Lock (water Transport) - Use of Locks in River Navigations

Use of Locks in River Navigations

When a stretch of river is made navigable a lock is required to bypass 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 (see example Calder and Hebble 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 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.