Circular water

So I'm a bit of a sticky situation. I want to use a water block to fill a circular water reservoir structure that is open on the top. From what I can gather about how water blocks and the river editor work in Torque is that they intersect through things like the terrain and are meant to be hidden by it. This can't work here since the tower is circular and sits above the terrain. Is there a way to trim a water block the same way you can trim a terrain block?