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 Page 1: Introduction & use of locks
 On navigable waterways, a lock is a particular type of device for raising or lowering boats between stretches of water at different levels. The distinguishing feature of a lock is a fixed chamber whose water level can be varied; whereas in a boat lift or inclined plane, it is the chamber itself which moves.
Locks are used to make a river more easily navigable, or to allow a canal to cross country that is not level.
Use of locks in river navigations
A lock is required when a stretch of river is made navigable by bypassing an obstruction such as a rapid, dam, or mill weir - because of the change in river level across the obstacle.
In large scale river navigation improvements, weirs and locks are used together. A weir will increase the depth of a shallow stretch, and the required lock will either be built in a gap in the weir, or at the downstream end of an artificial cut which bypasses the weir and perhaps a shallow stretch of river below it. A river improved by these means is often called a Waterway or River Navigation.
The lowest lock on a navigable river separates the tidal and non-tidal stretches. Sometimes a river is made entirely non-tidal by constructing a Sea Lock directly into the estuary.
In more advanced river navigations, more locks are required.
- Where a longer cut bypasses a circuitous stretch of river, the upstream end of the cut will often be protected by a a flood lock.
- The longer the cut, the greater the difference in river level between start and end of the cut, so that a very long cut will need additional locks along its length. At this point, the cut is, in effect, a canal.
Use of locks in canals
Early completely artificial canals, across fairly flat countryside, would get round a small hill or depression by simply detouring (contouring) around it. As engineers became more ambitious in the types of country they felt they could overcome, locks became essential to effect the necessary changes in water level without detours that would be completely uneconomic both in building costs and journey time. Later still, as construction techniques improved, engineers became more willing to barge(!) directly through and across obstacles by constructing long tunnels, cuttings, aqueduct or embankments, or to construct even more technical devices such as inclined plances or boat lifts. However, locks continued to be built to supplement these solutions, and are an essential part of even the most modern navigable waterways.
Page 1 - Introduction & use of locks (Current page)
Page 2 - Basic construction and operation...Go
Page 3 - Details & Terminology...Go
Page 4 - Variations...Go
Page 5 - Illustrations...Go
Page 6 - History & Development...Go
Page 7 - Use of water...Go
Page 8 - Alternatives...Go
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