To cross a stream, road or valley (wherever the hold off caused by a flight of locks at possibly facet can be unacceptable) the valley is usually spanned by a navigable aqueduct – a renowned case in point in Wales will be the Pontcysyllte Aqueduct (now a UNESCO Globe https://urso-fofo57765.blog-ezine.com/37377867/a-review-of-canal-infantil