So far you have had to take my word for it that the water in the canals is flowing. Most of the time it isn’t easy to see, as it is not particularly fast and the canal channel is relatively smooth and deep so you don’t get the ripples that you might see in a river. Instead you have to look for debris, sitting in the current, steadily making its way along the canal.
Until you get to a lock…
At a lock the canal level changes in height; not as a slope but as a step. For a boat to descend the step, the lock is filled with water so the boat can enter. Once the gate is closed, the water is drained out until the level falls to the level of the lower canal and the lower gate can be opened. So water moves from the upper level to the lower level, with the boat.
But to get a boat from the lower level to the upper level still results in water moving down the step. With the water in the lock at the lower level, a boat can enter and close the gate but to get the boat to the upper level water has to be added to the lock and this can only come from the upper part of the canal.
Once the water is in the lock, the only way out is into the lower part of the canal, either taking a boat down or just being drained out to let another boat in at the bottom.
So that’s the reason for the flow in the canal – to keep the locks supplied with water.
And there’s more than enough water, with quite a torrent passing down the by-pass chute as well as seepage through the lock gates.