Making a volume by intersecting faces

Duncan

Hello,

I am trying to mesh a river channel in Fluent. At present I am having problems producing the geometry within Gambit. I have imported vertex which were derived from a digital elevation model. I then manually joined the vertex and then used a skin surface to make a face (a complex surface) which is essentially the river bed and banks. This extends beyond the free surface as i want to simulate a number of flow conditions.

I then imported vertex which described the location of a free surface condition and produced another face. I would now like to Intersect the topography face with the free surface face to leave a control volume for 3d meshing (ie the fluid continuum). However, this seems to be impossible with the complex topography i have.

Does anyone have any pointers or useful tips with how to proceed further?

Many Thanks for any advice,

Duncan