Help with attractor points!

Hello!

For starters, I'm a newbie in grasshopper. 

I am trying to create the condition below, where certain parts of a flat surface touch the ground in a smooth way. The image shows exactly what I need, however the surface I have is a planar curved surface (blue surface) as the second image. The points that would touch the ground are in red circles (plan view)

Would greatly appreciate if someone could help me out with this!

Thanks you!