To cross a stream, street or valley (in which the delay attributable to a flight of locks at either facet could well be unacceptable) the valley is often spanned by a navigable aqueduct – a popular illustration in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Planet Heritage https://urso-fofo79997.bloggosite.com/44411740/the-2-minute-rule-for-urso-fofo