To cross a stream, highway or valley (wherever the hold off a result of a flight of locks at both side could be unacceptable) the valley can be spanned by a navigable aqueduct – a famed example in Wales is definitely the Pontcysyllte Aqueduct (now a UNESCO Earth Heritage https://myleswwwse.iyublog.com/36145934/indicators-on-canal-infantil-you-should-know