To cross a stream, highway or valley (the place the delay attributable to a flight of locks at both side would be unacceptable) the valley is usually spanned by a navigable aqueduct – a famed illustration in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Planet Heritage Internet https://martinmwaei.digitollblog.com/36972129/indicators-on-canal-infantil-you-should-know