The story of the largest canal tunnel in Britain
The idea for building the Thames and Medway Canal sprang from fears that enemy ships might venture into the Thames estuary and attack the naval dockyards at Deptford, Woolwich and Chatham. A canal linking the Thames and Medway would provide a vital, inland emergency supply route between the dockyards. The Tilbury and New Tavern Forts would protect the entrance at Gravesend. The journey for water-borne transports would be shortened from 46 miles to just 7 miles.
The original scheme was abandoned, but revitalised in 1799 when engineer Ralph Dodd put forward another plan to build a canal 48 ft (17.4m) wide by 7 ft (2.5m) deep. He estimated that it would take two years to build and cost £40,000. Many local people subscribed to the new venture and in 1804, 1810 and 1818, bills were passed in Parliament to raise further money.
In 1809 work on the lock to the canal basin at Gravesend began. The lock was 109 feet (33.2m) by 23 feet (7m) and enabled craft of up to 200 tons to enter the basin to offload cargoes onto the barges working the canal itself. The canal included a tunnel that would be Britain’s largest in diameter at 26.5 feet (9.6m) wide including the towpath. The tunnel is 2.5 miles (4.5km) long. The final building cost of the canal was £300,000.
The commercial success of the canal was affected by the fact that the lock could not be extended into the river to enable the entrance to be used at tidal state. In addition, the canal tended to lose 4ft of water between the tides and hence a steam pumping station had to be installed at Gravesend to top the water up. Tolls also had to be set at a high level to try and re-coup some of the costs of the building. In 1825 it cost 2s 6d per ton to transport hops or wool and 1s 2d per ton to transport hay, oats, straw, etc. By 1840, the shareholders decided that would be more profitable to build a railway. The canal basin continued to be used as it was just outside the limit of the Port of London and so it was not necessary to pay the heavy London dues on coal. Several coal wharves were built and an electricity station and gasworks situated nearby. The canal was finally abandoned in 1934 and the basin was bought by Gravesham Borough Council in 1970 with a view to restoration.
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