To cross a stream, street or valley (the place the delay a result of a flight of locks at either aspect can be unacceptable) the valley may be spanned by a navigable aqueduct – a renowned instance in Wales may be the Pontcysyllte Aqueduct (now a UNESCO Earth Heritage https://rylanyhmrt.tblogz.com/the-best-side-of-urso-fofo-50433678