Flood-prone Areas with Nonconforming Buildings or Structures. Structures existing in any identified Flood-prone Areas prior to the enactment of Flood Plain provisions (September 9, 2014), but which are not in compliance with these provisions, may continue to remain provided any modification, Alteration, structural Alteration, reconstruction, or improvement of any kind to an existing Structure, to an extent or amount of less than 50% of its market value, shall be elevated and/or Flood-proofed to the greatest extent possible.