Culvert options?

[JJT]

I'd avoid the flexible pipe, it doesn't take much of a load and it's a pain to lay perfectly flat, any humps and you've built yourself a trap for silt to collect. Heck sewer and drain pipe can take a decent load and it's only 4-5 bucks for a 10'section. Spec out the drain area, you may need to upsize the drain pile. A 4" pipe wont take more than a couple of of gutter downspots.

I have a pair of 6" pipes leading into my pond, they start at the edge of my driveway and drain maybe an acre. At least 2 - 3 times a year we'll get a heavy rain storm and these drains will get over run for a few hours.