Engineers are using archaeological techniques to unearth the secrets of Thirlmere Aqueduct.

Sophisticated radar technology, used to find buried treasures, is being used to inspect the 84-mile underground tunnel which brings water from the Lake District to Manchester.

Work on the tunnel, built to serve the water needs of Manchester's cotton industry, began in 1885. Parts of the aqueduct were hewn from solid rock, while others were constructed by Victorian builders.

Inspection

The high-tech inspection is the latest phase in a six-year, £12m overhaul of the pipeline by United Utilities.

Early indications suggest the tunnel only needs a few repairs, and soon the northern part of the pipeline should be ship-shape.

The investigations have helped engineers dispel a local legend around the construction of the aqueduct.

United Utilities' operations manager John Butcher said: "The section of aqueduct under Dunmail Raise is one of the earliest to be constructed and was hewn from the solid rock of the mountain by tunnelling teams who started on opposite sides of the pass and met in the middle.

'Legend'

"Legend has it the two tunnelling teams met spot on in the centre of the mountain, but it looks like they were probably about eight inches out.

"It's still pretty impressive given the technology they had available at the time."

The acqueduct has no pumps along its route, and is the longest gravity-fed aqueduct in Britain.

Every mile the water drops 20 inches.

Mr Butcher said: "The Victorians definitely knew what they were doing. But there is some work that we can do to make it last another 100 years."