I'm not entirely sure of its purpose. But there is a little reservoir of water behind that fence, and there might be some mechanical stuff they don't want seen. Otherwise I don't know. Tokyo doesn't have this fence, though they also don't have the mill either. That lift goes up through a cavern instead. With a small house and rockwork on the side where the fence would have been. Disneyland doesn't have the fence either, though is also a different ride system than the others.
I'd advocate just removing the fence outright if it's possible to do. It never looked particularly "good" to begin with, but it looks even worse and stands out like a sore thumb with that mural.