To cross a stream, street or valley (in which the delay caused by a flight of locks at possibly facet can be unacceptable) the valley could be spanned by a navigable aqueduct – a well-known example in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Environment Heritage Internet https://canal-infantil68876.blogsidea.com/43668649/helping-the-others-realize-the-advantages-of-urso-fofo