To cross a stream, highway or valley (exactly where the delay because of a flight of locks at either facet might be unacceptable) the valley is usually spanned by a navigable aqueduct – a well known instance in Wales is the Pontcysyllte Aqueduct (now a UNESCO Earth Heritage Website) https://musica-infantil76554.ampblogs.com/the-smart-trick-of-musica-infantil-that-no-one-is-discussing-73825416