I followed your instructions and began the simulation. Initially, I set both the "Open Channel Flow" and "Open Channel Wave BC" with a "Velocity Inlet" boundary condition (BC). By doing this, I realized that I might have disregarded the "Open Channel Flow" since it should actually have a "Pressure Inlet" BC. I also tried the reverse setup.
In both configurations, the pressure differential (dP) was minimal and almost identical when I set the upper boundary condition as "Symmetry". I then attempted to change the upper boundary condition to "Pressure Outlet". Interestingly, although the iterations proceeded normally, I encountered a reverse flow error and observed unusual (wrong) velocity contours, as shown below.
I wonder what is the reason of this situation, everything is same just I changed upper BC. dP value is also strange but at least it's big. I believe that if I can solve this problem, I'll start to get logical free surface elevation.
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