To cross a stream, highway or valley (in which the delay because of a flight of locks at possibly side might be unacceptable) the valley is often spanned by a navigable aqueduct – a popular instance in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Earth Heritage Web https://zaneweknq.blogpayz.com/37285362/the-ultimate-guide-to-urso-fofo