Would have liked to put in a lot bigger pipe. Could have and probably should have put in multiple small pipes.
But the problem with the large pipe was, I still had to put an emergency overflow about 8" above the bottom (full pool) of the overflow pipe. So the largest pipe of any value would have been an 8" (which is what I should have used in retrospect)(edit: that is an 8" pipe. I don't know what I was thinking when I posted itm as a 6"). The reason is, if I did not allow for large flow at that level, we would back water back out into the ag field, pond it up, and break over the top of the terrace. The overflow has to carry the flow of the terrace, slowed down by a double culvert that passes under a farm road at the top of the hill. Even at the levels I've set the pipe and emergency we still back some water temporarily in the field. But we have it about right so it only stands for about an hour at most and maybe half an acre. Acceptable to me to gain the benefits of maximum available water capacity and full pool height of the sediment pond. Just one of the compromises I had to make with the pond being nearly at the top of the hill.
Concrete on each end, and a couple of concrete anti-seep collars in the middle.
No one in their right mind would hire me to do concrete work. Yet I see stuff my dad mixed up 50 years ago by hand still pretty solid made of portland cement and chat (chirt from lead/zink mine tailings - not the best aggregate because of acid content). I actually used some of his old slabs that came from around the old barn at the exit of the emergency overflow to keep it from eroding the bank as the water fell into the pond. This concrete is mixed with a 3pt tractor mixer. It will be around longer than I will.
I usually sucker my oldest grandson Bret to do the shoveling stuff into the mixer. He is a pretty stout lad. He helped with all of this.
