Vamaz,

You are correct in your understanding!

The concrete box in the picture is the drop inlet and it is leaking at the connection of the drop inlet and outlet pipe that exits backside of dam.

I agree on the flow issue but my inflow from runoff is measure by gallons or tens of gallons per minute and the leak (at least for now) is maybe half a gallon per minute.

My fear is not that the water will erode the cement at the poor connection, but that FREEZE will cause whatever water is leaking to expand the gap that it has found already and the tiny leak becomes a giant leak.

Maybe I am paranoid because ice recently caused me to lose half of the pond at last failure.

Do you think ice could expand that leak?

Or... do you think that ice could cause pressure on that plastic pipe in such a way that it compresses or deforms enough to let even more water run around it?

Maybe I can pour a concrete "hood" over the top of and down along the sides of that exposed pipe?