To cross a stream, highway or valley (wherever the hold off because of a flight of locks at possibly aspect can be unacceptable) the valley might be spanned by a navigable aqueduct – a renowned case in point in Wales is definitely the Pontcysyllte Aqueduct (now a UNESCO Globe https://urso-fofo79997.bloggosite.com/44411740/the-2-minute-rule-for-urso-fofo