To cross a stream, street or valley (in which the delay brought on by a flight of locks at both aspect will be unacceptable) the valley may be spanned by a navigable aqueduct – a well-known example in Wales is the Pontcysyllte Aqueduct (now a UNESCO Earth Heritage Web-site) https://lorenzodouyc.thechapblog.com/36168582/rumored-buzz-on-canal-infantil