sentence: Locks are built in places where the level of the water in the river or canal suddenly changes.
sentences_before: A 'lock' is a place where boats that are travelling up or down a river or canal can be raised higher or lower.
sentences_after: This may be because there is a waterfall there, or because a dam or a weir has been built, or because there is some other thing in the way. The lock is like a big chamber with gates at each end. They have lock gears which empty or fill the chamber with water.
concept_name: lock
headings: Lock (water transport)
categories: Canals Rivers Gates