To cross a stream, road or valley (exactly where the delay attributable to a flight of locks at both side might be unacceptable) the valley can be spanned by a navigable aqueduct – a famous instance in Wales is definitely the Pontcysyllte Aqueduct (now a UNESCO Environment Heritage Website) https://urso-fofo55543.tribunablog.com/the-best-side-of-urso-fofo-51485772