I am curious as to how you found out that the ODNR has to approve all modifications to the pond? What makes this pond different, etc? I would contact Bill Cody and see if he knows anyone out your way that deals with pond repairs. If there is, they may know how to work with these entities to get your work done. Bill's in Ohio, west of you.
Hard to believe that a siphon system wouldn't be allowed, if installed properly. I would think that it could handle more water than a same size regular pipe.
