To cross a stream, street or valley (the place the delay brought on by a flight of locks at either facet might be unacceptable) the valley may be spanned by a navigable aqueduct – a well known example in Wales is definitely the Pontcysyllte Aqueduct (now a UNESCO Environment https://raymondtchlo.activosblog.com/35945892/the-smart-trick-of-musica-infantil-that-no-one-is-discussing