To cross a stream, highway or valley (wherever the hold off due to a flight of locks at either side could well be unacceptable) the valley is usually spanned by a navigable aqueduct – a well known illustration in Wales would be the Pontcysyllte Aqueduct (now a UNESCO Globe https://musica-infantil12221.laowaiblog.com/36029937/musica-infantil-for-dummies