This is absolutely correct.It's in a 100 year flood plain. You can't alter the elevation by bringing in or removing earth. You can move it from one side of the property to the other.
you can not remove it from the property.
Parts of our gun range is built into the flood plain. We just had enough room to build a 300 yard range without permits.
Our original intention was to build a 400 yard range but the permits from the feds as well as the costs to have inspectors brought in to survey and determine if we would alter the natural flow of water was prohibitive.