"Rob & Shel" wrote in message

However the gully water was really flowing quite fast into the dam
dragging
loose leaf litter & small sticks etc. I figure this gully needs
small
filtering walls of rocks.

That'd work or old tyres. Old tryes will slow the flow and can be
planted out as they silt up with useful plants. I woulnd't really
recommend bulrushes on the top side of the dam as these sodding
things take over.