That is exactly what I was looking for. Thank you very much. Any recommendation on pipe size for the 1 acre pond?
It is not just the size of the pond that controls the sizing of the pond overflow pipe. The amount of watershed draining into your pond is probably the most important factor.
What size is your damaged metal pipe? If the dam hasn't washed out since the 1950s, then that size is probably sufficient.
(The siphon will actually flow more water than a gravity drain pipe of the same pipe size. Therefore, if you match your existing pipe size, then you should be good with a properly constructed siphon system.)
