For starters, I'm just going to say that we have a couple of experienced posters on this board in this thread.
I think that a lot of the legal stuff has been adequately addressed, so I'm only going to bring up some other issues. I'm not intending to intrude on any of that.
For starters, the OP has not gone to elected representatives as far as we know. Any "district" under the drainage laws are also subject, somewhere, to elected representatives. I'm not getting any sense that the appeal to the elected representatives has been tried.
I am also puzzled by the fact that the OP disputed the right of the "District" and it did not immediately retreat to higher management for further advice. The point is that in my experience, once a dispute is initiated, most organizations require as a matter of policy, to pull off of a job and let someone beyond the pickup truck to do the next negotiations.

