To cross a stream, road or valley (exactly where the hold off caused by a flight of locks at both side would be unacceptable) the valley is often spanned by a navigable aqueduct – a famed case in point in Wales could be the Pontcysyllte Aqueduct (now a UNESCO https://israelgptzf.ivasdesign.com/58322574/the-definitive-guide-to-canal-infantil