"Did your previous 5-acre lake receive all of the flow of the incoming creek? With no outlet pipe? Are you saying that under "normal" conditions there was a continuous amount of roughly 750 GPM flowing over the earthen emergency spillway? Or was the gate used for "draining" the water inflows, as opposed to draining down the lake?"

Yes, no outlet pipe for flow, only for draining the entire contents. Keep in mind that I was minus 2 years old when they decided to 'controlled bust' the concrete dam that had stood for about 23 years, so what is truth vs. folklore is in play, lol. One dam side remains locked into the red clay bank, whereas the opposing end was placed against sedimentary rock. My Dad (now 71) says that he remembers that the dam was not a true 3:1, and had small leaks throughout. Built around 1949, he also doesn't believe a solid core trench was dug.

My initial thoughts were to bust up the remaining concrete, and place that in the emergency spillway. But yes, the entire dam will be made from red clay, core trenched, packed in lifts, etc.

My local culvert supplier does not like/sell galvanized piping, and the max height of his PVC riser is 14ft. Our lake was closer to 20' at the dam when built.