To cross a stream, street or valley (the place the delay brought on by a flight of locks at both side would be unacceptable) the valley can be spanned by a navigable aqueduct – a famed case in point in Wales could be the Pontcysyllte Aqueduct (now a UNESCO https://canalinfantil04703.blogoscience.com/43583905/musica-infantil-for-dummies