To cross a stream, highway or valley (where the hold off caused by a flight of locks at either facet could well be unacceptable) the valley is usually spanned by a navigable aqueduct – a well-known example in Wales is the Pontcysyllte Aqueduct (now a UNESCO World Heritage Site) https://canal-infantil99876.dbblog.net/10326257/rumored-buzz-on-canal-infantil