I am trying to model the flow in pipe.  The conditions need to change once the pipe is full.  I have attempted to model this, but I keep getting a divide by zero once the pipe is full.
I am trying to understand why this is happening.  I have attached the simple model.  When I run TestTrap1 is works for a period of time, then gives divide by zero errors.  If anyone can make any suggestions for getting it to work, I would greatly appreciate it. 
Thanks.
FlowPackageTest.mo