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Netherton Tunnel Branch Canal, in the English West Midlands, is part of the Birmingham Canal Navigations, (BCN). It was constructed at a 453–foot elevation, the Wednesbury or Birmingham level; it has no locks. The total length of the branch canal is and the canal tunnel is long. Netherton Tunnel was the last canal tunnel to be built in Britain during the Canal Age. The first sod was turned by the Lord Ward on 31 December 1855 and the canal opened on 20 August 1858, providing a waterway connection between the Black Country towns of Netherton and Tipton. It was built to relieve the bottleneck of the adjacent Dudley Tunnel which is very narrow, has alternating blocks of one-way working, and had waiting times of eight hours or more, and sometimes several days. The Netherton tunnel was built with a width of to allow two-way working of narrowboats; and is brick lined throughout. It has towpaths running through it, one on each side, which enabled horse-drawn narrowboats to be pulled through it. Chainage (distance) markers are still visible on the Eastern wall. The tunnel was fitted, from the start, with gas lighting over the towpaths, though this was later converted to electricity and it is now unlit. The air vents that run along the line of the tunnel and provide ventilation, and a shaft of light into the canal, are known by the locals as "pepper pots", because of their shape. They are brick-lined and the openings are covered by an iron frame or grill. The wide bore and good ventilation mean that boats using the tunnel today are allowed to use the power of their internal combustion engines, which is prohibited in the narrower Dudley Tunnel. The tunnel cost £302,000 as opposed to the £238,000 estimate prior to construction. The main reason for the project being overbudget was the extra works necessitated by the condition of the ground through which the tunnel passes.〔Roger Cragg, 1997. ''Wales and West Central England: Wales and West Central England, 2nd Edition''. Thomas Telford (ISBN 0-7277-2576-9)〕 == Repairs == In 1983, the British Waterways Board had of the brick invert replaced with concrete as a result of the invert rising sufficiently to impede navigation.〔"Repairers wary in Netherton heaving invert", ''New Civil Engineer'', 1983, 30 June.〕 In 2011, significant cracks were found in part of the tunnel lining. Traffic through the tunnel was limited, as a result.〔 Repair work began early in 2013. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Netherton Tunnel Branch Canal」の詳細全文を読む スポンサード リンク
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