First Vyrnwy Aqueduct
This aqueduct is largest structure on the Montgomery Canal. It crosses the River Vyrnwy, south west of Llanymynech.
Difficulties during construction of the masonry aqueducts at Vyrnwy and Berriew led to parts of the structures collapsing. The engineer, John Dadford, resigned in 1796, and was replaced by his father Thomas Dadford senior (1730-1809). William Jessop was also called in to advise on remedial works.
1797 After 26km of the canal had been built, funding ran out and construction halted.
During the 1820s, the Vyrnwy Aqueduct underwent extensive repairs with cast iron strengthening bars.
Second Vyrnwy Aqueduct
A second Vyrnwy Aqueduct was built, starting in 1881, to carry water to Liverpool from Lake Vyrnwy. Originally it consisted of a single pipeline, constructed generally of 1.07m diameter cast iron tubes but where the route crossed the River Mersey the pipeline was of 813mm diameter riveted steel to facilitate maintenance; similarly the river Weaver was crossed by steel tubes. In both cases the tubes were in tunnels beneath the rivers.
Its route follows the watershed of the rivers Dee and Severn, maintaining high ground through Hirnant, Oswestry, Malpas and Cotebrook. It then crosses the basins of the rivers Weaver and Mersey to finish at Prescot service reservoirs, east of Liverpool, for onward distribution. The construction entailed tunnels, balancing reservoirs, valve houses, and river and railway crossings. The Norton water-tower, near Runcorn, was built to hold a balancing reservoir at height above the Aqueduct.
1892 The Aqueduct was said to be the longest in the world when it was opened, conveying the waters of the largest artificial lake in Europe to Liverpool.
Increasing the capacity of the Vyrnwy Aqueduct
1926 The aqueduct carrying water from Lake Vyrnwy to Liverpool is divided into a number of sections, of which the upper section, between Vyrnwy and Oswestry, carried unfiltered water. That section (21km in length) was a double line of 160cm diameter pipes, with capacity less than that of the sections below Oswestry. At the beginning of year the Water Committee of Liverpool Corporation decided to start work to increase capacity of part of the aqueduct between the lake and Oswestry by adding an extra pipe of 7km length in parallel with the existing line
Sources of Information
- Engineering timelines 
- The Engineer 1927/01/07
- Engineering timelines