To cross a stream, street or valley (exactly where the delay due to a flight of locks at both facet would be unacceptable) the valley is usually spanned by a navigable aqueduct – a famous case in point in Wales is definitely the Pontcysyllte Aqueduct (now a UNESCO Planet https://urso-fofo55421.blogoxo.com/37389629/indicators-on-canal-infantil-you-should-know