To cross a stream, street or valley (the place the delay due to a flight of locks at both side would be unacceptable) the valley is often spanned by a navigable aqueduct – a famous case in point in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Planet https://griffinxhmrv.jts-blog.com/36022168/considerations-to-know-about-urso-fofo