The water drains out of the pond back behind the pond grade. The draw behind the pond certainly runs while the pond is going down and it appears like the water starts close to the base of the back side of the dam. It's difficult to tell since it's more of just a marshy area than a simple stream.
A few pictures:
Upper circled area is a previously patched hole. I dug out a rectangular area, plugged with bentonite powder, covered with thick pond liner and then held down with large rocks. The lower circled area marks the new 4" diameter hole.
4" diameter drain hole.
Culvert (left arrow) marks the pond 'high point.' You can see how far down the water level is. You can also see how far away the current hole is from the grade.
