The canal lock is a simple yet highly effective device that solves the problem of how to get boats to go uphill on rivers and artificial waterways. Navigation on rivers is possible for many miles when the river is slow-moving and only dropping by a small amount as it moves towards the sea, but when the gradient increases and the water flows faster, it becomes impossible for vessels to proceed. Likewise, canals cannot always be level – they have to go up and down hill in order to get from A to B if the places in question are at different heights above sea level or there is a hill that gets in the way.
China had an extensive canal system in ancient times – back as far the “BC” years – but the gradient problem was avoided rather than tackled. When a lock was required, it took the form of a barrier against which the water was allowed to build up. When the barrier was raised the water rushed down and took any boats with it. However, this was not very useful for boats that wanted to go upstream, as they would have to be carried round the barriers or their cargoes unloaded and carried round to another boat that was waiting on the other side.
In 983 AD an engineer called Chiao Wei-Yo had the idea of placing two barriers a short distance apart and creating a pound of placid water between the two which could be filled and emptied under complete control. Although the water could only ever flow in one direction, a boat could proceed upstream just as easily as downstream by riding on the rising or falling water in the pound.
The idea was re-invented in Europe in the fourteenth century, with the first “pound lock” being built at Vreeswijk in Holland in 1373.
However, one problem with early locks was that they relied on gates being lowered and raised into and out of the water. This meant that only boats below a certain height could use them. The problem was solved in the 16th century with the invention of the “mitre gate”, which is a double gate that closes to form a V shape pointing upstream, such that the pressure of water keeps it firmly closed. Water is allowed into the lock via sluices in the gate (or via channels around the gate in many modern locks) until the height in the lock is the same as that outside, at which point the gates can be swung open to admit or release a boat.
The beauty of this design is that thousands of gallons of water can be moved through a lock, together with boats weighing many tons, without any power being needed other than that of the water itself and the physical strength of the boat owner to open and close the gates and operate the sluices. As with most processes, there are ways of getting it wrong as well as right, but most canal users get the hang of operating locks very quickly and with only the minimum amount of instruction being needed.
China had an extensive canal system in ancient times – back as far the “BC” years – but the gradient problem was avoided rather than tackled. When a lock was required, it took the form of a barrier against which the water was allowed to build up. When the barrier was raised the water rushed down and took any boats with it. However, this was not very useful for boats that wanted to go upstream, as they would have to be carried round the barriers or their cargoes unloaded and carried round to another boat that was waiting on the other side.
In 983 AD an engineer called Chiao Wei-Yo had the idea of placing two barriers a short distance apart and creating a pound of placid water between the two which could be filled and emptied under complete control. Although the water could only ever flow in one direction, a boat could proceed upstream just as easily as downstream by riding on the rising or falling water in the pound.
The idea was re-invented in Europe in the fourteenth century, with the first “pound lock” being built at Vreeswijk in Holland in 1373.
However, one problem with early locks was that they relied on gates being lowered and raised into and out of the water. This meant that only boats below a certain height could use them. The problem was solved in the 16th century with the invention of the “mitre gate”, which is a double gate that closes to form a V shape pointing upstream, such that the pressure of water keeps it firmly closed. Water is allowed into the lock via sluices in the gate (or via channels around the gate in many modern locks) until the height in the lock is the same as that outside, at which point the gates can be swung open to admit or release a boat.
The beauty of this design is that thousands of gallons of water can be moved through a lock, together with boats weighing many tons, without any power being needed other than that of the water itself and the physical strength of the boat owner to open and close the gates and operate the sluices. As with most processes, there are ways of getting it wrong as well as right, but most canal users get the hang of operating locks very quickly and with only the minimum amount of instruction being needed.
© John Welford
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