Canal pound

A canal pound is the stretch of level water impounded between two canal locks. Canal pounds can vary in length from the non-existent, where two or more immediately adjacent locks form a lock staircase, to many miles.

History

Pounds came into being with the development of Pound locks to replace the earlier flash locks. A key feature of pound locks was that the intervening level between locks remained largely constant, as opposed to the varible levels created by the opening of flash locks.

Types of pound

Pounds can be described in various ways according to their situation;

ummit pound

A summit pound is formed at a summit on the canal, and where all the defining locks descend from the pound. Summit pounds are particularly important in canal design, as every boat entering or leaving the pound causes a loss of water. Summit pounds therefore need an independent form of water supply, which may take the form of weirs on adjacent rivers, reservoirs or pumping stations. Common practice during canal design was to make summit pounds as large as practically possible, in order that losing a lockful of water would not lower the water level too significantly. The Rochdale Canal is a good example of a canal with a relatively short summit pound, which requires restrictions on lock workings at certain times.

ump pound

The inverse of a summit pound is a sump pound. In contrast to a summit pound, a sump pound is a point where every boat entering or leaving the pound causes an addition of water.

Lock pound

A pound which lies between two locks which lie only a short distance apart. Water levels in the pound are liable to fluctuate as the locks are used.

ide pound

(without the "u").

See also

*Mill race