Why do leaves group at the edges of a pool?

[katiecat486]

What causes objects (such as leaves) in the pool to group at the edges?

 

[mgb_phys]

The wet leaves stick to the sides of the pool.
It's called a "constrained boundary random walk" the leaves drift randomly over the surface, blown by wind + ripples but when the touch the side they stick. So statstically eventually all will end up on the edge of the pool.

 

[katiecat486]

Thanks!