Me and Jakey are of the mind that ~.5' over the dam makes for another 7" --- or so. But I don't think it's a linear construct at all. Even counting for variable input from the tribs I don't think it's linear in terms of lake level over the dam and resulting inches downstream. Also, I haven't kept track of previous anecdotes in my head very well on this. Because of the tribs dumping in the 100.7' on Friday night put the Narrows at 22" if I recall correctly.