Gravel placed on clay bottom without benefit of landscape fabric will integrate into the pond bottom and disappear into muck in a few seasons, just fyi. Just a fact of pond life in NE. I have several 3-6" limestone "fields" in my pond, and after 8 years they are entirely buried in organic material/silt. I receive very little runoff in the pond, also. Just trying to manage your expectations. The large rock [8-12"+] placed deeper is still free of silt and isn't buried nearly as much. Building a beach in a clay pond is somewhat of an undertaking, several posts on forum discussing the process. Bottom line, it's not as easy as we'd like it to be. If you want gravel/rock to remain separate form pond bottom in NE one needs to elevate it, use larger rock, or employ landscape fabric.