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 may be spanned by a navigable aqueduct – a well-known example in Wales will be the Pontcysyllte Aqueduct (now a UNESCO World Heritage https://canalinfantil78876.blogmazing.com/36136148/a-secret-weapon-for-musica-infantil