To cross a stream, road or valley (in which the hold off attributable to a flight of locks at possibly side can be unacceptable) the valley can be spanned by a navigable aqueduct – a well-known illustration in Wales is the Pontcysyllte Aqueduct (now a UNESCO Globe Heritage Internet https://cursodoelgato02456.azzablog.com/37403228/canal-infantil-for-dummies