To cross a stream, road or valley (in which the hold off attributable to a flight of locks at both facet can be unacceptable) the valley is often spanned by a navigable aqueduct – a well known illustration in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Entire https://urso-fofo78876.blogars.com/35903772/canal-infantil-for-dummies