Lots of variables to consider, Jim K; those with more knowledge than me will no doubt chime in, but let me tell you about my experience with a thru the dam drain.
Pond: 3-4 acre, 17 feet deep, 700 ft wraparound berm, 90 feet thick at drain point. Twelve inch pvc sewer pipe overflow.Filled this winter, no leaks.
High pitched screech from lake end of drain pipe noticed in early February with noncoincident efflux of water in rapidly increasing stream from end of drainpipe. Changed pants. Plugged downstream end of pipe while stream was only at 9/10ths full flow. No joke-it took 3 men, a tractor, and a telephone pole and everyone got hypothermia, even the tractor. Capped sewer pipe, then built a form and put in 50 bags of concrete.
The contractor had not sealed the pipe properly, nor placed it in concrete, and as the dam settled, the joints in the dam gradually separated.
So whichever you choose, make sure your contractor really knows what he's doing. Myself, I'll never have another dam with anything hollow going thru it.
Oh and by the way, welcome to PB, I didn't catch your first post.
