Ed,
What a difference the location makes...
In my area, for example, annual rainfall is 50 to 60 inches. I built a 4 acre pond with only about 3 acres of watershed and until this recent Texas drought, it stayed spillway full for 4 years. Even now it is down 2-3 feet, which is a managable number.
Where do you get the annual evaporation number from? Presumably it varies by local also.
Location, location, location.
