I am attaching a topo map of the area around my pond in the hopes that maybe someone with some more expertise could give a rough estimate of runoff area.
I come up with about 5 acres or so...

Construction is nearing completion and the final size looks to be more in the 1.6 acre range.
If runoff is insufficient to keep it fill it I think my next best option may be to pull some water from a stream that is about 200 or so feet away.

Yellow lines represent road (and ditches). Backside of dam is approximately 270-300 feet for scale.

jammer