Contours and the use of breaklines

tylcoatc

When generating contours, the results in a river are often not good. I have understood a breakline/s help.
I vaguely understood that a breakline will force the triangulation to look upstream instead of across the river?
If I am on the right track how do I use breaklines in this context???
I would have liked see a worked example.
Found one but it does not include a breakline?