Does your proposed pond site have a seasonal crick bed or tile? If not then how much water is flowing through this valley? Is it so much that it could wash out the damn? or would you have an almost constant overflow?

the other possability is that there is a sand vein diverting water into underground storage. My pond is being built on an ex-sand vein, now its a gravel pit. Find out what the price of sand is in your area
(in southern MN its about $.75/yard) that eqauls a lake plus profit. Worst case scenario you build a large pond on site #1 and hold on the the acerage.