I'm new to this forum, so please bear with me until I learn the ropes.

I have a 3 acre pond, about 25 feet deep in the middle. It's about 30 years old.
It's built into South Carolina red clay. No leaks from the dam. However, with the rains we got a couple days ago, my spillway was basically destroyed. The spillway was about 40 feet long and five feet wide built out of concrete (without rebar or any steel). It had about 11 feet of fall in 40 feet.
In about 20 minutes enough rain and runoff hit the spillway and looks like the water got under the concrete and moved all the slabs to the bottom of the spillway and left them in a giant pile. The only concrete remaining was at the top of the spillway and it has about five feet of dirt holding back the pond. I'm thinking that concrete didn't go with the rest because there was riprap at the top of the spillway and perhaps it slowed the water down just enough to prevent erosion. However, now there is seepage from the remaining spillway holding back the dirt. I'm not sure how to fix that. The contractor wants to dig a bucket wide trench across the spillway, 4 feet deep, put rebar in it and fill it with concrete. Any thoughts on this would be very appreciated,

Also, he figures it's going to take about 200 tons of clay to bring the spillway back to original grade and three loads of riprap on top of filter fabric.
Any thoughts on this would also be appreciated.

Last thing. There's an 8 inch steel pipe in the pond that has been capped off about ten years ago because the vertical riser in the water was badly corroded and leaking. I put a plastic cap on it and it's been holding since. My questions are two; If I remove the cap, will I be able to put it back on if water is running out of it like I think it's going to do. Or, is there some way to put a valve on there that might allow me to slide the valve on it in the open position and then close it when the water level is where I need it. The pipe is steel I believe and it's in bad shape. I don't think I can thread it. Is there a valve that would slip on with clamps or something?

I apologize for the really long post. Please help. All the knowledgeable people here are all slammed with work and getting a premium for their work. I need to know the right way to fix this pond so I can attempt to make repairs affordable.

Thank you guys.