Thanks guys. I appreciate the feedback. I was concerned with the siphoning effect, as I knew it would dramatically increase flow.
I am trying to eyeball the height of the emergency spillways vs the height of the 12" pipe. It's difficult for me, and past experiences are telling me I'm not particularly good at it. (Guessing and comparing elevations) the USDA guy has a laser measuring device. Hopefully he can come by.
Technically, since I built the pond in the woods, and not in an erodible field, he can't offer me much help.
I needed to confirm the spillway process, and you have helped.
Thanks again
This pic shows how much free board I have, at 4" above full pool. 1 AC pond, with 8 AC of drainage. It also shows spillway on right side of dam. There's an identical one on the left side.

Last edited by SetterGuy; 07/27/15 05:37 PM.
9 yr old pond, 1 ac, 15' deep.
RES, YP, GS, FHM (no longer), HBG (going away), SMB, and HSB (only one seen in 5 yrs) Restocked HSB (2020) Have seen one of these.
I think that's about all I should put in my little pond.
Otter attack in 2023