RAH: Thanks for the clarification. At first the pond was tiny. I was basically trying to calculate the water flow from the spring. During a rain the spring picked up extra flow from road runoff and the 3" wasn't adequate.
I made the pond bigger (it is around 3-4K sq. ft.) because the water flow was good. I plan on going with a 6 inch pipe.
When you talk about high spots in the drain pipe, are you referring to the horizontal portion in the dike?
