I have a smaller 1.25 acre pond with 25+ acre watershed. I have a ditch that runs from above the pond down past the dam and a concrete weir/board gate to control how much water goes into the pond through a 12" conduit (oversized for me). Most of the water stays in the ditch but your could reverse this and have most of the water go into the culvert. It looks like the left side of the pond is steep and quite wooded. If the right side is less steep or less wooded, I would think that a conduit or pipe (as FishinRod describes) combined with a poured concrete structure could work. Some pictures might be found in this previous post.
GateAnother thought, similar to the upstream settling pond would be to employ a series of settling check dams. The idea is that the check dams are spaced so that, when filled, each dam backs up water to just below the previous dam. This is shown by NY state in the figure. I have used these structures to control the flow in my main drainage ditch.
