To cross a stream, street or valley (in which the delay caused by a flight of locks at both aspect will be unacceptable) the valley could be spanned by a navigable aqueduct – a well known example in Wales is the Pontcysyllte Aqueduct (now a UNESCO Environment Heritage Internet https://musica-infantil66543.blogdomago.com/35921393/the-single-best-strategy-to-use-for-musica-infantil