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Behind the Scenes
How a Lock Works

A lock is a fascinating piece of engineering that allows boats to travel either uphill or downhill. Many rivers posed navigation problems for early river travelers. Locks were the solution that made these waters navigable.

Most rivers have rapids, shallow rocky areas with fast flowing water. In the early history of Canadian exploration, boats that could be lifted out of the water and carried (such as canoes) were used. To go around a rapid, you pulled your boat out of the water and lugged it around. Later, on more traveled waterways, steel pins were put into rock outcrops along the rapids and boats would winch themselves upstream. These boats had to have a shallow draft (didn't sink too deep in the water), and winching was a slow process.

On rivers that were deemed to be necessary for navigation, a more permanent solution was to build a canal around the rapids. A canal is a manmade waterway with a minimum depth of water in it. On the Rideau for instance, the minimum depth is 1.5 metres (5 feet). However if you just dig a ditch to the required depth and let the water flow through it you still have the other problem a rapid has, fast flowing water. In England, such canals were built, and boats were towed upstream by horses or oxen walking along trails built along the side of the canal just for this purpose.

For systems like the Rideau, canals with fast flowing water would not be practical. The solution to slowing down water flow is to build locks. A lock in a canal is essentially a dam, and it keeps the water at the top and bottom from flowing too fast. To get the boat up or down the required elevation it floats the boat in a tub of water. No power is required for a lock, to get a boat up, water is let into the "tub" from the upstream (high water) side. To get a boat down, water is simply let out of the "tub" until the boat is lowered to the level of the water on the downstream (low water) side. The following graphic illustrates the process (my thanks to Koos Fernout of the Netherlands for supplying me with this graphic - it replaces a much cruder version I created a couple of years ago):

Animated Locking Through Sequence

In our example a the boat is "locking down":
  1. A boat comes to the top of the lock and wants to go to the downstream side.
  2. The gates on the upstream side of the lock can easily be swung open because the water inside the lock is the same elevation as the water on the downstream side. So the lock staff turn the cranks that open the gates to let the boat in.
  3. The boat floats into the lock
  4. Now the upper gate is closed.
  5. Valves are opened on the downstream side of the lock which lets water out of the lock.
  6. As the water drains, the boat floats down.
  7. When the water in the lock matches the water level of the downstream water, the gates can be opened and the boat can move out.
"Locking up" is a similar process except that now valves on the upstream side of the lock are used to let water into the lock until the water is the same level as the upstream side.

Animated Lock

Now that you know what a lock does, have a look at The Basics of a Rideau Lock for more detailed information about how a lock is built and how it works.


This is a simple 2 page brochure detailing how a lock works and some interesting facts about locks and the Rideau Canal:

How A Lock Works (English)
Comment fonctionne une écluse (française)


The following is a link to an external website where you can control a locking through:

Comments: send me email: Ken Watson

©1996- Ken W. Watson