Barrelled Lock Chamber, Sea Walls, Swing Bridge, Locks And Canal Basin

This canal infrastructure dates from 1799–1801, designed by civil engineer Ralph Dodd, with a late 19th-century swing bridge and probably 20th-century lock gates added later. The complex comprises the only currently navigable section of the Thames and Medway Canal. Late 20th-century wooden panelling to part of the western side of the northern canal basin and late 20th-century concrete sheet piling to various sections around the basin are not included in the listing.

Construction and Materials

The walls are mainly built of yellow and brown brick laid in English bond, with deep York stone coping and quoins. In places they have been patched with 20th-century engineering bricks. The canal basin reportedly has a paved floor. The swing bridge, lock gates and their mechanisms are of cast iron, with a wooden floor to the swing bridge and wooden lock gates.

The Lock Chamber and River Frontage

The River Thames frontage features curved sea walls leading directly into the barrelled lock chamber, which is unusual in having a curved shape—designed partly to match ships' hulls. The northwest side wall displays a series of Roman numerals by the locks indicating water depth. The extreme north of the northeastern side of the lock chamber has been strengthened with late 20th-century concrete and sheet piling.

The Swing Bridge

At the northern end stands a cast-iron riveted swing bridge with flat arch and cast-iron handrail. It remains operational, turned by a circular cast-iron winch mounted on a three-legged pedestal. The northern lock gates were blown off by enemy action during the Second World War and never replaced.

The Southern Lock Gates

The southern lock gates comprise two panelled wooden gates, probably of 20th-century date, with a cast-iron walkway above featuring painted cast-iron balustrading. They are operated by four winches with intact mechanisms in cast-iron housings.

The Lock Basin and Canal Basin

The southern end of the lock basin leads into the canal basin. On the west side is a section of curved and battered brick walling with stone coping. To the east it curves into the northeastern wall of the canal basin, becoming a straight battered section of brick with stone coping. At the eastern end this curves into what was originally a lock between the lock basin and the canal, now blocked off.

This former entrance to the canal forms the eastern side of the canal basin, which has curved walls on both north and south sides. Each side retains the curved stone slot for the original lock gates and cast-iron remains of the opening mechanism. The eastern side of the south side of the canal basin is a straight section angled to the southeast with several iron mooring rings set into the stone coping.

Apart from a small section of brick walling on the western side of the north side of the canal basin (forming the southern entrance to the lock basin), the remainder of the canal basin was simply excavated from the chalk and had no brick or masonry walls.

Historical Background

Work on the Thames and Medway Canal basin began in 1799 during the wars with Revolutionary and later Napoleonic France. The canal was originally designed to provide a safe route for ships and barges from the Deptford and Woolwich Dockyards carrying ordnance to men-of-war at Chatham, avoiding the considerable danger from French privateers operating in the Thames estuary. A further advantage was that ships would be saved the 47-mile passage around the Isle of Grain, which would be reduced to just over six miles.

Civil engineer Ralph Dodd published a pamphlet in 1799 advocating a six-mile canal between Gravesend and Chatham with locks and basins. He estimated it would take two years to build and cost £24,576. Part of the cost was to be met by selling the excavated chalk as agricultural lime. Dodd considered the canal would be useful not only to the government but would also attract commercial vessels.

In 1800 the canal company received the necessary Act of Parliament and work began at the Gravesend end. The estimated cost had by then reached £57,433. From the Gravesend basin the canal began with a straight section aligned with New Tavern Fort, Gravesend. By 1801 four miles had been constructed as far as Higham. A new engineer, Ralph Walker, announced that the whole canal would cost much more than the revised estimate. Work was stopped and by 1804 Richard Dodd had probably left the project.

Over the next few years Walker suggested two new routes for the Higham to Strood stretch, for which Acts of Parliament were obtained and money raised. The approved route required a tunnel through the chalk hills 3,946 yards long. Work on this did not start until 1819 and it was designed by William Tierney Clark. The Higham Tunnel was over 26 feet wide and 35 feet high—the second longest canal tunnel built in Britain but with the largest cross-section.

The canal finally opened on 14 October 1824, completed by William Tierney Clark, but by that time the Revolutionary and Napoleonic wars were long over and the military need had greatly diminished. The canal had required five Acts of Parliament and cost about £260,000.

Despite a steady trade in agricultural products, beer, cement and groceries, the canal was never a financial success. There were technical problems because the canal walls leaked and the water level dropped every spring tide. In February 1844 the company built a single-track railway alongside the canal which was brought through the Higham Tunnel, supported on timbers over the water. Eighteen months later the Higham Tunnel was sold to the South Eastern Railway, who filled in the canal from Higham to Frindsbury.

The stretch of canal from Gravesend to Lower Higham remained navigable into the 1930s but was officially abandoned in 1934. In the Second World War some of London's bomb rubble was brought in to infill parts of the canal and the outer lock gate of the lock chamber was blown off by enemy action. The canal has mostly been filled in apart from the Gravesend canal basin and a small section downstream between it and the Higham Tunnel.

Cartographic Evidence

The 1874 Ordnance Survey map shows the canal basin at its present extent with shaded lines to the western part of the north side, west side and western part of the south side, indicating chalk excavation edges rather than brick and masonry edges. A drawbridge is shown passing over the lock basin to the north of the canal basin, which is shown with two locks. A further lock with lock gates is shown at the eastern end of the canal basin where it entered the canal. The only change recorded on the 1897 Ordnance Survey sheet is that the drawbridge over the lock chamber is now called a swing bridge, a change repeated on the 1909 and 1936 maps.