To cross a stream, road or valley (wherever the hold off brought on by a flight of locks at both facet might be unacceptable) the valley can be spanned by a navigable aqueduct – a renowned instance in Wales may be the Pontcysyllte Aqueduct (now a UNESCO Globe Heritage https://urso-fofo91100.boyblogguide.com/36051277/canal-infantil-an-overview