To cross a stream, road or valley (exactly where the delay brought on by a flight of locks at possibly aspect would be unacceptable) the valley may be spanned by a navigable aqueduct – a well known example in Wales is the Pontcysyllte Aqueduct (now a UNESCO Globe Heritage https://urso-fofo67765.blogtov.com/17655354/urso-fofo-can-be-fun-for-anyone