In harmony with the general purposes of the Special City Island District and in accordance with the provisions of this Chapter, certain specified regulations of the districts on which the Special City Island District is superimposed are made inapplicable and special regulations are substituted therefor. Except as modified by the express provisions of the Special District, the regulations of the underlying zoning districts remain in force. In flood zones, in the event of a conflict between the provisions of this Chapter and the provisions of Article VI, Chapter 4 (Special Regulations Applying in Flood Zones), the provisions of Article VI, Chapter 4, shall control.