The steep land was covered in swales laid on contour. I saw a man with a hoe re-building them up. These hills were close to a section of the Great Wall, and the curvy road went over hills and through valleys. I wonder if they were to catch sudden rains, or gather the chestnuts when they fell. Sorry I didn't take a picture.
Indigenous intelligence goes back into generations and generations of wisdom. Not to say that PDC principles don't apply, but in a situation like that in China, there have been so many millions of hours of observation that they probably have the amount of water that swale can hold down to a teaspoon.
I wish I had the time to just go to places like that and ask a lot of questions.