In reality, I don't think head pressure would even play a role, the water is already there thanks to gravity. The only factor that would have a highly measurable effect would be the drop of the outlet because that water is not there at least until the siphon starts. Theres only one way to effect the flow in his circumstance and that's raise the inlet, or lower the outlet.
The ultimate in his scenario would be to lower behind the pond if he has the grade to do this, my guess is this might not be an option unless he travels a long way from the dam and even then maybe his grade just won't allow for the "easy fix"?
Im curious though Gus......did you guys throw a laser level or Transit and see just how equal the inlet and outlet are? A dozer can move 3' of dirt in minutes.
This whole thing about the weight of the water in the pond actually pushing the water out of the pipe because of its pressure doesn't even register unless the pipe goes straight through the dam and even then.........the pressure is virtually nothing, I think I remember something like .433 or .344
per foot of water regardless if its a watering hole or an ocean, it's nothing unless he's like 50' deep and maybe he is, but even if he is, his horizontal pipe is at the waterline with 0 P.S.I until the siphon starts
