Canal Tunnels

Building tunnels was probably the most difficult engineering task facing the early canal builders. They avoided them wherever possible, taking winding routes around hills, as on the Oxford Canal, or climbing up and over the hills. However both increased journey times, and the extra locks often led to water shortages at the higher levels.

Tunnels were usually built by laying out the straight route across the hilltop and then sinking a number of shafts. The shafts were aligned on the surface using a telescope. Digging began in both directions from the bottom of all the shafts, and from the tunnel entrances. Surveying techniques were basic at first, using plumblines. The early tunnellers were miners who were not used to taking accurate headings, so the horizontal shafts sometimes didn't meet up correctly, Saltersford tunnel has an obvious sharp kink in it.

Tunnels were usually brick lined but subsidence frequently caused problems, closing a number of tunnels including Lapal on the Birmingham system and the original Harecastle Tunnel, and requiring lengthy repairs as at Blisworth and Preston Brook.

However the reopening in 2001 of the Huddersfield Narrow Canal has given Standedge Tunnel back its 'longest uk canal tunnel' title at 5456 yards. Sapperton (3817 yards) and Lappal (3795 yards) are both closed, though the former is scheduled for restoration.