Hey Rowly, well if that "saucer bowl" is lined with clay and you figure you have extra height all the way around, I don't see why you couldn't try raising the outflow a foot or two. Just try to keep a couple of feet from the point it will overflow in areas other then the spillway if you can. (I would definitely recomend a spillway still exist even after raising the water line... just to be safe)

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