Hi, I am a nub. I've been watching this site as an outsider for a little while now. I find your Turtle city so fun I am inspired to register. See the influence you have over people?!
Anyway, I have a suggestion for you to think about with regard to the fresh water problem. I hope this isn't too late. (It may not be the most politically correct for circa 2014 but it seems to me to be an obvious old school solution.) You have some pretty nice valleys in the center of the island, so with 60 inches of rain per year you also likely have some pretty nice rivers there, too. Why not create a storage reservoir(s)? I can help you size the reservoir to your needs, if you don't already know to do that. The size of the reservoir may influence how large you decide to size the island. It may create some valuable lake-front property. The whole thing would be done at the expense of farmland, if you kept it on the surface, so you would have to consider that. Something to think about.
If you are worried about the weight of so much high-elevation water, you could consider a subterranean reservoir or low level surface one toward the coast. You would have to pump the water or come up with a pressurized infrastructure, depending on your tech level. I personally think you're going to have plenty of buoyancy from that large a turtle and this isn't a concern.
If you are high tech, you could consider hydropower. A city near me (Idaho Falls: 50,000 pop.) supplies all of its power needs to its citizens with one river and a couple of dams.
Super idea! Can't wait to see how it all turns out!! Good luck.
Last edited by GeoPopID; 04-18-2014 at 01:52 PM.
Thanks for the suggestions. Its never to late, especially since this project is on the back burner till I complete a couple of others. Its the reward at end of the stick for myself.