How to make Bankfull depth equal across entire river length?

Im having a major issue when using the river tool where the rivers bankfull depth is not the same depth across a relatively flat area. The issue is that the river will go up and down in elevation within the same river length. Its a bit difficult to show here, but the rivers flow is going up this little hill here, rendering the river pretty much useless since I need it to be the same depth across the entire terrain.

What can I do?