To cross a stream, highway or valley (where by the hold off due to a flight of locks at both side would be unacceptable) the valley can be spanned by a navigable aqueduct – a famed illustration in Wales may be the Pontcysyllte Aqueduct (now a UNESCO World Heritage https://elliottqafim.blogstival.com/58685340/indicators-on-canal-infantil-you-should-know