It looks like you could possibly have a large amount of water come through your pond during a heavy rain. you should probably plan a worst case scenario. the creek that feeds my pond is dry eight months out of the year but in the spring it can become a river. My pond has been completed for four years now and we have had two fifty year floods since then. I have a twenty inch drain pipe going through the dam as an overflow and two emergency spillways.
Here is a picture of the road near the spillway after water had come over the spillway and removed the gravel from the road and put it below the dam. After this happened I had one of the emergency spillways widened about twenty feet because the water came within a couple of feet from going over the dam.
