The ‘super-sewer’ reconnecting Londoners with the Thames

As one major infrastructure project, Crossrail, approaches the end of the line, another is just about to embark on a defining year as Thames Tideway prepares to launch tunnel-boring machines (TBMs) in a matter of weeks for the construction of a 25km ‘super-sewer’.

The £4.2bn Thames Tideway Tunnel scheme is being constructed to tackle the problem of sewage pollution in the River Thames with the promise of “reconnecting Londoners” by preventing millions of tonnes of untreated sewage flowing into the Thames each year. It is the largest infrastructure project ever undertaken by the UK water industry and will rid sewage to levels never seen for 250 years - before humans started polluting it.

Tideway will employ up to 4,000 employees across 24 sites of various sizes, stretching from Acton in the west to Abbey Wood in the east and is entering a major milestone moment. The sewer’s connection is being split into three parts; with contractors Bam Nuttall, Morgan Sindall and Balfour Beatty carrying out the work in the west section; Ferrovial and Laing O’Rourke centrally; and Costain Vinci and Bachy Soletanche in the east.

The end of summer is being pencilled in as the start of the much-anticipated tunnelling process with 1,300 tonne TBM’s lowered 53m deep at the organisation’s central site in Battersea. It is currently a hive of activity with the main focus on assembling gigantic sections of the machines which currently sit in the yard. The TBMs named Millicent and Ursula, will measure more than 100m long when fully assembled. The first shipment made the 500-mile journey at the start of February from the across the Channel after being built in Le Creusot, France.

Lessons learned from Crossrail

While Tideway gears up for the major tunnelling process, Crossrail has not long finished completing their own excavation work. Those behind the massive water project say there are “lots of lessons to be learnt” from their counterparts with many involved in the rail project now adding similar knowledge and expertise to Tideway.

Michael Appleton, communications lead for the central section of Tideway, said: “Construction is a continuous improving process. It’s all about finding new and better ways of doing things. Anything you can glean from other projects is priceless and something you should be doing. The experience of Crossrail has been invaluable with things like stakeholder engagement, skills we need as well as the construction process. For example, one of the complaints from Crossrail was that the control box within the TBMs was not big enough so we have increased the size of it and that is just one small practical example of a lesson learnt.”

The TBMs were transported along the Thames to keep in line with Tideway’s commitment to transport over 90% of waste by barge and will result in reducing the amount of trucks on the project by 72%. Sustainability was highlighted as a key target from the very start by Tideway. If bosses behind the project decided to transport everything by road then approximately half a million truck movements would be made. 

The tunnel itself will work by intercepting sewage from 34 Combined Sewer Overflows (CSO) before it moves into the Thames. The CSO discharge points will be connected to the tunnel under the river and rather than flowing into the Thames, the dirty water will be stored in the sewer. It will then be pumped to the Beckton Sewerage Treatment Works and once treated, the clean water will be finally released into the river.

Huge challenges ahead

The task at hand is a huge one that requires constant collaboration and communication between the various teams on site. But the project remains on schedule with workers managing to negate challenges arising.

“There are always huge challenges when it comes to a project like this,” Appleton said. “Crossrail used to say that a project like that in central London is like doing open heart surgery on a person still walking round and its very similar here. It’s always things that you are not prepared for which crop up, so last year we found a Second World War explosive bomb which we believe rolled into the site from the tide. It’s those sorts of things which can throw your plans out of kilter,” he says.

Another big marker in the project this year has been the start of diaphragm walling at the Greenwich pumping station construction site in preparation for digging the tunnel shaft which will be constructed from the Greenwich through to Tideway’s Chambers Wharf site. The concrete structure diaphragm wall will be inserted into the ground and will maintain an excavation open, which is described as an essential element of digging a tunnel shift.

Tideway delivery manager Jim Avant said: “After several months of hard work the completion of the diaphragm wall works at Chambers Wharf marked a significant milestone for the project. It was no mean feat, around 35,000t of material excavated during the works, all of which was removed from site by barge in line with Tideway’s commitment to remove as much material as possible by river. Similarly, all reinforcement cages for the walls have been delivered to site by barge.”

Community engagement

Like any other major project that runs through the heart of a city and near the homes of residents, community relations play a vital part. The ability for teams to lessen the environmental, noise and visual impacts when possible can make or break how a development is perceived and accepted. 

Trigger Action Plans have been a crucial component of keeping people on board from the start with Tideway prepared to listen to its neighbours across London. For example, discussions have been had when residents will have been told a noise limit and if work was to go over that level then Tideway would provide the necessary mitigation in the form of secondary glazing or mechanical ventilation. Regular community meetings which give people the opportunities to air their views have also been commonplace. Maintaining good links with the community has been “absolutely vital” according to Appleton.

“Community relations can be very much misunderstood but I think Tideway gets it right,” he added. “We are not as controversial as other projects in London and I think that is helped by our approach. There will be times when we make noise but that is a fact of construction but we have done is try to be fair to people with mitigation and compensation.”

A monumental year for the project

But as work progresses across various sites, 2018 has been dubbed as a monumental year for the project and once that will go a big way in defining how much of a success it is.

Andy Mitchell, Tideway’s chief executive officer, said: “This is going to be a big year for Tideway and we’re working hard to get tunnel shafts completed in preparation for the start of tunnelling later this year. The arrival of Tideway’s second and third TBMs was another exciting milestone, signalling that work is gearing up on London’s super sewer.” 

Tideway’s strapline is “reconnecting Londoners to the Thames” and that is exactly what the lasting legacy is hoped to be so that the general public won’t simply use the river for transportation but enjoy it as the asset it once was for the capital.

“The aim is a cleaner and healthier River Thames,” Appleton said. “We are not entirely sure what will happen with a cleaner Thames as no one has any experience of that. For the past 500/600 years it’s been polluted so we can’t say ecologically what that will look like. I envisage people using the river more. 

“If you talk to rowers down at Putney then they say if they fall in, they have to go to A&E because you end up with all sorts of diseases. The attitude to the river in the past has been almost something of an obstacle or inconvenience. But really, it’s the reason we are here and is the lifeblood of London so cleaning it up is really important. People don’t use the river as a place to enjoy and allowing Londoners to reconnect with the river will be the lasting legacy,” says Appleton.