11:07am Friday 27th October 2006
By Mike Addison
A secret underwater world connecting the Lake District to more than a million homes in the North West has been revealed for the first time.
United Utilities engineers have made history by completely draining the 134km-aqueduct between Thirlmere and Bolton, enabling inspection teams to walk through it from end to end and give it a thorough health check.
The last time the aqueduct would have been completely empty along its entire length would have been when it was built more than 100 years ago.
United Utilities project manager Gareth Wheatley said: "We've been literally walking in the footsteps of our Victorian forebears. It's been a fascinating experience."
The aqueduct first supplied Manchester's water in 1894 and, when full, carries more than 200 million litres of water a day from Thirlmere to United Utilities' treatment works near Bolton.
There are no pumps on the aqueduct and water takes just over a day to reach Manchester, making the journey at around 4mph and falling at 20 inches per mile.
"It's a real feat of engineering and a testament to the skill of the Victorian engineers that it's provided unbroken service all this time," said Mr Wheatley.
"In the old days we'd have just taken sections at a time out of service or used dinghies to inspect the inside but we wanted to give it a proper floor-to-ceiling once-over this time and the only way we could do that was to empty it properly and walk through," he added.
It has taken the specialist inspection teams four weeks to carry out their work, dropping into the aqueduct at more than 70 locations between the north of the region and the south.
And their work followed months of preparation behind the scenes, ensuring that water could be brought in from other sources to keep the taps flowing.
Mr Wheatley added: "This whole job is a huge technical challenge and it's funny to think that a mark of our success so far has been that customers haven't noticed anything different!"
The inspections are due to finish next week, when the aqueduct will be brought back into full service.
United Utilities engineers will then begin the painstaking work of analysing all the inspection teams' data.
The whole scheme is one of the largest the company has ever undertaken and the largest project of its kind in Europe.
Over the next eight years, the £350 million project will see more than 800km of major water mains inspected, cleaned and repaired.
Mr Wheatley added: "Water quality in the North West is the best it's ever been but that doesn't happen by accident. We have to work hard to maintain that and this project will ensure we can protect our vital mains for the next generation.
"We'll be back next year, draining the aqueduct down again, this time to carry out any necessary maintenance and repair work," he said.
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