Size of the channel, 2. Slope of the channel, and 3. Let's try an example to see if you were right. Now it is your turn. Just change either the lining or the slope or the depth and see if the water velocity changes like you thought.
Water goes faster when the channel is deeper, steeper, and smoother.
Now try an example closer to the real world, like a stream. The water is moving faster than before. Water on the land surface moves much faster than it does underground. Now let's look at the speed of water in the groundwater.