To cross a stream, street or valley (in which the delay caused by a flight of locks at possibly side could be unacceptable) the valley may be spanned by a navigable aqueduct – a famous case in point in Wales could be the Pontcysyllte Aqueduct (now a UNESCO Earth https://musica-infantil29371.fireblogz.com/68406206/a-secret-weapon-for-musica-infantil