Pond Boss Forums POND CONSTRUCTION Building a dam Overflow pipe size

OK just reread your 1st post you are sizing the main spillway not the emergency drain. But I would still not change size of the vertical pipe other than the bell on top. You will need to make it so when the beavers come back ( and they will ), they can not block drain very easily.
Brother has a 2 acre pond that 40 acres drains into and has a 12 inch pipe and has worked great for the past 10 years. We even went threw a 13 inch rain once.