Surface Attractor

Hello everyone, 

I am currently working on a surface( created by a loft tru many curves) ...

i am facing different problems, how can in control the section of the loft at the edge of the surface ? I've tried using sweep 2 rail but i cannot join all of the sweeps to one single surface accordingly. 

i am also trying to develop an attractor on the surface in order to create a defined geometry, either a polygon, ellipse or circle on the surface, trim it, and project it as a continuos surface into the ground. I would like to attract the points of the surface inside the geometry in order for them to go down. 

i have no clue how to continue ... ive tried many things and none seem to work how i want. 

Please help !