Poseidon,
Rockytopper offers you excellent advice above. I don't know your location, but just today, for example, we received several hours of 2 inch per hour rain...totalling 11.5 inches.
There is no pipe system, none, that could handle the amount of water that flowed through my bottomland areas today. If I had a pond there where hundreds of acres of watershed exists, and only with pipes, it would be gone today. Nothing would be left but a memory.
If at all possible, install natural spillways to handle the excess water that the pipes can't handle when/if you have one of these rain events. Two natural spillways are better than one, but one is certainly better than none, IMO. Good luck with your pond.
