Well that is exactly what I planned to do, but several have said it would not be a good idea to have that much water pressure running in the pipe that goes through the dam. If somehow some of that pipe started leaking due to the pressure it could weaken the core of dam over time.
If you cap it on the inside of the pond (under water) there will not be any water pressure inside the pipe. There will be pressure trying to get inside the pipe, but none within.
