Lock

The ancestor of the modern lock is the flash lock, also called a navigation weir or stanch. It originated in China and is believed to have been used as early as 50 B.C. The flash lock was a navigable gap in a masonry dam or weir that could be opened or closed by a single wooden gate. Opening the gate or sluice very quickly would release a sudden surge of water that was supposed to assist a vessel downstream through shallow water. This was often very dangerous. Using the flash lock to go upstream was usually safe but extremely slow since the gap in the dam was used to winch or drag a vessel through.

At some point, what now seems to be a very obvious improvement was made, and a second gate was added to the flash lock, thus giving birth to the pound lock. The first known example of a pound lock (whose dual gates "impound" or capture the water) is in China in 984 A.D. Supposedly built by Chiao Wei-Yo on the West River section of the Grand Canal near Huai-yin, it consisted of two flash locks about 250 ft (76.2 m) apart. By raising or lowering guillotine gates at each end, water was captured or released. The space between the two gates thus acted as an equalizing chamber that elevated or lowered a vessel to meet the next water level. This new method was entirely controllable and had none of the hazards and surges of the old flash lock.

Although a primitive form of lock was used in Belgium as early as 1180, the first pound lock in Europe was built at Vreeswijk, Holland in 1373. Like its Chinese ancestor, it also had guillotine or up-and-down gates. The pound lock system spread quickly throughout Europe during the next century and was eventually replaced by an improved system that formed the basis of the modern lock system. During the fifteenth century, the multi-talented Italian artist, Leonardo da Vinci (1452-1519), served the Duke of Milan as engineer and devised an improved form of pound lock whose gates formed a V-shape when closed. In 1487, da Vinci built six locks with gates of this type. These gates turned on hinges, like doors, and when closed they formed a vee shape pointing upstream-thus giving them their name of miter gates. Da Vinci realized that one great advantage of miter gates is that they were self-sealing by the pressure of the water (since they point upstream). Also when there is a difference in water level between one side and the other, the pressure holding the gates together is at its greatest. Most of the great canals of Europe use locks. In France, the Briare Canal, completed in 1642, included 40 locks, one series of which was a staircase of six locks that handled a fall of 65 ft (20 m). The famous Canal du Midi that leads to the Mediterranean was finished in 1692 and used 26 locks to surmount the 206-ft (61 m) difference from Garonne to Toulouse. It then descended 620 ft (189 m) through 74 locks. The first lock in England was built in 1566, but it was not until 1783 that a lock was completed in North America at Lake St. Francis in Canada.