Water company sheds light on invisible tunnel: The pounds 250m Thames Ring Main is the capital's best-kept secret, reports Martin Whitfield

THE invisibility of Britain's longest tunnel is both the secret of its success and the reason that at least 90 per cent of the public does not know it exists.

Lying deep below the streets of London, the 50-mile long Thames Water Ring Main is one of the capital's biggest engineering feats, taking eight years and pounds 250m to complete.

But above ground there is nothing. Not even a hint of the huge pumping stations, built 40 metres underneath Park Lane, the Holland Park roundabout and Barrow Hill, next to Regent's Park.

People who live near the 21 access shafts may have been aware of the construction but most others had little idea of what was going on beneath their feet.

To rectify the ignorance, Thames Water is spending some of the savings the Ring Main will deliver ( pounds 2m a year off the pumping electricity bill alone) on an advertising campaign to sing the project's praises to customers. The Queen will officially open the main on 11 November.

'Most people have no idea of the work that goes into delivering water in the taps,' Mike Dick, principal construction engineer, said. Many of the capital's residents were only too aware of one of the main reasons for the Ring Main's construction - burst water pipes that caused serious traffic congestion.

The system of surface water mains, buried a few feet under arterial roads, remains largely a Victorian network placed under ever increasing pressure from higher demand and rising traffic.

About three-quarters of London's water comes from the Thames but pollution in the 19th century led to legislation saying that no drinking water could be extracted downstream from Teddington, well to the west of the city.

Water is drawn from the river to the large reservoirs at Hampton, Ashford, Stanwell and Wraysbury before being cleaned and then pumped to customers in central London.

It was the expense and failure of this pumping system that necessitated the building of the Ring Main, a circular tunnel wide enough to take the average family saloon with plenty of room to spare. It carries half of the capital's drinking water.

Built at a depth of 40m from where the water enters the system in west London, the flow is by gravity to central London pumping stations, so cutting the need for expensive pumping.

The water is raised at 11 pumping stations to join the distributor pipes at the surface.

Because it is a circular tunnel, water can flow in either direction. A section can be closed for maintenance and water sent in different directions to either side of the break in order to guarantee continual supply.

Most of the main, built in phases since 1986, is now working, with just a small section to be completed near the Ashford Common treatment works.

'It means there is now less pressure on the surface mains, many of which are 100 years old. We will be able to look at some for the first time because they were too important to be taken out of service,' Mr Dick said.

Later phases of the project followed the construction of Channel tunnel and workers and equipment came from Folkestone. Burrowing through London clay, the work is straightforward in tunnelling terms although the ground at Tooting Bec Common, which is Thanet sand, had to be frozen first.

The tunnelling crews have not had far to go for the next job - London Underground's Jubilee Line extension.

(Photograph omitted)

Start your day with The Independent, sign up for daily news emails
PROMOTED VIDEO
Have you tried new the Independent Digital Edition apps?
ebooks
ebooksA special investigation by Andy McSmith
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Tradewind Recruitment: PMLD Teacher

Negotiable: Tradewind Recruitment: PMLD Teacher A specialist primary school i...

Recruitment Genius: Online Media Sales Trainee

£15000 - £30000 per annum: Recruitment Genius: Now our rapidly expanding and A...

Recruitment Genius: Public House Manager / Management Couples

£15000 - £20000 per annum: Recruitment Genius: Are you passionate about great ...

Recruitment Genius: Production Planner

£20000 - £30000 per annum: Recruitment Genius: This fast growing reinforcing s...

Day In a Page

As in 1942, Germany must show restraint over Greece

As in 1942, Germany must show restraint over Greece

Mussolini tried to warn his ally of the danger of bringing the country to its knees. So should we, says Patrick Cockburn
Britain's widening poverty gap should be causing outrage at the start of the election campaign

The short stroll that should be our walk of shame

Courting the global elite has failed to benefit Britain, as the vast disparity in wealth on display in the capital shows
Homeless Veterans appeal: The rise of the working poor: when having a job cannot prevent poverty

Homeless Veterans appeal

The rise of the working poor: when having a job cannot prevent poverty
Prince Charles the saviour of the nation? A new book highlights concerns about how political he will be when he eventually becomes king

Prince Charles the saviour of the nation?

A new book highlights concerns about how political he will be when he eventually becomes king
How books can defeat Isis: Patrick Cockburn was able to update his agenda-setting 'The Rise of Islamic State' while under attack in Baghdad

How books can defeat Isis

Patrick Cockburn was able to update his agenda-setting 'The Rise of Islamic State' while under attack in Baghdad
Judith Hackitt: The myths of elf 'n' safety

Judith Hackitt: The myths of elf 'n' safety

She may be in charge of minimising our risks of injury, but the chair of the Health and Safety Executive still wants children to be able to hurt themselves
The open loathing between Barack Obama and Benjamin Netanyahu just got worse

The open loathing between Obama and Netanyahu just got worse

The Israeli PM's relationship with the Obama has always been chilly, but going over the President's head on Iran will do him no favours, says Rupert Cornwell
French chefs get 'le huff' as nation slips down global cuisine rankings

French chefs get 'le huff' as nation slips down global cuisine rankings

Fury at British best restaurants survey sees French magazine produce a rival list
Star choreographer Matthew Bourne gives young carers a chance to perform at Sadler's Wells

Young carers to make dance debut

What happened when superstar choreographer Matthew Bourne encouraged 27 teenage carers to think about themselves for once?
Design Council's 70th anniversary: Four of the most intriguing prototypes from Ones to Watch

Design Council's 70th anniversary

Four of the most intriguing prototypes from Ones to Watch
Dame Harriet Walter: The actress on learning what it is to age, plastic surgery, and her unease at being honoured by the establishment

Dame Harriet Walter interview

The actress on learning what it is to age, plastic surgery, and her unease at being honoured by the establishment
Art should not be a slave to the ideas driving it

Art should not be a slave to the ideas driving it

Critics of Tom Stoppard's new play seem to agree that cerebral can never trump character, says DJ Taylor
Bill Granger recipes: Our chef's winter salads will make you feel energised through February

Bill Granger's winter salads

Salads aren't just a bit on the side, says our chef - their crunch, colour and natural goodness are perfect for a midwinter pick-me-up
England vs Wales: Cool head George Ford ready to put out dragon fire

George Ford: Cool head ready to put out dragon fire

No 10’s calmness under pressure will be key for England in Cardiff
Michael Calvin: Time for Old Firm to put aside bigotry and forge new links

Michael Calvin's Last Word

Time for Old Firm to put aside bigotry and forge new links