Use in river navigation Lock (water navigation)

locks on rideau canal, entrance valley, near parliament hill, ottawa canada

when stretch of river made navigable, lock required bypass obstruction such rapid, dam, or mill weir – because of change in river level across obstacle.

in large scale river navigation improvements, weirs , locks used together. weir increase depth of shallow stretch, , required lock either built in gap in weir, or @ downstream end of artificial cut bypasses weir , perhaps shallow stretch of river below it. river improved these means called waterway or river navigation (see example calder , hebble navigation).

sometimes river made entirely non-tidal constructing sea lock directly estuary.

in more advanced river navigations, more locks required.

where longer cut bypasses circuitous stretch of river, upstream end of cut protected flood lock.
the longer cut, greater difference in river level between start , end of cut, long cut need additional locks along length. @ point, cut is, in effect, canal.