What is a canal lock?
A canal lock is a structure that connects two stretches of water at different levels using movable gates, so that boats can be raised or lowered between them. The usual form is the pound lock: a chamber with gates at each end. A weir holds water back at a set level; a lock is above all a passage. Related structures that control the flow of water rather than boats are called sluices.
Types of lock and sluice
- Pound lock (chamber lock). Upper and lower gates with the lock chamber between them. Found on canals and river navigations.
- Sea lock. Separates a harbour or canal from tidal water. The IJmuiden sea lock in the Netherlands, opened in 2022, is 500 m long, 70 m wide and 18 m deep.
- Lock flight. A series of locks in quick succession to climb a hill, such as the Caen Hill flight on the Kennet and Avon Canal.
- Sluice. A gate or channel to release or admit water, for example to drain low-lying land or relieve flood water. The Dutch term sluis covers both locks and sluices.
How a lock works
- The boat enters the chamber and the gates behind it are closed.
- Paddles (sluices in or beside the gates) are opened to fill or empty the chamber.
- Once the level matches the water ahead, those gates are opened and the boat moves on.
Gate types
- Mitre gates. Two leaves that meet at an angle pointing upstream; water pressure holds them shut. The most common type.
- Guillotine (vertical lift) gates. Raised vertically.
- Sliding or rolling gates. Move sideways into a recess; used on wide sea locks.
- Sector and flap gates. Rotate on a vertical or horizontal axis.
Application
Locks are operated by the navigation authority, such as the Canal & River Trust on many waterways in England and Wales. Building work near a lock, embankment or watercourse often needs consent from the relevant authority, so check first.
Boaters: follow signals and lock keeper instructions, keep clear of the gates and cill, and tend your lines.
Related terms
- Civil engineering structure
- Pumping station
- Dike monitoring
- Water level management
- Emergency dike
- Storage basin
Want to know more about building terms? Visit our knowledge base at fredsdiyplans.com.