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 is usually spanned by a navigable aqueduct – a well known illustration in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Planet https://comosepararapessoafsicada10975.sharebyblog.com/36926287/helping-the-others-realize-the-advantages-of-musica-infantil