The fascinating thing about the Munich gravel plain is that it's really just a (very slightly inclined) plain - it's almost 100% flat, and the gravel is covered by a (relatively thin) layer of soil, so you could easily mistake it for the typical "lowlands" alluvial plain, and you'll probably be surprised to learn that it's at a height of ~400-700 m. So you don't really have to worry about the gravel moving - but it's still there...