Hi, David. Yes, some bivalves can burrow upward through the sediment that has been dumped on top of them. Others can't. The amount differs from species to species, and, I suspect, is also dependent on how exhausted the poor dears are before they start. There is actually a fairly large literature on the subject, and I'd guess that 0.5 m (half a yard) of sediment would be enough to wipe out most of the fauna. But "book knowledge" is nothing like actually being there on the spot before and after a beach replenishment, and I do not have that experience. Apologies to FRED Hinkle for calling him FRANK... We have a Frank Hinkle here on staff, no kidding! Andrew K. Rindsberg Geological Survey of Alabama