How thick are the rings of Saturn and Uranus?

Uranus' outermost and most massive ring, called the Epsilon Ring, is only about 100 kilometers wide and probably less than 100 meters thick. The other ten dark and narrow rings have a combined mass less than the Epsilon Ring. The six rings of Neptune are less significant than Uranus' and the ring particles are not uniformily distributed in the rings. Like Saturn's F ring, the rings of Uranus and Neptune are kept narrow by shepherd satellites. The narrowness and even clumpiness of the rings means that the rings can last for only a short time---a million years or so, unless the rings are replenished by material ejected off the moons in large collisions.