Circle Packing and Attractor Curve

Hello! 

I am trying to create a definition that will set out a paver plan along a river where the pavers are close together at the level of the water and move father apart as they get away from the water. I have been successful using a box as the geometry, but I would like to use packed circles. I have included a screenshot of the definition and what I have so far. Any input would be greatly appreciated. 

Thank you.