The Shrewsbury Canal connected Shrewsbury to the Wombridge Canal, and provided a way to supply the people of Shrewsbury with coal at reasonable prices. The route between Shrewsbury and Wappenshall was relatively flat, although beyond Wappenshall, nine locks and a large inclined plane were needed to reach the Wombridge Canal. There were two more locks before Wappenshall. The valleys of the River Tern and the River Roden were crossed by aqueducts, Longdon-on-Tern Aqueduct being, in Thomas Telford's opinion, the first aqueduct made of cast iron, although Benjamin Outram's iron aqueduct on the Derby Canal actually opened a month earlier. The other major obstacle to a level canal was a bluff of land near a large bend in the River Severn just to the east of Shrewsbury. A route closer to the river might have been possible and would have avoided a tunnel if a large landscaped park had not been created there in 1786, to the design of Humphry Repton.
Josiah Clowes was the engineer for the canal from the start of its construction until his death in 1795, and the tunnel was his design. However, William Reynolds, the iron founder responsible for the manufacture of the iron aqueduct, suggested that a towpath should be provided throughout its length. The tunnel was around 10 feet wide, and the wooden towpath was fixed to bearers built into the wall. It was 3 feet wide, but because the entire width of the tunnel was filled with water, including the bit below the towpath, the resistance to boats passing through the tunnel was reduced. The structure was 970 yards long, and was the first tunnel to be constructed with a towpath. Tunnels without a towpath were arduous for the crews, as the boats had to be legged through them.
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