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.

Welcome to the forum! You'll find all kinds of good, professional help here for your pond.
If at all possible, please post some pics of the pond and its issues. I believe you will get some ideas from the experts.

valkmancarl, welcome to the forum!

You guys really got hammered by the rain!

I wouldn't touch the old drain pipe. My thoughts are there is too great of a chance if it failing, and it would take the whole dam with it if it did. I would

I would do some research into a siphon drain. That can be put into the pond without disturbing the dam too much, if any, and an 8" siphon drain (or even a 6") will move a LOT more water than the old 8" standpipe type drain.

I don't know for sure how to fix the spillway, but I don't know if 200 tons of clay will be enough. The problem with the riprap is that if you get another heavy rain event, the riprap will most likely end up all piled up at the bottom, like the concrete.

But, definitely get it worked on asap. If the leak gets larger it could blow out the whole dam there at the spillway and the whole pond could be gone.

I'm assuming the emergency spillway routes the water away from the toe of the dam?

If you could swing it, I'd get the clay packed back in there, have the contractor put the cement in like he's planning (with rebar of course) but also tie that into a concrete spillway instead of the riprap - all tied in with rebar. Also put in the plastic pipe siphon drain - that will keep a lot of water from going over the emergency spillway.

I'd go talk to your counties NRCS office. They should be able to tell you how much watershed feeds your pond, and what size the primary overflow pipe should be.

Thanks immensely for your reply. I put in a 6" siphon drain today and have already dropped the water level where spillway is not an issue right now. I'm going to tell my contractor what you suggested for the spillway.
I also thought about taking some quikrete and dry pouring it over the riprap he puts down. Maybe if I drive some rebar at random into the ground and tie the riprap with the concrete maybe it'll have a better chance of surviving another bad rain event.
Thanks again for your time. I really appreciate it.

Glad to hear that the siphon did the trick. I don't know if the regular quickcrete will work, you might need to get the kind that is used for setting posts. It's designed so it could be poured dry into the hole and then water poured on top of it.

I'd be concerned about how tightly it bonds to the riprap.