To cross a stream, street or valley (where by the hold off a result of a flight of locks at either side can be unacceptable) the valley may be spanned by a navigable aqueduct – a famous illustration in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Entire https://musica-infantil23322.blogocial.com/helping-the-others-realize-the-advantages-of-urso-fofo-72872736