My reservations are many. I think the biggest is location. From what I gather you are right off of Lake Ontario. A lake formed by glaciers and limestone scraping. It looks to me you are in a old Karst area. I think Howe Caverns are not a great distance from you either. And a great deal of indicators are there. The vertical movement of water with springs. The abundance of large limestome formations, including the possible broken up pavement stones everywhere. These could be in multiple depths, in your pond, under your pond, under your dam and embankments.
My biggest concern is complex underground drainage. Aquifers and piping. Bear in mind with the water you are adding you are almost doubling the atmospheric pressures at the pond bottom, dam and embankment foundations. Pressures this soil has probably never seen. You will be, and this is not a maybe, redirecting underground water. Just where is the big question.
I think you could create an inverted funnel sinkhole. Or possibly push into a aquifer. Maybe even create piping under your dam or embankments. With this in mind I may have not stacked all that rock and fabric everywhere. It prevents you from inspecting the pond side of the embankments. Especially at the base.
I don't know if you could have done much to change that. I think I would have done numerous core samples. I would have done a Proctor test and a sieve test. If all of these were satisfactory I would then judge how to treat the foundations and the catchment. Might have to escavate and bring in clay, bentonite, who knows. Maybe mulitple levels. I also would have used a sheeps foot for compaction. You just dont get the psi with anything else. Keep it bare, clean banks and bottom and fill it up and test it out. Drain it and inspect it.
Never saw the completed spillway but I don't think overtopping is an issue at all. My main concerns would be the rock formations and the foundations. Well, at least you may make a lot of new springs. I appreciate your efforts. I personally would have made a great pyramid out of those rocks. Hard to really say what is going to happen as that is rare geology you have there. I hope my concerns are unfounded and everything goes as planned.
