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The Standedge Tunnel is well known for being the longest, deepest and highest canal tunnel in Britain.
It is 5,500 yards long, 638 feet underground at the deepest point and 645 feet above sea level.
Outram thought that the hill was gritstone and strong shale and would not present any difficulties. More than the expected amount of water entered the workings and a lining was going to be needed which pushed up the construction costs considerably. Work on the tunnel was difficult and progress very slow. Gunpowder had to be used to blast through the solid rock.
In 1801, Outram resigned from his post and Thomas Telford was called in to advise on the tunnel's completion.
The tunnel finaly opened in 1811, at last providing a through route 13 years after the rest of the canal had been completed and 17 years after work first began, at a cost of £123,803.
Between 1811 and 1840 the tunnel was used on average by 40 boats daily. The Huddersfield Narrow Canal was purchased by the former Huddersfield and Manchester Railway in 1846. The canal tunnel proved most beneficial in assisting with the construction of the first railway tunnel at this location, as no vertical shafts were needed in the construction and the canal was an easy way to help remove the large amount of spoil excavated. Several cross-passages were retained.
The last commercial boat to use the tunnel was in 1921, and the canal officially closed in 1943, after which it soon fell into disrepair. The tunnel became unsafe with several rockfalls inside, and was closed off by large iron gates at each end.
When restoration started as part of an effort to re-open the entire Huddersfield Narrow Canal, several rock-lined parts of the tunnel were found to be unstable. These were stabilised by rock bolts, and in places, the rock face was lined with special concrete.
The tunnel re-opened in May 2001.
When the canal was reopened it was felt that it would not be safe for boaters to navigate the tunnel under their own diesel power, due to the length of the tunnel and the lack of ventilation. Instead, BW operate electric tug boats to pull boats through.
This has now been changed and boaters navigate the tunnel under their own power.