To cross a stream, road or valley (where by the hold off a result of a flight of locks at both side would be unacceptable) the valley could be spanned by a navigable aqueduct – a well-known example in Wales is definitely the Pontcysyllte Aqueduct (now a UNESCO Earth https://damienmcknq.dailyhitblog.com/42562668/musica-infantil-for-dummies