<P> At their simplest, canals consist of a trench filled with water . Depending on the stratum the canal passes through, it may be necessary to line the cut with some form of watertight material such as clay or concrete . When this is done with clay, it is known as puddling . </P> <P> Canals need to be level, and while small irregularities in the lie of the land can be dealt with through cuttings and embankments, for larger deviations other approaches have been adopted . The most common is the pound lock, which consists of a chamber within which the water level can be raised or lowered connecting either two pieces of canal at a different level or the canal with a river or the sea . When there is a hill to be climbed, flights of many locks in short succession may be used . </P> <P> Prior to the development of the pound lock in 984 AD in China by Chhaio Wei - Yo and later in Europe in the 15th century, either flash locks consisting of a single gate were used or ramps, sometimes equipped with rollers, were used to change the level . Flash locks were only practical where there was plenty of water available . </P> <P> Locks use a lot of water, so builders have adopted other approaches for situations where little water is available . These include boat lifts, such as the Falkirk Wheel, which use a caisson of water in which boats float while being moved between two levels; and inclined planes where a caisson is hauled up a steep railway . </P>

What effect did canals have in 18th century england