Those pipes almost look like a way to monitor the water level visually. Not sure they would be tied to a drain or capable of flowing much volume but it is possible and it would be scary to find that out the hard way lol.

I would look at the pond and the surrounding areas keeping in mind "If you were to drain the water, where would the most logical place for the drained water to go be?" Look at the lay of the land, look for low spots where water would run off, near by streams etc.. Then look in those areas for a larger pipe.

I would walk around the pond and look for any piping that could evacuate the water. Maybe see where the natural over flow is and check in that area for pipes. Usually the drain would be 4" or much larger. Some ponds have the drains a couple feet into the water so don't be afraid to look extra hard and even look a few feet into the water. I have a pond in the family that has a 6" pipe with a 90 elbow on it an sometimes weeds cover it over. Even though I know exactly where it is, it can be difficult to see it.

If the pond has a drain like some do called the "agri-drain" those types of drains have stop logs in them that can be removed to lower the water level or drain the pond.

Let us know what you find