To cross a stream, road or valley (the place the delay brought on by a flight of locks at either facet would be unacceptable) the valley can be spanned by a navigable aqueduct – a famed illustration in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Planet Heritage https://urso-fofo80109.pointblog.net/helping-the-others-realize-the-advantages-of-urso-fofo-83887542