Floating Top Boundary
 

Hi, I have a rectangular-bed channel, for simulating a river channel condition. I want to look at the effect of ice-cover surface on the top of the flow in the channel. However, the ice-cover surface on the top of river, is not fixed to the river banks; it is a floating surface on the top of the water. So, I was wondering how I might be able to simulate the top wall of my channel to be floating in OpenFOAM?

I created my current mesh with 4 fixed walls but in fact need to simulate a floating top wall. Can you let me know if it is possible at all in OpenFOAM to model a floating top wall boundary?
Thank you.
Ebr