How locks on canals work

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From comments on my recent posts, I gather my talk about ‘locks’ has confused some people so I’ll tell you about the locks now. In years gone by, rivers were used to move goods and people up- and down-stream. Canals were built for similar reasons, including to shorten the route between two places but there needed to be a way to travel across land that was not level. A lock is a chamber in which the water level can be varied. These types of locks are called ‘pound locks’ and were first used in medieval China during the Song Dynasty (960-1279 AD). Gates at each end seal off the chamber. Water is let into or out of the lock as required. So, if our boat from going from low-lying land and needed to be raised to the level of the next stretch of water, we would sail into the lock. The gates behind us would be shut and water from the higher leel would be allowed into the lock. Our boat would float up with the water until we were at the same level as the higher water. The gates in front were then opened and we would sail on at our new, higher level. Some of the locks were long enough to take two or three boats. In the left-hand photo, you can see the two levels of water with a road running across the canal above the gates. Our boat needs to be brought up to the level of the ‘high’ water. In the second photo, you can see that the gates are opening and our boat will soon move out into the canal proper. There is also a truck on the road. The photos are a bit deceiving as the walls of the canal look to be a similar depth.