To cross a stream, road or valley (exactly where the delay caused by a flight of locks at possibly side might be unacceptable) the valley can be spanned by a navigable aqueduct – a renowned illustration in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Planet Heritage Web https://cesarpvycg.full-design.com/considerations-to-know-about-urso-fofo-79499873