60 percent
- Riverside Sewage Treatment Works – an £85M upgrade as part of a major scheme to help improve water quality in the River Thames and produce renewable energy on site
- Long Reach Sewage Treatment Works – a £40M upgrade in Dartford, as part of a major scheme to help improve water quality in the River Thames
These upgrade works will also improve the standard to which the sewage is treated at each of the works, further boosting the water quality of the River Thames.
The final part of the London Tideway Improvement plan is another deep storage and conveyance tunnel, which will intercept the outflows from London's most polluting CSOs and direct them to the sewage treatment works for processing before they can enter the river. This part is known as the Thames Tideway Tunnel.
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.
Initially three potential tunnel routes were considered:
- 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.
- 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 1.8 km (1.1 mi) but requiring longer connection tunnels from some CSOs.
- Abbey Mills Route – this route was different from the River Thames and Rotherhithe routes in that it connects the Thames Tunnel to the head of the Lee Tunnel at the Abbey Mills Pumping Station. This would have followed the same route as first two options but then deviated from the river toward Abbey Mills. The main tunnel length would be approximately 9 km (5.6 mi) 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 (as identified in the Thames Tideway Strategic Report). 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 (both online and hard copy), 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 between March 2011 and August 2011. During this phase residents around 11 specific sites were sent letters explaining that these sites were being considered as alternative sites, and inviting residents 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 was held. These were attended by over 800 people. In all 168 comment cards and 147 pieces of site specific correspondence was 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 shorter Abbey Mills Route
- a main tunnel, 23 km (14 mi) long with an internal diameter of 7.2 m (24 ft);
- the direct interception of 21 CSOs;
- the indirect interception of a further 12, and a local solution for the remaining CSO;
- the selection of five out of 52 shaft sites from the final shortlist, including three where main shaft sites are combined with CSO interception sites; and
- the selection of seventeen out of 71 CSO sites from the final shortlist.
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:
- The need for the project and whether a tunnel was the most appropriate solution
- The preferred tunnel route (including the detailed alignment of the tunnel)
- Preferred sites and permanent works (taking into account the feedback received from the first phase of consultation such as the move from greenfield to brownfield sites)
- Detailed proposals for the preferred sites (again taking into account the feedback from the phase one consultation)
- The effects the project would have (as outlined in the preliminary environmental information report)
A total of 1374 feedback forms (online and hard copy), 4636 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/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
- Acton Storm Tanks - main tunnel reception and CSO interception
- Hammersmith pumping station - CSO interception and connection tunnel drive site
- Barn Elms - CSO interception and connection tunnel drive site
- Putney Embankment foreshore - CSO interception and connection tunnel drive site
- Carnwath Road riverside - main tunnel drive and reception and connection tunnel reception site
- Dormay Street CSO- interception and connection tunnel drive site
- King George’s Park - CSO and connection tunnel reception site
- Falconbrook pumping station - CSO and connection tunnel drive site
- Cremorne Wharf Depot - CSO interception and connection tunnel drive site
- Chelsea Embankment foreshore - CSO interception and connection tunnel drive site
- Kirtling Street - main tunnel double drive site
- Heathwell pumping station - CSO interception and connection tunnel drive site
- Albert Embankment foreshore - CSO interception and connection tunnel drive site
- Victoria Embankment foreshore - CSO interception and connection tunnel drive site
- Blackfriars Bridge foreshore - CSO interception site
- Shad Thames pumping station - system modification site
- Chambers Wharf - main tunnel drive and reception site
- Earl pumping station - CSO interception site
- Deptford Church Street - CSO interception site
- Greenwich pumping station - CSO interception and connection tunnel drive site
- King Edward Memorial Park - CSO interception site
- Bekesbourne Street - system modification site
- Abbey Mills pumping station - main tunnel reception site
Proposed design and construction
To build the Thames Tideway Tunnel, five tunnel boring machines (TBMs) will be needed to excavate the main tunnel. It will also require two types of construction sites: main tunnel sites, where the TBM will either be launched or received, and CSO sites, where interception tunnels and a connection culvert will need to be 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, will vary depending on the depth, the amount of flow they need to carry and the geology. The shaft will be a concrete cylinder with an internal diameter ranging from 6 m (20 ft) to 24 m (79 ft) and 20 m (66 ft) - 60 m (200 ft) deep. Ventilation structures at CSO sites to allow air in and out of the shaft will also need to be built. Construction at these sites is expected to take between 2.5 and 3.5 years and once complete each site will be landscaped.
At the main drive sites, four main activities need to take place: shaft construction (where a concrete cylinder 25 m (82 ft) - 30 m (98 ft) in diameter and about 40 m (130 ft) - 60 m (200 ft) deep would need to be constructed), tunnelling preparations (preparing the site for arrival of the TBM), TBM assembly and lowering into the shaft, and driving the TBM to excavate the main tunnel.
As the TBM moves forward precast concrete segments will be brought in and fixed together to create the tunnel wall. Excavated material will then be transported out the tunnel via a conveyor belt and will be processed before being taken off site. In order to minimise disruption, Thames Water have 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, works are expected to take place 24 hours a day.
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, which is a detailed plan for construction of the Thames Tideway Tunnel, was delivered to the Planning Inspectorate on 28 February 2013. From that date, the Inspectorate had 28 days to decide whether the application is 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 were also to make the documents available for scrutiny at six public locations (to be announced later), along the tunnel’s proposed route, three either side of the river.
On 3 June 2013, it was announced that the Secretary of State had appointed five inspectors: Jan Bessell, Libby Gawith, Emrys Parry, Andrew Phillipson and David Prentis, as the Examining Authority to consider any matters arising. As part of this process, interested parties would be able to make representations.
A Preliminary Meeting, open to those who have registered an interest, began on 12 September 2013 at the Barbican Centre. Chaired by the Inspectorate, this will determine how the examination will be carried out. This will include consideration of more detailed hearings on site-specific matters, as well as project-wide issues. Once the Planning Inspectorate has concluded its examination of the application, a recommendation on whether or not to grant approval (by issuing a Development Consent Order) will be submitted to Government ministers to make the final decision. This is expected in autumn 2014.
If consent is granted, preparatory construction work on the project is scheduled to start in 2015, with main tunnelling due to begin in 2016. The target completion date is 2023.
Funding and delivery
Following detailed analysis it was decided that the best means to deliver the project would be through a regulated infrastructure provider (IP) as this would maximise value for money. The IP, originally to be formed through a competitive process starting in the spring of 2013, will hold its own license from the industry regulator, Ofwat, and will 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 firm-up the funding model to secure financial assurances from the government. The subject of taxpayer support for the construction of a tunnel is 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 (former Director-General of OFWAT, the UK water regulator) 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 (allowing for continued service to customers) and another company or financier allowed to take over its activities."
However, procurement for main contractors (who would eventually be contracted to the IP) 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 (OJEU). Following pre-qualification questionnaires, Thames Water will invite shortlisted contractors to tender between November 2013 and April 2014, with preferred bidders announced in early 2015.
Since its initial proposal, questions were raised on the scheme based in its cost, the location of construction sites and duration and associated disruption of the works, and whether a tunnel is actually necessary or indeed the right solution for London and Thames Water customers.
The £4.2bn cost of the Thames Tideway Tunnel project is to be wholly funded 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 huge amounts of debt to its balance sheet reducing its tax payments while at the same time allowing its shareholders to receive large dividends - money they feel should have been spent on the Thames Tideway Tunnel. Thames Water has maintained it has done nothing unusual by raising debts to reduce tax bills and is following conventional practice. It says the money raised was used for essential maintenance and upgrade works, although some have asked questions about how Thames Water has paid so little corporation tax at the same time as distributing funds to its shareholders.
Those living alongside proposed sites are also concerned about the noise, disruption and the potential loss of public space resulting from construction. To address this Thames Water has put together a Code of Construction Practice (CoCP) which outlines both site-specific and project-wide requirements and measures that will be applied to minimise the impacts of the construction and how best practice standards and requirements will be implemented across all sites and contracts. The Code also covers transport (both road and river transport), noise and vibration mitigation, air quality and water resources, land quality, waste management and resource use, ecology and conservation and historic environment.
Tunnel sceptics maintain that sustainable urban drainage solution (SuDS) or green infrastructure would remove the need for the tunnel. By replacing paved, impermeable surfaces in London with permeable options and implementing green roof, 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 also feel that these measures would provide the level of control required whilst being cheaper than the proposed Thames Tideway Tunnel. Green infrastructure would have further benefits for London in addition to addressing the rainwater overflow problem, such as:
- Increased resilience to drought and floods,
- Reduction in urban air pollution,
- Climate change mitigation - contrasted to the tunnel's significant carbon footprint,
- Enjoyment, aesthetics and health benefits of green spaces and nature,
- Reduced urban heat island effect and associated reduction in cooling load and carbon emissions,
- Improved urban biodiversity.
- Earlier avoidance of EU fines for not meeting water standards than under the Scheme.
The earliest customers’ bills could be affected is 2014/15, with charges rising gradually after that. The project is estimated to add a maximum of £70 to £80 to average annual wastewater bills from around 2019 (excluding inflation).
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