You're right, it's not a siphon, it's a straight outlet pipe. The engineer isn't "signing off" on the repair...just offering his advice.
You mentioned lowering the water level. What are the reasons for this? We have two ponds, one about an acre and the other about 1/2 acre. I'm thinking if I needed to lower the water for vegetation it wouldn't take too long to pump out a couple of feet. Hopefully if we do this renovation right, we're able to catch the sediment at the head of the pond where we can easily clean it later without draining the whole pond. Plus it drains off CRP land and shouldn't silt too bad at this point.
Having said all that, I really want to do this right the first time...not too interested in starting this process over in five years.
