To cross a stream, street or valley (wherever the delay because of a flight of locks at either aspect could be unacceptable) the valley could be spanned by a navigable aqueduct – a renowned example in Wales will be the Pontcysyllte Aqueduct (now a UNESCO Entire world Heritage Web-site) https://canalinfantil22109.therainblog.com/35929481/what-does-canal-infantil-mean