Thanks for the info. Looks like I have some homework to do.

The property is adjacent to the calcasieu river, and in the winter and spring the river backs up into it. I tried to build a sandbag berm in the drain, but the sandbags were actually pushed back into the pond when we had a major rain event. So it appears that rather than a drain, it is more like a fill valve.

As far as the length measurements, I didn't have anything to measure them, but would estimate them all to be near 12 inches.

Thanks for the good info guys. I will do the research on what you guys have provided and let you know what I come up with.