To cross a stream, road or valley (in which the delay attributable to a flight of locks at either side could well be unacceptable) the valley is often spanned by a navigable aqueduct – a well known instance in Wales could be the Pontcysyllte Aqueduct (now a UNESCO Globe https://canalinfantil55570.free-blogz.com/84344076/canal-infantil-for-dummies