Question

Why aren't canal locks nearly impossible to open?

Answer 1

Because when they get closed a sort of interlocking is formed due to which it is very hard to open them

Answer 2

Lock built in places where the level of the water in the river of canal suddenly change this may be because there is a waterfall there or because the demo area has been built or because there is some other things in the way the lock is like a brick chamber with Gates at each end