Thank you all for taking the time to think through this with me!! I feel like I have a better idea definitely of how to handle this now, and I feel better about the whole thing. I got some great suggestions I can work with. Incidentally, my neighbor who keeps chickens also told me today that he'd been having similar problems and one of the things that he did was build up a couple terraces. Kind of like speed bumps on the dirt. Tall enough to make a difference in how much water flows downward, but not so tall that he can't take his riding mower right over it.