Analysis: Digging in for the tunnel

This month digging begins on the Thames Tideway Tunnel. But is the mega-project even needed? And will it keep to plan? Lois Vallely speaks to Tideway chief executive Andy Mitchell to find out.

Enabling works have been going on for months, and within weeks Tideway will start digging the shafts of the Thames Tideway Tunnel. The first thing that needs to be done is diaphragm walling (the construction of vertical walls using deep trench excavations), and this will commence first at Blackfriars.

But is the £4.2 billion tunnel needed at all? Staunch critics such as the Thames Blue Green Economy group say not.

In a report earlier this year, the group called the tunnel an “outdated and expensive folly” and insisted cheaper blue-green solutions were available. Tideway chief executive Andy Mitchell tells Utility Week that although “philosophically” there are alternatives, logically there are not.

Tideway maintains that the tunnel is “urgently needed” to prevent tens of millions of tonnes of raw sewage polluting the tidal River Thames every year.

The aim of the tunnel is to provide capture and storage of nearly all the raw sewage and rainwater that discharges into the River Thames when the system is overloaded. In total, the tunnel will have a volume of 1.6 million cubic metres.

When it rains in London, Beckton sewage treatment works – the largest in Europe – “cannot keep up”. The tunnel is designed to store all the storm water from these outflows when it rains heavily, allowing Beckton to process it at a slower rate.

As weather in the UK worsens and occurrences of heavy rainfall become more frequent, Tideway believes that even with 1.6 million cubic metres of storage capability, sewage may still flow into the river two or three times a year.

Mitchell says that to replicate what the tunnel will accomplish would require blue-green solutions on an “enormous” scale. “You’re talking tens and tens of billions of pounds.”

He adds that the point at which this became a binary argument was “a bad day”, because it should never have been either/or, it should have been both. “If you were starting a city from scratch, you obviously wouldn’t throw perfectly good rainwater in the sewer – that’s ridiculous. When people are designing and building new cities, they don’t do that any more.

“London has got to understand how to get more water-sensible as we go forward – but that is all about mitigating a future deterioration. To be a replacement to the tunnel just practically isn’t viable. It’s a bit of a silly debate really.”

Many big infrastructure projects – Hinkley Point C being the most obvious example – are struggling both with deadlines and budget. However, Tideway is adamant that its project will be completed on time and on budget. Mitchell tells Utility Week the company has a back-up plan.

A schedule-risk analysis carried out before work began showed there was a “foreseeable possibility” that the job would take a year longer than the schedule. And, Mitchell says, that is still the case.

However, the company has a target of completing the project two years early. “We’ve been pursuing that from the beginning. We mobilised on all of our sites early,” he says. So even if hitches cost it a year, it will still finish a year early.

“Chasing an earlier programme, we find it very difficult to see how we’ll overrun on time and therefore how we’ll overrun on cost,” he adds. “We’ve got no intention of running over on either.”

Mitchell says there “truly has never been a better time to build the Thames Tideway Tunnel”. With all of the learnings taken from previous projects, and rich experience within the team, he concludes: “There is no reason for us to believe anything other than that we will do what we set out to do.”

Case study: Crossrail

Crossrail is a major construction project expected to increase rail capacity in central London by 10 per cent, significantly reducing congestion on the London Underground.

The route will pass through 40 stations from Reading and Heathrow in the west, through new twin-bore 21km tunnels to Shenfield and Abbey Wood in the east.

The Transport for London (TfL) run railway will be named the Elizabeth line when services through central London open in December 2018. The Crossrail project is being delivered by Crossrail Limited, a wholly owned subsidiary of TfL, and is jointly sponsored by the Department for Transport and TfL.

Since the construction of the new railway began in 2009, more than 15,000 people have worked on the project, and more than 100 million working hours have been completed.

Following the comprehensive spending review in October 2010, funding of £14.8 billion was agreed to deliver the Crossrail scheme.

Read a Q&A with Thames Tideway Tunnel chief executive Andy Mitchell here.