The Shrewsbury Canal (or Shrewsbury and Newport Canal) was a canal in Shropshire. Authorised in 1793, the main line from Trench to Shrewsbury was fully open by 1797, but it remained isolated from the rest of the canal network until 1835, when the Birmingham & Liverpool Junction Canal built the Newport Branch from Norbury Junction to a new junction with the Shrewsbury Canal at Wappenshall. After ownership passed to a series of railway companies, the canal was officially abandoned in 1944; many sections have disappeared, though some bridges and other structures can still be found. There is an active campaign to preserve the remnants of the canal and to restore the Norbury to Shrewsbury line to navigation.
Josiah Clowes was appointed Chief Engineer, but died in 1795 part way through construction. He was succeeded by Thomas Telford, then just establishing himself as Shropshire's County Surveyor and already engaged on the Ellesmere Canal slightly further north.
One of Telford's first tasks was to rebuild a stone aqueduct over the River Tern at Longdon-on-Tern which had been built by Clowes but swept away by floods in February 1795. Telford's stone-mason instincts initially led him to consider replacing the original structure with another stone-built aqueduct, but the heavy involvement of iron-masters in the Shrewsbury Canal Company, notably William Reynolds, led him to reconsider. Instead, it was rebuilt using a 62-yard (57 m) cast iron trough cast in sections at Reynolds' Ketley ironworks and bolted together in 1796. The main trough was 7.5 feet (2.3 m) wide and 4.5 feet (1.4 m) deep, with a narrower trough to one side which formed the towpath. The aqueduct was the world's first large-scale iron navigable aqueduct, though it was narrowly predated by a much smaller 44-foot-long (13 m) structure on the Derby Canal built by Benjamin Outram.
The aqueduct still stands today, though it is isolated in the middle of a field. This successful use of an iron trough to contain the water of a navigable aqueduct casts the Tern aqueduct in the role of Telford's prototype for the much longer Pontcysyllte Aqueduct on the Llangollen Canal, where he mounted the iron trough on high masonry arches.