Today I made a simple model to show off my waterfall idea.
Tell me what you think JFT and Justin.
Hope you don't mind if I wedge a word or two in sideways, as well...
I must have missed some earlier part of Justin's descriptions, because when I see that picture, I can't stop myself from wondering where the seawater goes, after flooding that little valley. ('similar thoughts about the waterways all along, actually.)
With the earlier talk about pumps and things, the obvious guess was that maybe the "castaway" built all that stuff in order to create the swampland area (ie. it didn't use to be there), probably for agricultural use.
The first thought that maybe makes sense about the seawater basin (already lowest point), is to make the assumption that it is some sort of tidal-cycled hydro powerplant, with waterwheels or turbines at entry and drain points, or a collection device for some sort of seafood which gets trapped in the valley as the tide recedes (now the net at the drain has rotted, though).