Thank you both for the feedback. We decided to go with an in-line Agri Drain box. We used 6” pipe, and put the top of the intake pipe 30 inches below the pond water level. Hopefully this is more than enough to keep it out of the way of ice. FishinRod I like your solution, it seems very simple and elegant. The only advantage I see to the Agri Drain system is being able to control the water level when the ice starts to melt. We are going to install a solid dock with the underside 9 inches above the water, so having the overflow operable in the spring should allow us to keep the water level consistent during the spring melt so it doesn’t raise the ice and pop the dock off it’s piers. We will see how well that works.

The Agri Drain box we ordered is 5 feet tall, so most of the intake is at least 4.5 feet below ground level, out of the way of frost. We also put two Agri Drain anti seep collars on both sides of the box, and packed it all well. As I told the guy packing it, this is the most dangerous part of the pond, so let’s get it right. He seems to have done a good job, so we will see what happens when we bring the pond to full pool.