Can my downhill neighbor put up a berm to obstruct the natural drainage of water from my lawn across his lawn?

That's what he's done. I have pictures that show my lawn naturally draining into the lot that his house is on before the house was even built. But since his father is an excavation contractor, he's since imported 5 truckloads of dirt to raise the grade on his lawn up--by as much as 2 feet at places. I now have a drainage problem in the water that would have naturally flowed down through his lawn.

Not wanting to make an enemy, I first tried to address the problem by putting in a catch basin at the lowest point in my lawn and running a corrugated pipe out to the neighborhood water feature. Got a nasty letter from the HOA telling me to remove the pipe from the outlot, so now I'm left with no options.

I approached neighbor with the problem (and the HOA letter) for the 3rd time and he said no way is he regrading his lawn to let my water drain out through his yard (it's not even sodded yet). Instead, he told me I should rip up my landscaping, take down my fence, and regrade my own lawn to fill it up higher so my water can drain another way.

If he created the drainage problem, shouldn't he be the one to fix it? Aren't there laws that compel him to fix it? I need to balance standing up for myself with making an enemy. But I can't imagine that this guy didn't realize what he was doing when he imported all that dirt. Yet he did it anyway--so why am I the only one worried about turning a potential neighbor into an adversary?

Any thoughts? Are there laws that govern this stuff?

Thanks,

gardenerzone4