Fluent Open Channel Simulation
 

I have a simulation that includes a culvert issuing water into one end of an open channel. The inflow boundary has only water. The outflow boundary has a pressure-outlet boundary condition with the free-surface level prescribed. My simulation keeps crashing. The domain fills completely with water, even through I initialize the open channel area to have water on the bottom and air on the top. For some reason, the free-surface level at the outflow does not seem to be controlling anything. Does anyone have any suggestions of what I might be doing wrong?