"I think I will keep the ponds on the smaller side partly because I'm not a millionaire and I think a big dam would be expensive."
Depending on the topography of the land, you might pile up 1/10th of the dirt to impound X surface acres of water, compared to excavating the same size of pond in flat terrain. (Lots of dirt work is priced on the cubic yards of dirt moved.)
Of course, it is not that simple - you don't "pile up" dirt to make a dam. You do have to properly construct a core trench which adds to the expense.
However, the principle remains the same for a 4-acre pond or a 0.4 acre pond. Building an embankment pond with a dam located in the narrowest spot between the plateau slopes should be LESS expensive for the acre-feet of impounded water relative to digging out a pond.
