That is cool. I had never heard of that Island. It reminds me of something here in Tucson. They are scaled swales and they were man made dams in a horse shoe pattern to sort of trap the water there from little washes.
I have been back there before and the whole area was lush grass with trees around the rim. It was like walking into a totally different ecological environment. I tried to plant watermelon out there and some other stuff but the plan of having a huge feast didn't pan out. Hahahha