lock

Travelling downstream, a boat enters the lock with the lower gates closed. The upper gates are then shut and the water level lowered by draining through sluices. When the water level in the lock reaches the downstream level, the lower gates are opened.

Construction installed in waterways to allow boats or ships to travel from one level to another. The earliest form, the flash lock, was first seen in the East in 1st-century-AD China and in the West in 11th-century Holland. By this method barriers temporarily dammed a river and when removed allowed the flash flood to propel the waiting boat through or over any obstacle. This was followed in 12th-century China and 14th-century Holland by the pound lock. In this system the lock has gates at each end. Boats enter through one gate when the levels are the same both outside and inside. Water is then allowed in (or out of) the lock until the level rises (or falls) to the new level outside the other gate.

Locks are important to shipping where canals link oceans of differing levels, such as the Panama Canal, or where falls or rapids are replaced by these adjustable water ‘steps’.

In a 4 km/2.5 mi stretch of the Worcester and Birmingham Canal at Tardebigge, Worcestershire, England, there are 36 locks that drop the canal nearly 79 m/260 ft.