Locks (water Transport) - Pound Lock

A pound lock is a type of lock that is used almost exclusively nowadays on canals and rivers. A pound lock has a chamber (the pound) with gates at both ends that control the level of water in the pound. In contrast, an earlier design with a single gate was known as a flash lock.

Pound locks were used in medieval China during the Song Dynasty (960–1279 AD), having been pioneered by the government official and engineer Qiao Weiyo in 984. They replaced earlier double slipways that had caused trouble and are mentioned by the Chinese polymath Shen Kuo (1031–1095) in his book Dream Pool Essays (published in 1088), and fully described in the Chinese historical text Song Shi (compiled in 1345):

The distance between the two locks was rather more than 50 paces, and the whole space was covered with a great roof like a shed. The gates were 'hanging gates'; when they were closed the water accumulated like a tide until the required level was reached, and then when the time came it was allowed to flow out.

The water level could differ by 4 feet (1.2 m) or 5 feet (1.5 m) at each lock and in the Grand Canal the level was raised in this way by 138 feet (42 m).

In medieval Europe a type of pound lock was first built in 1373 at Vreeswijk, Netherlands. This pound lock serviced many ships at once in a large basin, yet the true pound lock (i.e. one for a small basin) came in 1396 with the one built at Damme near Bruges. A famous civil engineer of pound locks in Europe was the Italian Bertola da Novate (c. 1410–1475), who constructed 18 of them on the Naviglio di Bereguardo (part of the Milan canal system sponsored by Francesco Sforza) between the years 1452 and 1458.