Nice number crunching lmoore!
...Another question I have. The pond tapers from shallow at the input creek to about 9' deep across the back where the drainpipe is, with the exception of a hole near the back corner that goes to 16' deep. Would it be better to put the diffuser in the shallower water near the input creek, or in the deep hole?
It depends on a number of things, but simply put...you get the best water turnover with a deeper setting of the diffuser. That is, if your pump can pump to that depth with an appropriate amount of air volume.
A 1 acre pond with about 2 million gallons of water will turn over once in a day with only one diffuser at a depth of 10 feet. If I were setting only one diffuser in that pond, I'd put it in, or close to, the 16 foot hole and gain more turnovers in a day, once in 14 hours, thereabouts. This assumes you can build the pressure (~9 psi depending) and maintain the 1-2 CFM requirement of the diffuser.
The only thing that would change my mind would be if the incoming spring water was low in DO. Then I would have to think about what location would best suit the single diffuser. That's were the DO testing would come in handy. If you found a low DO area on a particular side of the pond, I'd move the diffuser closer to that spot, given that is a consistent low DO area and does not move around on you. If that would be the case...I'm back to putting it in the deepest hole or, at least, near it on the shallow side of the deepest spot.
Keep in mind that I have only thrown out my thoughts for a single diffuser system. A 1 acre pond would do better with a couple more spread out from each other. On paper, the lift rate numbers crunch fine for a single diffuser, but I cannot comment on how much of the water surrounding that one diffuser gets recirculated top to bottom again and again leaving waters further away mostly untouched. Adding diffusers requires more CFM, obviously...so, you may be limited to what the contraption can supply.
