I haven't used this software in a long time.
Is there not a way to dig into the terrain anymore???????
Use the Painted Shader: http://www.planetside.co.uk/wiki/index.php?title=Painted_Shader_Guide
Scroll to the bottom for an example of using it for Displacement, which is probably what you want. In your case *negative* displacement.
I give some more specific instructions here as well: http://www.planetside.co.uk/forums/index.php/topic,16857.msg164429.html#msg164429
- Oshyan
Thanks very much I'll give that a shot.