A pipe AND an emergency spillway is a good way to go as it balances money spent, effort and results. There are bagillions of ponds out there that have a "low spot" in the dam as an overflow that do just fine. I would be willing to bet that the watersheds for those ponds are light for the pond's sizes. Adding a pipe to this scenario with larger more appropriate watersheds allows the owner to pick the size of pipe that allows pond drainage under normal rainfall/snow melt events while using the freeboard (distance from pipe to top of emergency spillway) as a catch basin so that the E. Spillway rarely gets used. The excessive water overtakes the drain pipe, but the pond will still hold more water until it starts to flow over the dam at the E. spillway. This reduces the E. spillways usage which reduces the erosion and allows grasses and such on the E spillway to recover before excessive waters are experienced again.

My 1/4 acre pond has an excessive watershed, a 15 inch doublewall corrugated drain pipe, 2 to 3 foot of freeboard and may use the E.spillway once every few years (cross my fingers). The pond was initially installed as a catch basin to reduce the flooding of the home and cattle yard. It does it's job and has been affordable.

The siphon type drains have many advantages...takes water from the bottom of the pond which is usually low in oxygen and high in sediments. If set up right, they can also be used as a drain to empty the pond. But, they may cost you more money, especially when installing in a filled pond. You'll have to check into the siphon costs for your pond's specifications to determine if its affordable for you. You can imagine the cost difference between a 15 siphon drain (what I would need) compared to a 6" PVC siphon drain for a pond with less watershed.

Fish on!,
Noel