I haved kind of same situation and instead of a pipe I built a concrete overflow that is 4 ft wide and about 6 inches deep with a 2 inch berm in the middle. I have a piece of welded fence wire covered with mesh that sits in the area infront of the raised berm and keep the fish from heading down the drain. If you want a couple of pictures let me know. My pond is about 1/3 acre.