Obtain only the required Surfaces

[s.iwasaki]

Surface and Surface Subtraction

I am looking to subtract Surface from Surface as shown in the diagram. The water surface is one large Surface. The surface representing the terrain is a PolySurface, which is a combination of various Surfaces. How can we subtract the PolySurface representing the topography from the surface representing the water surface to obtain the water surface as shown in the figure? I am assuming this will be done in Dynamo. I would appreciate it if you could lend me your thoughts. [Image]

I was able to cut out the Surfaces that represent water surfaces using the method you taught me. However, there are some surfaces in the list that I need and some that I don’t.
How can I extract only the blue surface that represents the water surface?

[jacob.small]

Transpose the squiggly line down by a slight distance (say polysurface.Transpose(0,0,-0.1). Then check it for intersection with the split surfaces - if they intersect you want to toss them.

[s.iwasaki]

Thanks for the reply.
I was able to get the Surface of the water with this idea.
The image is a simplified model.