Most that go through the city centre are pretty deep IIRC. The one out the back of my flats were.
Rochdale Canal | Canal & River Trust
This one in fact. You can see where it comes from the ship canal, goes through the city and out towards Rochdale etc.
Lots of locks on that though. Sure city centre ones were shallower as generally they had to be dug out and lined and they never dug out more than they needed. I could be talking utter guff mind.