To cross a stream, street or valley (in which the delay attributable to a flight of locks at either aspect could be unacceptable) the valley can be spanned by a navigable aqueduct – a famous case in point in Wales could be the Pontcysyllte Aqueduct (now a UNESCO Entire https://lukasdmswa.affiliatblogger.com/89225076/detailed-notes-on-musica-infantil