Usually, "they" won't permit a private levee in a flood plain if it alters the flow of flood waters to make them higher at any point off the property the levee is on.
+1 My pond is in a 100 year flood plain. In Illinois, at least when I dug my pond in 2013, it was ok to build a pond in a flood plain but I could not raise the grade more than 1 foot, so no berm/levee allowed.