Volume source rate
 

Hi,
I have a simple plot setting with sloping surface for Shallow water modeling. The 4 faces (x-min, x-max, y-min, z-min) are set wall boundary and upper (z-max) is set pressure boundary and y-max is set outflow boundary. I want to apply volume source rate uniformly (rainfall) only to open upper boundary. But it seems FLOW-3D accounts outflow boundary into open boundary too. How can I apply volume source rate uniformly only to upper boundary which is sloping surface?
Thank you,