To cross a stream, street or valley (where the delay attributable to a flight of locks at both facet 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 Web page) https://tysontchlp.blogdiloz.com/35969899/detailed-notes-on-musica-infantil