The 3 foot diameter drain pipe lead me to think the pond had a real heavy throughput. That's a huge pipe for a 1 acre pond, but the average flow you are stating is not so heavy for that size of pipe . At 1 gallon per second , equivalent to 60 GPM, and assuming your 1 acre pond has about 2 million gallons...the turn over rate for completely exchanging the pond's water contents, simply, is about once every 23 days. Probably longer since it is not and exact put-and-take situation. That sounds like aeration would be much more efficient than I originally thought while assuming a heavy throughput.

With any throughput flow and aeration of any type, the aerated water will flow out of the pond (Imagine dying the pond - within 23 days, thereabouts, almost all of the dye will be gone) The higher the flow the less good your system will be doing and the larger the system would need to be to compensate for the loss of aerated water, but at 60 GPM, I suspect the standard size system would be fine. Putting a diffuser in the drain pipe confuses me with respect to what you were thinking. You might as well put it in your bathtub compared to in the drain pipe...lol. The best place for most of the diffusers would be where the water comes into the pond (assuming low DO in the spring water)...aerate it as soon as it enters the pond, giving the aerated water as much time in the pond as possible before exiting through the drain pipe.

If is was contemplating aerating this pond, I would buy a DO test kit and test the water coming in the pond, out in the middle, & near the drain pipe. At the deeper areas (middle and near the drain), sample water from about 12 inches below the surface. The "CHEMetrics K-7512 Dissolved Oxygen Kit" is as affordable (60-$70) and reliable as you can get without spending hundreds of dollars. It comes with enough "stuff" to do 30 tests. If your DO levels are good, I would concentrate on making your contraption do something to beautify the pond rather than aerate. Unless. of course, you are trying to maximize the fish capacity and attack th ebottom muck of the pond, then aeration would be key.

As far as a water wheel goes, I am interested in what you mean by "1200 Foot-Ponds per Minute". I do not recall seeing torque expressed with a factor of time. In my mind, you would need to know how much torque (foot-pounds or inch pounds) it takes to turn the wind mill pump to make sure the water mill can produce that torque. This will likely be a variable with the output CFM's of the pump, so you would be looking for a curve with torque on one axis and CFM on the other axis. As little as "3-5 mph winds" means the pump is producing very little air production compared to much higher wind speeds.

The next trick would be estimating how big the water mill would need to be and the gearing to the pump (or pulley reduction), given your average water flow, to supply the torque and RPM to produce the CFM's (and pressure) to properly aerate the pond. This type of calculations makes my head spin and might be a matter of experimentation without consulting a Professional Engineer or someone specialized in water wheels. Sounds like a fun project!

Fish on!,
Noel