gambit open channel geometry
 

I have read numerous comments on how to set the boundary conditions for open channel flow using VOF. My problem is to create an appropriate geometry in gambit, because following my last experience, only closed volumes can be meshed and I wonder how to create something that is open and mesh its interior.
Please explain how the simplest possible open channel geometry can be created, preferably in 2d.

workaround solution
 

My workaround was to not use the openchannel flow option in VOF and instead using two different velocity inlets, one for phase1 and one for phase2. This seems to work when combined with one pressure outlet. Please note that the geometry is a closed rectangle with inflow on the left and outflow on the right. In the middle there is a small obstacle because I want to study the hydraulic jump for an over critical (Fr>1) flow.:confused: