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Construction And Operation

The earliest locks were built entirely of wood, with stone and then brick becoming standard materials. The gates themselves were always wooden, with some lasting as long as 50 years. Filling or emptying these early locks was often accomplished by hand-operated sluices built in the gates. On later and larger locks, it was found that conduits or culverts built into the lock wall itself were not only more efficient but let the water enter in a smoother, more controlled manner. Nearly all locks operate in the following manner: (1) A vessel going downstream to shallower water enters a lock with the front gate closed. (2) The rear gate is then closed and the water level in the lock is lowered by opening a valve. The vessel goes down as the water escapes. (3) When the water level inside the lock is as low as that downstream, the front gate is opened and the vessel continues on its way. To go upstream, the process is reversed, with the water level being raised inside the lock. What the operators always strive for is to fill or empty the lock in the fastest time possible with a minimum of turbulence. In modern locks, concrete and steel have replaced wood and brick, and hydraulic power or electricity is used to open and close the gates and side sluices. Movable gates are the most important part of a lock, and they must be strong enough to withstand the water pressure arising from the often great difference in water levels. They are mostly a variation of da Vinci's miter gates, except now they usually are designed to be stored inside the lock's wall recesses.

Probably the best known locks in the world are those used in the Panama Canal—the most-used canal in the world. Completed in 1914, the Panama Canal is an interoceanic waterway 51 mi (82 km) long that connects the Atlantic and Pacific Oceans through the Isthmus of Panama. It has three major sets of locks, each of which is built in tandem to allow vessels to move in either direction, like a separated, two-way street. Each lock gate has two leaves, 65 ft (20 m) wide by 7 ft (2 m) thick, set on hinges. The gates range in height from 47-82 ft (14-25 m), and are powered by large motors built in the lock walls. The chambers are 1,000 ft (305 m) long, 110 ft (33.6 m) wide, and 41 ft (12.5 m) deep. Most large vessels are towed through the locks. As with all locks today, they are operated from a control tower and use visual signals and radio communications. Any future major changes or improvements in the canal or its locks must consider the fact that ocean-going vessels are simply becoming too large to pass through. The future may see the construction of a sea-level canal 10 mi (16 km) west of the existing canal. If so, it, like the Suez Canal, will contain no locks of any kind.



De Bono, Edward. Eureka! An Illustrated History of Inventions From the Wheel to the Computer. London: Thames and Hudson, 1974.

Paget-Tomlinson, Edward. The Illustrated History of Canal & River Navigations. Sheffield, England: Sheffield Academic Press, 1993.

Leonard C. Bruno


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Flash lock

—A simple wooden gate that was placed across a moving body of water to hold it back until it had become deep; the sudden withdrawal of which would cause a "flash" of water downstream that would carry a boat over the shallows below.

Guillotine gate

—An early wooden gate on a lock that was operated by being raised or lowered.

Miter gate

—An improved type of lock gate that turns on hinges, like a door, and meets to form a vee pointing upstream.

Pound lock

—A name for an early form of two-gate lock in which a chamber is enclosed at either end by vertically-rising gates and into which water is admitted or released to change its water level and allow a vessel to do the same.

Staircase lock

—Two or more locks sharing a common gate that form a series of water steps and allow a vessel to negotiate a steep rise.

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